31.5.2008   

EN

Official Journal of the European Union

L 142/1


COUNCIL REGULATION (EC) No 440/2008

of 30 May 2008

laying down test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH)

(Text with EEA relevance)

THE COMMISSION OF THE EUROPEAN COMMUNITIES,

Having regard to the Treaty establishing the European Community,

Having regard to Regulation (EC) No 1907/2006 of 18 December 2006 of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), establishing a European Chemicals Agency, amending Directive 1999/45/EC and repealing Council Regulation (EEC) No 793/93 and Commission Regulation (EC) No 1488/94 as well as Council Directive 76/769/EEC and Commission Directives 91/155/EEC, 93/67/EEC, 93/105/EC and 2000/21/EC (1), and in particular Article 13(3)thereof,

Whereas:

(1)

Pursuant to Regulation (EC) No 1907/2006, test methods are to be adopted at Community level for the purposes of tests on substances where such tests are required to generate information on intrinsic properties of substances.

(2)

Council Directive 67/548/EEC of 27 June 1967 on the approximation of the laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances (2), laid down, in Annex V, methods for the determination of the physico-chemical properties, toxicity and ecotoxicity of substances and preparations. Annex V to Directive 67/548/EEC has been deleted by Directive 2006/121/EC of the European Parliament and of the Council with effect from 1 June 2008.

(3)

The test methods contained in Annex V to Directive 67/548/EEC should be incorporated into this Regulation.

(4)

This Regulation does not exclude the use of other test methods, provided that their use is in accordance with Article 13(3) of Regulation 1907/2006.

(5)

The principles of replacement, reduction and refinement of the use of animals in procedures should be fully taken into account in the design of the test methods, in particular when appropriate validated methods become available to replace, reduce or refine animal testing.

(6)

The provisions of this Regulation are in accordance with the opinion of the Committee established under Article 133 of Regulation (EC) No 1907/2006,

HAS ADOPTED THIS REGULATION:

Article 1

The test methods to be applied for the purposes of Regulation 1907/2006/EC are set out in the Annex to this Regulation.

Article 2

The Commission shall review, where appropriate, the test methods contained in this Regulation with a view to replacing, reducing or refining testing on vertebrate animals.

Article 3

All references to Annex V to Directive 67/548/EEC shall be construed as references to this Regulation.

Article 4

This Regulation shall enter into force on the day following its publication in the Official Journal of the European Union.

It shall apply from 1 June 2008.

Done at Brussels, 30 May 2008.

For the Commission

Stavros DIMAS

Member of the Commission


(1)   OJ L 396, 30.12.2006, p. 1, as corrected by OJ L 136, 29.5.2007, p. 3.

(2)   OJ  196, 16.8.1967, p. 1. Directive as last amended by Directive 2006/121/CE of the European Parliament and of the Council (OJ L 396, 30.12.2006, p. 850, as corrected by OJ L 136, 29.5.2007, p. 281).


ANNEX

PART A: METHODS FOR THE DETERMINATION OF PHYSICO-CHEMICAL PROPERTIES

TABLE OF CONTENTS

A.1.

MELTING/FREEZING TEMPERATURE 4

A.2.

BOILING TEMPERATURE 14

A.3.

RELATIVE DENSITY 21

A.4.

VAPOUR PRESSURE 26

A.5.

SURFACE TENSION 50

A.6.

WATER SOLUBILITY 57

A.8.

PARTITION COEFFICIENT 67

A.9.

FLASH-POINT 80

A.10.

FLAMMABILITY (SOLIDS) 82

A.11.

FLAMMABILITY (GASES) 85

A.12.

FLAMMABILITY (CONTACT WITH WATER) 87

A.13.

PYROPHORIC PROPERTIES OF SOLIDS AND LIQUIDS 91

A.14.

EXPLOSIVE PROPERTIES 93

A.15.

AUTO-IGNITION TEMPERATURE (LIQUIDS AND GASES) 104

A.16.

RELATIVE SELF-IGNITION TEMPERATURE FOR SOLIDS 106

A.17.

OXIDISING PROPERTIES (SOLIDS) 109

A.18.

NUMBER — AVERAGE MOLECULAR WEIGHT AND MOLECULAR WEIGHT DISTRIBUTION OF POLYMERS 114

A.19.

LOW MOLECULAR WEIGHT CONTENT OF POLYMERS 123

A.20.

SOLUTION/EXTRACTION BEHAVIOUR OF POLYMERS IN WATER 131

A.21.

OXIDISING PROPERTIES (LIQUIDS) 135

A.1.   MELTING/FREEZING TEMPERATURE

1.   METHOD

The majority of the methods described are based on the OECD Test Guideline (1). The fundamental principles are given in references (2) and (3).

1.1.   INTRODUCTION

The methods and devices described are to be applied for the determination of the melting temperature of substances, without any restriction with respect to their degree of purity.

The selection of the method is dependent on the nature of the substance to be tested. In consequence the limiting factor will be according to, whether or not the substance can be pulverised easily, with difficulty, or not at all.

For some substances, the determination of the freezing or solidification temperature is more appropriate and the standards for these determinations have also been included in this method.

Where, due to the particular properties of the substance, none of the above parameters can be conveniently measured, a pour point may be appropriate.

1.2.   DEFINITIONS AND UNITS

The melting temperature is defined as the temperature at which the phase transition from solid to liquid state occurs at atmospheric pressure and this temperature ideally corresponds to the freezing temperature.

As the phase transition of many substances takes place over a temperature range, it is often described as the melting range.

Conversion of units (K to oC)

t = T - 273,15

t

:

Celsius temperature, degree Celsius (oC)

T

:

thermodynamic temperature, kelvin (K)

1.3.   REFERENCE SUBSTANCES

Reference substances do not need to be employed in all cases when investigating a new substance. They should primarily serve to check the performance of the method from time to time and to allow comparison with results from other methods.

Some calibration substances are listed in the references (4).

1.4.   PRINCIPLE OF THE TEST METHOD

The temperature (temperature range) of the phase transition from the solid to the liquid state or from the liquid to the solid state is determined. In practice while heating/cooling a sample of the test substance at atmospheric pressure the temperatures of the initial melting/freezing and the final stage of melting/freezing are determined. Five types of methods are described, namely capillary method, hot stage methods, freezing temperature determinations, methods of thermal analysis, and determination of the pour point (as developed for petroleum oils).

In certain cases, it may be convenient to measure the freezing temperature in place of the melting temperature.

1.4.1.   Capillary method

1.4.1.1.   Melting temperature devices with liquid bath

A small amount of the finely ground substance is placed in a capillary tube and packed tightly. The tube is heated, together with a thermometer, and the temperature rise is adjusted to less than about 1 K/min during the actual melting. The initial and final melting temperatures are determined.

1.4.1.2.   Melting temperature devices with metal block

As described under 1.4.1.1, except that the capillary tube and the thermometer are situated in a heated metal block, and can be observed through holes in the block.

1.4.1.3.   Photocell detection

The sample in the capillary tube is heated automatically in a metal cylinder. A beam of light is directed through the substance, by way of a hole in the cylinder, to a precisely calibrated photocell. The optical properties of most substances change from opaque to transparent when they are melting. The intensity of light reaching the photocell increases and sends a stop signal to the digital indicator reading out the temperature of a platinum resistance thermometer located in the heating chamber. This method is not suitable for some highly coloured substances.

1.4.2.   Hot stages

1.4.2.1.   Kofler hot bar

The Kofler hot bar uses two pieces of metal of different thermal conductivity, heated electrically, with the bar designed so that the temperature gradient is almost linear along its length. The temperature of the hot bar can range from 283 to 573 K with a special temperature-reading device including a runner with a pointer and tab designed for the specific bar. In order to determine a melting temperature, the substance is laid, in a thin layer, directly on the surface of the hot bar. In a few seconds a sharp dividing line between the fluid and solid phase develops. The temperature at the dividing line is read by adjusting the pointer to rest at the line.

1.4.2.2.   Melt microscope

Several microscope hot stages are in use for the determination of melting temperatures with very small quantities of material. In most of the hot stages the temperature is measured with a sensitive thermocouple but sometimes mercury thermometers are used. A typical microscope hot stage melting temperature apparatus has a heating chamber which contains a metal plate upon which the sample is placed on a slide. The centre of the metal plate contains a hole permitting the entrance of light from the illuminating mirror of the microscope. When in use, the chamber is closed by a glass plate to exclude air from the sample area.

The heating of the sample is regulated by a rheostat. For very precise measurements on optically anisotropic substances, polarised light may be used.

1.4.2.3.   Meniscus method

This method is specifically used for polyamides.

The temperature at which the displacement of a meniscus of silicone oil, enclosed between a hot stage and a cover-glass supported by the polyamide test specimen, is determined visually.

1.4.3.   Method to determine the freezing temperature

The sample is placed in a special test tube and placed in an apparatus for the determination of the freezing temperature. The sample is stirred gently and continuously during cooling and the temperature is measured at suitable intervals. As soon as the temperature remains constant for a few readings this temperature (corrected for thermometer error) is recorded as the freezing temperature.

Supercooling must be avoided by maintaining equilibrium between the solid and the liquid phases.

1.4.4.   Thermal analysis

1.4.4.1   Differential thermal analysis (DTA)

This technique records the difference in temperatures between the substance and a reference material as a function of temperature, while the substance and reference material are subjected to the same controlled temperature programme. When the sample undergoes a transition involving a change of enthalpy, that change is indicated by an endothermic (melting) or exothermic (freezing) departure from the base line of the temperature record.

1.4.4.2   Differential scanning calorimetry (DSC)

This technique records the difference in energy inputs into a substance and a reference material, as a function of temperature, while the substance and reference material are subjected to the same controlled temperature programme. This energy is the energy necessary to establish zero temperature difference between the substance and the reference material. When the sample undergoes a transition involving a change of enthalpy, that change is indicated by an endothermic (melting) or exothermic (freezing) departure from the base line of the heat flow record.

1.4.5.   Pour point

This method was developed for use with petroleum oils and is suitable for use with oily substances with low melting temperatures.

After preliminary heating, the sample is cooled at a specific rate and examined at intervals of 3 K for flow characteristics. The lowest temperature at which movement of the substance is observed is recorded as the pour point.

1.5.   QUALITY CRITERIA

The applicability and accuracy of the different methods used for the determination of the melting temperature/melting range are listed in the following table:

TABLE: APPLICABILITY OF THE METHODS

A.   Capillary methods

Method of measurement

Substances which can be pulverised

Substances which are not readily pulverised

Temperature range

Estimated accuracy (1)

Existing standards

Melting temperature devices with liquid bath

yes

only to a few

273 to 573 K

±0,3  K

JIS K 0064

Melting temperature with metal block

yes

only to a few

293 to >573 K

±0,5  K

ISO 1218 (E)

Photocell detection

yes

several with appliance devices

253 to 573 K

±0,5  K

 


B.   Hot stages and freezing methods

Method of measurement

Substances which can be pulverised

Substances which are not readily pulverised

Temperature range

Estimated accuracy (2)

Existing standards

Kofler hot bar

yes

no

283 to > 573 K

± 1K

ANSI/ASTM D 3451-76

Melt microscope

yes

only to a few

273 to > 573 K

±0,5  K

DIN 53736

Meniscus method

no

specifically for polyamides

293 to > 573 K

±0,5  K

ISO 1218 (E)

Freezing temperature

yes

yes

223 to 573 K

±0,5  K

e.g. BS 4695


C.   Thermal analysis

Method of measurement

Substances which can be pulverised

Substances which are not readily pulverised

Temperature range

Estimated accuracy (3)

Existing standards

Differential thermal analysis

yes

yes

173 to 1 273  K

up to 600 K ±0,5 K up to 1 273 K ±2,0 K

ASTM E 537-76

Differential scanning calorimetry

yes

yes

173 to 1 273  K

up to 600 K ±0,5 K up to 1 273 K ±2,0 K

ASTM E 537-76


D.   Pour point

Method of measurement

Substances which can be pulverised

Substances which are not readily pulverised

Temperature range

Estimated accuracy (4)

Existing standards

Pour point

for petroleum oils and oily substances

for petroleum oils and oily substances

223 to 323 K

±0,3  K

ASTM D 97-66

1.6.   DESCRIPTION OF THE METHODS

The procedures of nearly all the test methods have been described in international and national standards (see Appendix 1).

1.6.1.   Methods with capillary tube

When subjected to a slow temperature rise, finely pulverised substances usually show the stages of melting shown in figure 1.

Figure 1

Image 1

Stage A

Stage B

Stage C

Stage D

Stage E

Stage A

(beginning of melting): fine droplets adhere uniformly to the inside wall of the capillary tube

Stage B

a clearance appears between the sample and the inside wall due to shrinkage of the melt

Stage C

the shrunken sample begins to collapse downwards and liquefies

Stage D

a complete meniscus is formed at the surface but an appreciate amount of the sample remains solid

Stage E

(final stage melting): there are no solid particles

During the determination of the melting temperature, the temperatures are recorded at the beginning of the melting and at the final stage.

1.6.1.1.   Melting temperature devices with liquid bath apparatus

Figure 2 shows a type of standardised melting temperature apparatus made of glass (JIS K 0064); all specifications are in millimeters.

Figure 2

Image 2

A: Measurement vessel

B: Stopper

C: Vent

D: Thermometer

E: Auxiliary thermometer

F: Bath liquid

G: Capillary tube made of glass, 80 to 100 mm in length, 1,0 ± 0,2 mm inner diameter, 0,2 to 0,3 mm wall thickness

H: Side tube

Bath liquid:

A suitable liquid should be chosen. The choice of the liquid depends upon the melting temperature to be determined, e.g. liquid paraffin for melting temperatures no higher than 473 K, silicone oil for melting temperatures no higher than 573 K.

For melting temperatures above 523 K, a mixture consisting of three parts sulphuric acid and two parts potassium sulphate (in mass ratio) can be used. Suitable precautions should be taken if a mixture such as this is used.

Thermometer:

Only those thermometers should be used which fulfil the requirements of the following or equivalent standards:

ASTM E 1-71, DIN 12770, JIS K 8001.

Procedure:

The dry substance is finely pulverised in a mortar and is put into the capillary tube, fused at one end, so that the filling level is approximately 3 mm after being tightly packed. To obtain a uniform packed sample, the capillary tube should be dropped from a height of approximately 700 mm through a glass tube vertically onto a watch glass.

The filled capillary tube is placed in the bath so that the middle part of the mercury bulb of the thermometer touches the capillary tube at the part where the sample is located. Usually the capillary tube is introduced into the apparatus about 10 K below the melting temperature.

The bath liquid is heated so that the temperature rise is approximately 3 K/min. The liquid should be stirred. At about 10 K below the expected melting temperature the rate of temperature rise is adjusted to a maximum of 1 K/min.

Calculation:

The calculation of the melting temperature is as follows:

T = TD + 0,00016 (TD - TE) n

where:

T

=

corrected melting temperature in K

TD

=

temperature reading of thermometer D in K

TE

=

temperature reading of thermometer E in K

n

=

number of graduations of mercury thread on thermometer D at emergent stem.

1.6.1.2.   Melting temperature devices with metal block

Apparatus:

This consists of:

a cylindrical metal block, the upper part of which is hollow and forms a chamber (see figure 3),

a metal plug, with two or more holes, allowing tubes to be mounted into the metal block,

a heating system, for the metal block, provided for example by an electrical resistance enclosed in the block,

a rheostat for regulation of power input, if electric heating is used,

four windows of heat-resistant glass on the lateral walls of the chamber, diametrically disposed at right-angles to each other. In front of one of these windows is mounted an eye-piece for observing the capillary tube. The other three windows are used for illuminating the inside of the enclosure by means of lamps,

a capillary tube of heat-resistant glass closed at one end (see 1.6.1.1).

Thermometer:

See standards mentioned in 1.6.1.1. Thermoelectrical measuring devices with comparable accuracy are also applicable.

Figure 3

Image 3

Thermometer

Capillary tube

Metal plug

Eye-piece

Lamp

Electrical resistance

Metal heating block

1.6.1.3.   Photocell detection

Apparatus and procedure:

The apparatus consists of a metal chamber with automated heating system. Three capillary are filled accordingly to 1.6.1.1 and placed in the oven.

Several linear increases of temperature are available for calibrating the apparatus and the suitable temperature rise is electrically adjusted at a pre-selected constant and linear rate. recorders show the actual oven temperature and the temperature of the substance in the capillary tubes.

1.6.2.   Hot stages

1.6.2.1.   Kofler hot bar

See Appendix.

1.6.2.2.   Melt microscope

See Appendix.

1.6.2.3.   Meniscus method (polyamides)

See Appendix.

The heating rate through the melting temperature should be less than 1 K/min.

1.6.3.   Methods for the determination of the freezing temperature

See Appendix.

1.6.4.   Thermal analysis

1.6.4.1.   Differential thermal analysis

See Appendix.

1.6.4.2.   Differential scanning calorimetry

See Appendix.

1.6.5.   Determination of the pour point

See Appendix.

2.   DATA

A thermometer correction is necessary in some cases.

3.   REPORTING

The test report shall, if possible, include the following information:

method used,

precise specification of the substance (identity and impurities) and preliminary purification step, if any,

an estimate of the accuracy.

The mean of at least two measurements which are in the range of the estimated accuracy (see tables) is reported as the melting temperature.

If the difference between the temperature at the beginning and at the final stage of melting is within the limits of the accuracy of the method, the temperature at the final stage of melting is taken as the melting temperature; otherwise the two temperatures are reported.

If the substance decomposes or sublimes before the melting temperature is reached, the temperature at which the effect is observed shall be reported.

All information and remarks relevant for the interpretation of results have to be reported, especially with regard to impurities and physical state of the substance.

4.   REFERENCES

(1)

OECD, Paris, 1981, Test Guideline 102, Decision of the Council C(81) 30 final.

(2)

IUPAC, B. Le Neindre, B. Vodar, eds. Experimental thermodynamics, Butterworths, London 1975, vol. II, p. 803-834.

(3)

R. Weissberger ed.: Technique of organic Chemistry, Physical Methods of Organic Chemistry, 3rd ed., Interscience Publ., New York, 1959, vol. I, Part I, Chapter VII.

(4)

IUPAC, Physicochemical measurements: Catalogue of reference materials from national laboratories, Pure and applied chemistry, 1976, vol. 48, p. 505-515.

Appendix

For additional technical details, the following standards may be consulted for example.

1.   Capillary methods

1.1.   Melting temperature devices with liquid bath

ASTM E 324-69

Standard test method for relative initial and final melting points and the melting range of organic chemicals

BS 4634

Method for the determination of melting point and/or melting range

DIN 53181

Bestimmung des Schmelzintervalles von Harzen nach Kapillarverfarehn

JIS K 00-64

Testing methods for melting point of chemical products

1.2.   Melting temperature devices with metal block

DIN 53736

Visuelle Bestimmung der Schmelztemperatur von teilkristallinen Kunststoffen

ISO 1218 (E)

Plastics — polyamides — determination of ‘melting point’

2.   Hot stages

2.1.   Kofler hot bar

ANSI/ASTM D 3451-76

Standard recommended practices for testing polymeric powder coatings

2.2.   Melt microscope

DIN 53736

Visuelle Bestimmung der Schmelztemperatur von teilkristallinen Kunststoffen

2.3.   Meniscus method (polyamides)

ISO 1218 (E)

Plastics — polyamides — determination of ‘melting point’

ANSI/ASTM D 2133-66

Standard specification for acetal resin injection moulding and extrusion materials

NF T 51-050

Résines de polyamides. Détermination du ‘point de fusion’ méthode du ménisque

3.   Methods for the determination of the freezing temperature

BS 4633

Method for the determination of crystallising point

BS 4695

Method for Determination of Melting Point of petroleum wax (Cooling Curve)

DIN 51421

Bestimmung des Gefrierpunktes von Flugkraftstoffen, Ottokraftstoffen und Motorenbenzolen

ISO 2207

Cires de pétrole: détermination de la température de figeage

DIN 53175

Bestimmung des Erstarrungspunktes von Fettsäuren

NF T 60-114

Point de fusion des paraffines

NF T 20-051

Méthode de détermination du point de cristallisation (point de congélation)

ISO 1392

Method for the determination of the freezing point

4.   Thermal analysis

4.1.   Differential thermal analysis

ASTM E 537-76

Standard method for assessing the thermal stability of chemicals by methods of differential thermal analysis

ASTM E 473-85

Standard definitions of terms relating to thermal analysis

ASTM E 472-86

Standard practice for reporting thermoanalytical data

DIN 51005

Thermische Analyse, Begriffe

4.2.   Differential scanning calorimetry

ASTM E 537-76

Standard method for assessing the thermal stability of chemicals by methods of differential thermal analysis

ASTM E 473-85

Standard definitions of terms relating to thermal analysis

ASTM E 472-86

Standard practice for reporting thermoanalytical data

DIN 51005

Thermische Analyse, Begriffe

5.   Determination of the pour point

NBN 52014

Echantillonnage et analyse des produits du pétrole: Point de trouble et point d'écoulement limite — Monsterneming en ontleding van aardolieproducten: Troebelingspunt en vloeipunt

ASTM D 97-66

Standard test method for pour point of petroleum oils

ISO 3016

Petroleum oils — Determination of pour point

A.2.   BOILING TEMPERATURE

1.   METHOD

The majority of the methods described are based on the OECD Test Guideline (1). The fundamental principles are given in references (2) and (3).

1.1.   INTRODUCTION

The methods and devices described here can be applied to liquid and low melting substances, provided that these do not undergo chemical reaction below the boiling temperature (for example: auto-oxidation, rearrangement, degradation, etc.). The methods can be applied to pure and to impure liquid substances.

Emphasis is put on the methods using photocell detection and thermal analysis, because these methods allow the determination of melting as well as boiling temperatures. Moreover, measurements can be performed automatically.

The ‘dynamic method’ has the advantage that it can also be applied to the determination of the vapour pressure and it is not necessary to correct the boiling temperature to the normal pressure (101,325 kPa) because the normal pressure can be adjusted during the measurement by a manostat.

Remarks:

The influence of impurities on the determination of the boiling temperature depends greatly upon the nature of the impurity. When there are volatile impurities in the sample, which could affect the results, the substance may be purified.

1.2.   DEFINITIONS AND UNITS

The normal boiling temperature is defined as the temperature at which the vapour pressure of a liquid is 101,325 kPa.

If the boiling temperature is not measured at normal atmospheric pressure, the temperature dependence of the vapour pressure can be described by the Clausius-Clapeyron equation:

Formula

where:

p

=

the vapour pressure of the substance in pascals

Δ Hv

=

its heat of vaporisation in J mol-1

R

=

the universal molar gas constant = 8,314 J mol-1 K-1

T

=

thermodynamic temperature in K

The boiling temperature is stated with regard to the ambient pressure during the measurement.

Conversions

Pressure (units: kPa)

100 kPa

=

1 bar = 0,1 MPa

(‘bar’ is still permissible but not recommended)

133 Pa

=

1 mm Hg = 1 Torr

(the units ‘mm Hg’ and ‘Torr’ are not permitted)

1 atm

=

standard atmosphere = 101 325 Pa

(the unit ‘atm’ is not permitted)

Temperature (units: K)

t = T - 273,15

t

:

Celsius temperature, degree Celsius (oC)

T

:

thermodynamic temperature, kelvin (K)

1.3.   REFERENCE SUBSTANCES

Reference substances do not need to be employed in all cases when investigating a new substance. They should primarily serve to check the performance of the method from time to time and to allow comparison with results from other methods.

Some calibration substances can be found in the methods listed in the Appendix.

1.4.   PRINCIPLE OF THE TEST METHOD

Five methods for the determination of the boiling temperature (boiling range) are based on the measurement of the boiling temperature, two others are based on thermal analysis.

1.4.1.   Determination by use of the ebulliometer

Ebulliometers were originally developed for the determination of the molecular weight by boiling temperature elevation, but they are also suited for exact boiling temperature measurements. A very simple apparatus is described in ASTM D 1120-72 (see Appendix). The liquid is heated in this apparatus under equilibrium conditions at atmospheric pressure until it is boiling.

1.4.2.   Dynamic method

This method involves the measurement of the vapour recondensation temperature by means of an appropriate thermometer in the reflux while boiling. The pressure can be varied in this method.

1.4.3.   Distillation method for boiling temperature

This method involves distillation of the liquid and measurement of the vapour recondensation temperature and determination of the amount of distillate.

1.4.4.   Method according to Siwoloboff

A sample is heated in a sample tube, which is immersed in a liquid in a heat-bath. A fused capillary, containing an air bubble in the lower part, is dipped in the sample tube.

1.4.5.   Photocell detection

Following the principle according to Siwoloboff, automatic photo-electrical measurement is made using rising bubbles.

1.4.6.   Differential thermal analysis

This technique records the difference in temperatures between the substance and a reference material as a function of temperature, while the substance and reference material are subjected to the same controlled temperature programme. When the sample undergoes a transition involving a change of enthalpy, that change is indicated by an endothermic departure (boiling) from the base line of the temperature record.

1.4.7.   Differential scanning calorimetry

This technique records the difference in energy inputs into a substance and a reference material as a function of temperature, while the substance and reference material are subjected to the same controlled temperature programme. This energy is the energy necessary to establish zero temperature difference between the substance and the reference material. When the sample undergoes a transition involving a change of enthalpy, that change is indicated by an endothermic departure (boiling) from the base line of the heat flow record.

1.5.   QUALITY CRITERIA

The applicability and accuracy of the different methods used for the determination of the boiling temperature/boiling range are listed in table 1.

Table 1:

Comparison of the methods

Method of measurement

Estimated accuracy

Existing standard

Ebulliometer

±1,4  K (up to 373 K) (5)  (6)

±2,5  K (up to 600 K) (5)  (6)

ASTM D 1120-72 (5)

Dynamic method

±0,5  K (up to 600 K) (6)

 

Distillation process (boiling range)

±0,5  K (up to 600 K)

ISO/R 918, DIN 53171, BS 4591/71

According to Siwoloboff

± 2 K (up to 600 K) (6)

 

Photocell detection

±0,3  K (up to 373 K) (6)

 

Differential thermal calorimetry

±0,5  K (up to 600 K)

±2,0  K (up to 1 273  K)

ASTM E 537-76

Differential scanning calorimetry

±0,5  K (up to 600 K)

±2,0  K (up to 1 273  K)

ASTM E 537-76

1.6.   DESCRIPTION OF THE METHODS

The procedures of some test methods have been described in international and national standards (see Appendix).

1.6.1.   Ebulliometer

See Appendix.

1.6.2.   Dynamic method

See test method A.4 for the determination of the vapour pressure.

The boiling temperature observed with an applied pressure of 101,325 kPa is recorded.

1.6.3.   Distillation process (boiling range)

See Appendix.

1.6.4.   Method according to Siwoloboff

The sample is heated in a melting temperature apparatus in a sample tube, with a diameter of approximately 5 mm (figure 1).

Figure 1 shows a type of standardised melting and boiling temperature apparatus (JIS K 0064) (made of glass, all specifications in millimetres).

Figure 1

Image 4

A: Measuring vessel

B: Stopper

C: Vent

D: Thermometer

E: Auxiliary thermometer

F: Bath liquid

G: Sample tube, maximum 5 mm outer diameter; containing a capillary tube, approximately 100 mm long, approximately 1 mm long inner diameter and approximately 0,2 to 0,3 mm wall-thickness

H: Side tube

A capillary tube (boiling capillary) which is fused about 1 cm above the lower end is placed in the sample tube. The level to which the test substance is added is such that the fused section of the capillary is below the surface of the liquid. The sample tube containing the boiling capillary is fastened either to the thermometer with a rubber band or is fixed with a support from the side (see figure 2).

Figure 2

Principle according to Siwoloboff

Figure 3

Modified principle

Image 5

Image 6

The bath liquid is chosen according to boiling temperature. At temperatures up to 573 K, silicone oil can be used. Liquid paraffin may only be used up to 473 K. The heating of the bath liquid should be adjusted to a temperature rise of 3 K/min at first. The bath liquid must be stirred. At about 10 K below the expected boiling temperature, the heating is reduced so that the rate of temperature rise is less than 1 K/min. Upon approach of the boiling temperature, bubbles begin to emerge rapidly from the boiling capillary.

The boiling temperature is that temperature when, on momentary cooling, the string of bubbles stops and fluid suddenly starts rising in the capillary. The corresponding thermometer reading is the boiling temperature of the substance.

In the modified principle (figure 3) the boiling temperature is determined in a melting temperature capillary. It is stretched to a fine point about 2 cm in length (a) and a small amount of the sample is sucked up. The open end of the fine capillary is closed by melting, so that a small air bubble is located at the end. While heating in the melting temperature apparatus (b), the air bubble expands. The boiling temperature corresponds to the temperature at which the substance plug reaches the level of the surface of the bath liquid (c).

1.6.5.   Photocell detection

The sample is heated in a capillary tube inside a heated metal block.

A light beam is directed, via suitable holes in the block, through the substance onto a precisely calibrated photocell.

During the increase of the sample temperature, single air bubbles emerge from the boiling capillary. When the boiling temperature is reached the number of bubbles increases greatly. This causes a change in the intensity of light, recorded by a photocell, and gives a stop signal to the indicator reading out the temperature of a platinum resistance thermometer located in the block.

This method is especially useful because it allows determinations below room temperature down to 253,15 K (– 20 oC) without any changes in the apparatus. The instrument merely has to be placed in a cooling bath.

1.6.6.   Thermal analysis

1.6.6.1.   Differential thermal analysis

See Appendix.

1.6.6.2.   Differential scanning calorimetry

See Appendix.

2.   DATA

At small deviations from the normal pressure (max. ± 5 kPa) the boiling temperatures are normalised to Tn by means of the following number-value equation by Sidney Young:

Tn = T + (fT × Δp)

where:

Δp

=

(101,325 - p) [note sign]

P

=

pressure measurement in kPa

fT

=

rate of change of boiling temperature with pressure in K/kPa

T

=

measured boiling temperature in K

Tn

=

boiling temperature corrected to normal pressure in K

The temperature-correction factors, fT, and equations for their approximation are included in the international and national standards mentioned above for many substances.

For example, the DIN 53171 method mentions the following rough corrections for solvents included in paints:

Table 2:

Temperature — corrections factors fT

Temperature T (K)

Correction factor fT (K/kPa)

323,15

0,26

348,15

0,28

373,15

0,31

398,15

0,33

423,15

0,35

448,15

0,37

473,15

0,39

498,15

0,41

523,15

0,4

548,15

0,45

573,15

0,47

3.   REPORTING

The test report shall, if possible, include the following information:

method used,

precise specification of the substance (identity and impurities) and preliminary purification step, if any,

an estimate of the accuracy.

The mean of at least two measurements which are in the range of the estimated accuracy (see table 1) is reported as the boiling temperature.

The measured boiling temperatures and their mean shall be stated and the pressure(s) at which the measurements were made shall be reported in kPa. The pressure should preferably be close to normal atmospheric pressure.

All information and remarks relevant for the interpretation of results have to be reported, especially with regard to impurities and physical state of the substance.

4.   REFERENCES

(1)

OECD, Paris, 1981, Test Guideline 103, Decision of the Council C (81) 30 final.

(2)

IUPAC, B. Le Neindre, B. Vodar, editions. Experimental thermodynamics, Butterworths, London, 1975, vol. II.

(3)

R. Weissberger edition: Technique of organic chemistry, Physical methods of organic chemistry, Third Edition, Interscience Publications, New York, 1959, vol. I, Part I, Chapter VIII.

Appendix

For additional technical details, the following standards may be consulted for example.

1.   Ebulliometer

1.1.

Melting temperature devices with liquid bath

ASTM D 1120-72

Standard test method for boiling point of engine anti-freezes

2.   Distillation process (boiling range)

ISO/R 918

Test Method for Distillation (Distillation Yield and Distillation Range)

BS 4349/68

Method for determination of distillation of petroleum products

BS 4591/71

Method for the determination of distillation characteristics

DIN 53171

Losungsmittel für Anstrichstoffe, Bestimmung des Siedeverlaufes

NF T 20-608

Distillation: détermination du rendement et de l'intervalle de distillation

3.   Differential thermal analysis and differential scanning calorimetry

ASTM E 537-76

Standard method for assessing the thermal stability of chemicals by methods of differential thermal analysis

ASTM E 473-85

Standard definitions of terms relating to thermal analysis

ASTM E 472-86

Standard practice for reporting thermoanalytical data

DIN 51005

Thermische Analyse, Begriffe

A.3.   RELATIVE DENSITY

1.   METHOD

The methods described are based on the OECD Test Guideline (1). The fundamental principles are given in reference (2).

1.1.   INTRODUCTION

The methods for determining relative density described are applicable to solid and to liquid substances, without any restriction in respect to their degree of purity. The various methods to be used are listed in table 1.

1.2.   DEFINITIONS AND UNITS

The relative density D20 4 of solids or liquids is the ratio between the mass of a volume of substance to be examined, determined at 20 oC, and the mass of the same volume of water, determined at 4 oC. The relative density has no dimension.

The density, ρ, of a substance is the quotient of the mass, m, and its volume, v.

The density, ρ, is given, in SI units, in kg/m3.

1.3.   REFERENCE SUBSTANCES (1) (3)

Reference substances do not need to be employed in all cases when investigating a new substance. They should primarily serve to check the performance of the method from time to time and to allow comparison with results from other methods.

1.4.   PRINCIPLE OF THE METHODS

Four classes of methods are used.

1.4.1.   Buoyancy methods

1.4.1.1.   Hydrometer (for liquid substances)

Sufficiently accurate and quick determinations of density may be obtained by the floating hydrometers, which allow the density of a liquid to be deduced from the depth of immersion by reading a graduated scale.

1.4.1.2.   Hydrostatic balance (for liquid and solid substances)

The difference between the weight of a test sample measured in air and in a suitable liquid (e.g. water) can be employed to determine its density.

For solids, the measured density is only representative of the particular sample employed. For the determination of density of liquids, a body of known volume, v, is weighed first in air and then in the liquid.

1.4.1.3.   Immersed body method (for liquid substances) (4)

In this method, the density of a liquid is determined from the difference between the results of weighing the liquid before and after immersing a body of known volume in the test liquid.

1.4.2.   Pycnometer methods

For solids or liquids, pycnometers of various shapes and with known volumes may be employed. The density is calculated from the difference in weight between the full and empty pycnometer and its known volume.

1.4.3.   Air comparison pycnometer (for solids)

The density of a solid in any form can be measured at room temperature with the gas comparison pycnometer. The volume of a substance is measured in air or in an inert gas in a cylinder of variable calibrated volume. For the calculation of density one mass measurement is taken after concluding the volume measurement.

1.4.4.   Oscillating densitimeter (5) (6) (7)

The density of a liquid can be measured by an oscillating densitimeter. A mechanical oscillator constructed in the form of a U-tube is vibrated at the resonance frequency of the oscillator which depends on its mass. Introducing a sample changes the resonance frequency of the oscillator. The apparatus has to be calibrated by two liquid substances of known densities. These substances should preferably be chosen such that their densities span the range to be measured.

1.5.   QUALITY CRITERIA

The applicability of the different methods used for the determination of the relative density is listed in the table.

1.6.   DESCRIPTION OF THE METHODS

The standards given as examples, which are to be consulted for additional technical details, are attached in the Appendix.

The tests have to be run at 20 oC, and at least two measurements performed.

2.   DATA

See standards.

3.   REPORTING

The test report shall, if possible, include the following information:

method used,

precise specification of the substance (identity and impurities) and preliminary purification step, if any.

The relative density,

Formula
, shall be reported as defined in 1.2, along with the physical state of the measured substance.

All information and remarks relevant for the interpretation of results have to be reported, especially with regard to impurities and physical state of the substance.

Table:

Applicability of methods

Method of measurement

Density

Maximum possible dynamic viscosity

Existing Standards

solid

liquid

1.4.1.1.

Hydrometer

 

yes

5 Pa s

ISO 387,

ISO 649-2,

NF T 20-050

1.4.1.2.

Hydrostatic balance

 

 

 

 

(a)

solids

yes

 

 

ISO 1183 (A)

(b)

liquids

 

yes

5 Pa s

ISO 901 and 758

1.4.1.3.

Immersed body method

 

yes

20 Pa s

DIN 53217

1.4.2.

Pycnometer

 

 

 

ISO 3507

(a)

solids

yes

 

 

ISO 1183(B),

NF T 20-053

(b)

liquids

 

yes

500 Pa s

ISO 758

1.4.3.

Air comparison pycnometer

yes

 

 

DIN 55990 Teil 3,

DIN 53243

1.4.4.

Oscillating densitimer

 

yes

5 Pa s

 

4.   REFERENCES

(1)

OECD, Paris, 1981, Test Guideline 109, Decision of the Council C(81) 30 final.

(2)

R. Weissberger ed., Technique of Organic Chemistry, Physical Methods of Organic Chemistry, 3rd ed., Chapter IV, Interscience Publ., New York, 1959, vol. I, Part 1.

(3)

IUPAC, Recommended reference materials for realization of physico-chemical properties, Pure and applied chemistry, 1976, vol. 48, p. 508.

(4)

Wagenbreth, H., Die Tauchkugel zur Bestimmung der Dichte von Flüssigkeiten, Technisches Messen tm, 1979, vol. II, p. 427-430.

(5)

Leopold, H., Die digitale Messung von Flüssigkeiten, Elektronik, 1970, vol. 19, p. 297-302.

(6)

Baumgarten, D., Füllmengenkontrolle bei vorgepackten Erzeugnissen -Verfahren zur Dichtebestimmung bei flüssigen Produkten und ihre praktische Anwendung, Die Pharmazeutische Industrie, 1975, vol. 37, p. 717-726.

(7)

Riemann, J., Der Einsatz der digitalen Dichtemessung im Brauereilaboratorium, Brauwissenschaft, 1976, vol. 9, p. 253-255.

Appendix

For additional technical details, the following standards may be consulted for example.

1.   Buoyancy methods

1.1.   Hydrometer

DIN 12790, ISO 387

Hydrometer; general instructions

DIN 12791

Part I: Density hydrometers; construction, adjustment and use

Part II: Density hydrometers; standardised sizes, designation

Part III: Use and test

ISO 649-2

Laboratory glassware: Density hydrometers for general purpose

NF T 20-050

Chemical products for industrial use — Determination of density of liquids — Areometric method

DIN 12793

Laboratory glassware: range find hydrometers

1.2.   Hydrostatic balance

For solid substances

ISO 1183

Method A: Methods for determining the density and relative density of plastics excluding cellular plastics

NF T 20-049

Chemical products for industrial use — Determination of the density of solids other than powders and cellular products — Hydrostatic balance method

ASTM-D-792

Specific gravity and density of plastics by displacement

DIN 53479

Testing of plastics and elastomers; determination of density

For liquid substances

ISO 901

ISO 758

DIN 51757

Testing of mineral oils and related materials; determination of density

ASTM D 941-55, ASTM D 1296-67 and ASTM D 1481-62

ASTM D 1298

Density, specific gravity or API gravity of crude petroleum and liquid petroleum products by hydrometer method

BS 4714

Density, specific gravity or API gravity of crude petroleum and liquid petroleum products by hydrometer method

1.3.   Immersed body method

DIN 53217

Testing of paints, varnishes and similar coating materials; determination of density; immersed body method

2.   Pycnometer methods

2.1.   For liquid substances

ISO 3507

Pycnometers

ISO 758

Liquid chemical products; determination of density at 20 oC

DIN 12797

Gay-Lussac pycnometer (for non-volatile liquids which are not too viscous)

DIN 12798

Lipkin pycnometer (for liquids with a kinematic viscosity of less than 100 10-6 m2 s-1 at 15 oC)

DIN 12800

Sprengel pycnometer (for liquids as DIN 12798)

DIN 12801

Reischauer pycnometer (for liquids with a kinematic viscosity of less than 100. 10-6 m2 s-1 at 20 oC, applicable in particular also to hydrocarbons and aqueous solutions as well as to liquids with higher vapour pressure, approximately 1 bar at 90 oC)

DIN 12806

Hubbard pycnometer (for viscous liquids of all types which do not have too high a vapour pressure, in particular also for paints, varnishes and bitumen)

DIN 12807

Bingham pycnometer (for liquids, as in DIN 12801)

DIN 12808

Jaulmes pycnometer (in particular for ethanol — water mixture)

DIN 12809

Pycnometer with ground-in thermometer and capillary side tube (for liquids which are not too viscous)

DIN 53217

Testing of paints, varnishes and similar products; determination of density by pycnometer

DIN 51757

Point 7: Testing of mineral oils and related materials; determination of density

ASTM D 297

Section 15: Rubber products — chemical analysis

ASTM D 2111

Method C: Halogenated organic compounds

BS 4699

Method for determination of specific gravity and density of petroleum products (graduated bicapillary pycnometer method)

BS 5903

Method for determination of relative density and density of petroleum products by the capillary — stoppered pycnometer method

NF T 20-053

Chemical products for industrial use — Determination of density of solids in powder and liquids — Pyknometric method

2.2.   For solid substances

ISO 1183

Method B: Methods for determining the density and relative density of plastics excluding cellular plastics

NF T 20-053

Chemical products for industrial use — Determination of density of solids in powder and liquids — Pyknometric method

DIN 19683

Determination of the density of soils

3.   Air comparison pycnometer

DIN 55990

Part 3: Prüfung von Anstrichstoffen und ähnlichen Beschichtungsstoffen; Pulverlack; Bestimmung der Dichte

DIN 53243

Anstrichstoffe; chlorhaltige Polymere; Prüfung

A.4.   VAPOUR PRESSURE

1.   METHOD

The majority of the methods described are based on the OECD Test Guideline (1). The fundamental principles are given in references (2) and (3).

1.1.   INTRODUCTION

It is useful to have preliminary information on the structure, the melting temperature and the boiling temperature of the substance to perform this test.

There is no single measurement procedure applicable to the entire range of vapour pressures. Therefore, several methods are recommended to be used for the measurement of vapour pressure from < 10-4 to 105 Pa.

Impurities will usually affect the vapour pressure, and to an extent which depends greatly upon the kind of impurity.

Where there are volatile impurities in the sample, which could affect the result, the substance may be purified. It may also be appropriate to quote the vapour pressure for the technical material.

Some methods described here use apparatus with metallic parts; this should be considered when testing corrosive substances.

1.2.   DEFINITIONS AND UNITS

The vapour pressure of a substance is defined as the saturation pressure above a solid or liquid substance. At the thermodynamic equilibrium, the vapour pressure of a pure substance is a function of temperature only.

The SI unit of pressure which should be used is the pascal (Pa).

Units which have been employed historically, together with their conversion factors, are:

1 Torr (≡ 1 mm Hg)

= 1,333 × 102 Pa

1 atmosphere

= 1,013 × 105 Pa

1 bar

= 105 Pa

The SI unit of temperature is the kelvin (K).

The universal molar gas constant R is 8,314 J mol-1 K-1

The temperature dependence of the vapour pressure is described by the Clausius-Clapeyron equation:

Formula

where:

p

=

the vapour pressure of the substance in pascals

ΔHv

=

its heat of vaporisation in Jmol-1

R

=

the universal molar gas constant in Jmol-1 K-1

T

=

thermodynamic temperature in K

1.3.   REFERENCE SUBSTANCES

Reference substances do not need to be employed in all cases when investigating a new substance. They should primarily serve to check the performance of the method from time to time and to allow comparison with results from other methods.

1.4.   PRINCIPLE OF THE TEST METHODS

For determining the vapour pressure, seven methods are proposed which can be applied in different vapour pressure ranges. For each method, the vapour pressure is determined at various temperatures. In a limited temperature range, the logarithm of the vapour pressure of a pure substance is a linear function of the inverse of the temperature.

1.4.1.   Dynamic method

In the dynamic method, the boiling temperature which pertains to a specified pressure is measured.

Recommended range:

103 up to 105 Pa.

This method has also been recommended for the determination of normal boiling temperature and is useful for that purpose up to 600 K.

1.4.2.   Static method

In the static process, at thermodynamic equilibrium, the vapour pressure established in a closed system is determined at a specified temperature. This method is suitable for one component and multicomponent solids and liquids.

Recommended range:

10 up to 105 Pa.

This method can also be used in the range 1 to 10 Pa, providing care is taken.

1.4.3.   Isoteniscope

This standardised method is also a static method but is usually not suitable for multicomponent systems. Additional information is available in ASTM method D-2879-86.

Recommended range:

from 100 up to 105 Pa.

1.4.4.   Effusion method: Vapour pressure balance

The quantity of substance leaving a cell per unit time through an aperture of known size is determined under vacuum conditions such that return of substance into the cell is negligible (e.g. by measurement of the pulse generated on a sensitive balance by a vapour jet or by measuring the weight loss).

Recommended range:

10-3 to 1 Pa.

1.4.5.   Effusion method: By loss of weight or by trapping vaporisate

The method is based on the estimation of the mass of test substance flowing out per unit of time of a Knudsen cell (4) in the form of vapour, through a micro-orifice under ultra-vacuum conditions. The mass of effused vapour can be obtained either by determining the loss of mass of the cell or by condensing the vapour at low temperature and determining the amount of volatilised substance using chromatographic analysis. The vapour pressure is calculated by applying the Hertz-Knudsen relation.

Recommended range:

10-3 to 1 Pa.

1.4.6.   Gas saturation method

A stream of inert carrier gas is passed over the substance in such a way that it becomes saturated with its vapour. The amount of material transported by a known amount of carrier gas is measurable either by collection in a suitable trap or by an intrain analytical technique. This is then used to calculate the vapour pressure at a given temperature.

Recommended range:

10-4 to 1 Pa.

This method can also be used in the range 1 to 10 Pa providing care is taken.

1.4.7.   Spinning rotor

In the spinning rotor gauge, the actual measuring element is a small steel ball which is suspended in a magnetic field and rotates with high speed. The gas pressure is deduced from the pressure-dependent slow-down of the steel ball.

Recommended range:

10-4 to 0,5 Pa.

1.5.   QUALITY CRITERIA

The various methods of determining the vapour pressure are compared as to application, repeatability, reproducibility, measuring range, existing standard. This is done in the following table.

Table:

Quality criteria

Measuring Method

Substances

Estimated Repeatability (7)

Estimated Reproducibility (7)

Recommended Range

Existing Standard

solid

liquid

1.4.1.

Dynamic method

Low melting

yes

Up to 25 %

Up to 25 %

103 Pa to 2 × 103 Pa

 

 

 

1 to 5 %

1 to 5 %

2 × 103 Pa to 105 Pa

1.4.2.

Static method

yes

yes

5 to 10 %

5 to 10 %

10 Pa to 105 Pa (8)

NFT 20-048 (5)

1.4.3.

Isoteniscope

yes

yes

5 to 10 %

5 to 10 %

102 Pa to 105 Pa

ASTM-D

2879-86

1.4.4.

Effusion method Vap.Pres.balance

yes

yes

5 to 20 %

5 to 50 %

10-3 Pa to 1 Pa

NFT

20-047(6)

1.4.5.

Effusion method weigt loss

yes

yes

10 to 30 %

10-3 Pa to 1 Pa

1.4.6.

Gas saturation method

yes

yes

10 to 30 %

Up to 50 %

10-4 Pa to 1 Pa (8)

1.4.7.

Spinning rotor method

yes

yes

10 to 20 %

10-4 Pa to 0,5 Pa

1.6.   DESCRIPTION OF THE METHODS

1.6.1.   Dynamic measurement

1.6.1.1.   Apparatus

The measuring apparatus typically consists of a boiling vessel with attached cooler made of glass or metal (figure 1), equipment for measuring the temperature, and equipment for regulating and measuring the pressure. A typical measuring apparatus shown in the drawing is made from heat-resistant glass and is composed of five parts:

The large, partially double-walled tube consists of a ground jacket joint, a cooler, a cooling vessel and an inlet.

The glass cylinder, with a Cottrell ‘pump’, is mounted in the boiling section of the tube and has a rough surface of crushed glass to avoid ‘bumping’ in the boiling process.

The temperature is measured with a suitable temperature sensor (e.g. resistance thermometer, jacket thermocouple) immersed in the apparatus to the point of measurement (No 5, figure 1) through a suitable inlet (e.g. male ground joint).

The necessary connections are made to the pressure regulation and measuring equipment.

The bulb, which acts as a buffer volume, is connected with the measuring apparatus by means of a capillary tube.

The boiling vessel is heated by a heating element (e.g. cartridge heater) inserted into the glass apparatus from below. The heating current required is set and regulated via a thermocouple.

The necessary vacuum of between 102 Pa and approximately 105 Pa is produced with a vacuum pump.

A suitable valve is used to meter air or nitrogen for pressure regulation (measuring range approximately 102 to 105 Pa) and ventilation.

Pressure is measured with a manometer.

1.6.1.2.   Measurement procedure

The vapour pressure is measured by determining the boiling temperature of the sample at various specified pressures between roughly 103 and 105 Pa. A steady temperature under constant pressure indicates that the boiling temperature has been reached. Frothing substances cannot be measured using this method.

The substance is placed in the clean, dry sample vessel. Problems may be encountered with non-powder solids but these can sometimes be solved by heating the cooling jacket. Once the vessel has been filled the apparatus is sealed at the flange and the substance degassed. The lowest desired pressure is then set and the heating is switched on. At the same time, the temperature sensor is connected to a recorder.

Equilibrium is reached when a constant boiling temperature is recorded at constant pressure. Particular care must be taken to avoid bumping during boiling. In addition, complete condensation must occur on the cooler. When determining the vapour pressure of low melting solids, care should be taken to avoid the condenser blocking.

After recording this equilibrium point, a higher pressure is set. The process is continued in this manner until 105 Pa has been reached (approximately 5 to 10 measuring points in all). As a check, equilibrium points must be repeated at decreasing pressures.

1.6.2.   Static measurement

1.6.2.1.   Apparatus

The apparatus comprises a container for the sample, a heating and cooling system to regulate the temperature of the sample and measure the temperature. The apparatus also includes instruments to set and measure the pressure. Figures 2a and 2b illustrate the basic principles involved.

The sample chamber (figure 2a) is bounded on one side by a suitable high-vacuum valve. A U-tube containing a suitable manometer fluid is attached to the other side. One end of the U-tube branches off to the vacuum pump, the nitrogen cylinder or ventilation valve, and a manometer.

A pressure gauge with a pressure indicator can be used instead of a U-tube (figure 2b).

In order to regulate the temperature of the sample, the sample vessel together with valve and U-tube or pressure gauge is placed in a bath which is kept at a constant temperature of ±0,2 K. The temperature measurements are taken on the outside wall of the vessel containing the sample or in the vessel itself.

A vacuum pump with an upstream cooling trap is used to evacuate the apparatus.

In method 2a the vapour pressure of the substance is measured indirectly using a zero indicator. This takes into account the fact that the density of the fluid in the U-tube alters if the temperature changes greatly.

The following fluids are suitable for use as zero indicators for the U-tube, depending on the pressure range and the chemical behaviour of the test substance: silicone fluids, phthalates. The test substance must not dissolve noticeably in or react with the U-tube fluid.

For the manometer, mercury can be used in the range of normal air pressure to 102 Pa, while silicone fluids and phthalates are suitable for use below 102 Pa down to 10 Pa. Heatable membrane capacity manometers can even be used at below 10-1 Pa. There are also other pressure gauges which can be used below 102 Pa.

1.6.2.2.   Measurement procedure

Before measuring, all components of the apparatus shown in figure 2 must be cleaned and dried thoroughly.

For method 2a, fill the U-tube with the chosen liquid, which must be degassed at an elevated temperature before readings are taken.

The test substance is placed in the apparatus, which is then closed and the temperature is reduced sufficiently for degassing. The temperature must be low enough to ensure that the air is sucked out, but — in the case of multiple component system — it must not alter the composition of the material. If required, equilibrium can be established more quickly by stirring.

The sample can be supercooled with e.g. liquid nitrogen (taking care to avoid condensation of air or pump fluid) or a mixture of ethanol and dry ice. For low-temperature measurements use a temperature-regulated bath connected to an ultra-cryomat.

With the valve over the sample vessel open, suction is applied for several minutes to remove the air. The valve is then closed and the temperature of the sample reduced to the lowest level desired. If necessary, the degassing operation must be repeated several times.

When the sample is heated the vapour pressure increases. This alters the equilibrium of the fluid in the U-tube. To compensate for this, nitrogen or air is admitted to the apparatus via a valve until the pressure indicator fluid is at zero again. The pressure required for this can be read off a precision manometer at room temperature. This pressure corresponds to the vapour pressure of the substance at that particular measuring temperature.

Method 2b is similar but the vapour pressure is read off directly.

The temperature-dependence of vapour pressure is determined at suitably small intervals (approximately 5 to 10 measuring points in all) up to the desired maximum. Low-temperature readings must be repeated as a check.

If the values obtained from the repeated readings do not coincide with the curve obtained for increasing temperature, this may be due to one of the following:

1.

the sample still contains air (e.g. high-viscosity materials) or low-boiling substances, which is/are released during heating and can be removed by suction following further supercooling;

2.

the cooling temperature is not low enough. In this case liquid nitrogen is used as the cooling agent.

If either l or 2 is the case, the measurements must be repeated;

3.

the substance undergoes a chemical reaction in the temperature range investigated (e.g. decomposition, polymerisation).

1.6.3.   Isoteniscope

A complete description of this method can be found in reference 7. The principle of the measuring device is shown in figure 3. Similarly to the static method described in 1.6.2, the isoteniscope is appropriate for the investigation of solids or liquids.

In the case of liquids, the substance itself serves as the fluid in the auxiliary manometer. A quantity of the liquid, sufficient to fill the bulb and the short leg of the manometer section, is put in the isoteniscope. The isoteniscope is attached to a vacuum system and evacuated, then filled by nitrogen. The evacuation and purge of the system is repeated twice to remove residual oxygen. The filled isoteniscope is placed in an horizontal position so that the sample spreads out into a thin layer in the sample bulb and manometer section (U-part). The pressure of the system is reduced to 133 Pa and the sample gently warmed until it just boils (removal of dissolved fixed gases). The isoteniscope is then placed so that the sample returns to the bulb and short leg of the manometer, so that both are entirely filled with liquid. The pressure is maintained as for degassing; the drawn-out tip of the sample bulb is heated with a small flame until sample vapour released expands sufficiently to displace part of the sample from the upper part of the bulb and manometer arm into the manometer section of the isoteniscope, creating a vapour-filled, nitrogen-free space.

The isoteniscope is then placed in a constant temperature bath, and the pressure of nitrogen is adjusted until its pressure equals that of the sample. Pressure balance is indicated by the manometer section of the isoteniscope. At the equilibrium, the vapour pressure of nitrogen equals the vapour pressure of the substance.

In the case of solids, depending on the pressure and temperature range, the manometer liquids listed in 1.6.2.1 are used. The degassed manometer liquid is filled into a bulge on the long arm of the isoteniscope. Then the solid to be investigated is placed in the bulb and is degassed at elevated temperature. After that the isoteniscope is inclined so that the manometer liquid can flow into the U-tube. The measurement of vapour pressure as a function of temperature is done according to 1.6.2.

1.6.4.   Effusion method: vapour pressure balance

1.6.4.1.   Apparatus

Various versions of the apparatus are described in the literature (1). The apparatus described here illustrates the general principle involved (figure 4). Figure 4 shows the main components of the apparatus, comprising a high-vacuum stainless steel or glass container, equipment to produce and measure a vacuum and built-in components to measure the vapour pressure on a balance. The following built-in components are included in the apparatus:

an evaporator furnace with flange and rotary inlet. The evaporator furnace is a cylindrical vessel, made of e.g. copper or a chemically resistant alloy with good thermal conductivity. A glass vessel with a copper wall can also be used. The furnace has a diameter of approximately 3 to 5 cm and is 2 to 5 cm high. There are between one and three openings of different sizes for the vapour stream. The furnace is heated either by a heating spiral around the outside. To prevent heat being dissipated to the base plate, the heater is attached to the base plate by a metal with low thermal conductivity (nickel-silver or chromium-nickel steel), e.g. a nickel-silver pipe attached to a rotary inlet if using a furnace with several openings. This arrangement has the advantage of allowing the introduction of a copper bar. This allows cooling from the outside using a cooling bath,

if the copper furnace lid has three openings of different diameters at 90o to each other, various vapour pressure ranges within the overall measuring range can be covered (openings between approximately 0,30 and 4,50 mm diameter). Large openings are used for low vapour pressure and vice versa. By rotating the furnace the desired opening or an intermediate position in the vapour stream (furnace opening — shield — balance pan) can be set and the stream of molecules is released or deflected through the furnace opening onto the scale pan. In order to measure the temperature of the substance, a thermocouple or resistance thermometer is placed at a suitable point,

above the shield is a balance pan belonging to a highly sensitive microbalance (see below). The balance pan is approximately 30 mm in diameter. Gold-plated aluminium is a suitable material,

the balance pan is surrounded by a cylindrical brass or copper refrigeration box. Depending on the type of balance, it has openings for the balance beam and a shield opening for the stream of molecules and should guarantee complete condensation of the vapour on the balance pan. Heat dissipation to the outside is ensured e.g. by a copper bar connected to the refrigeration box. The bar is routed through the base plate and thermally insulated from it, e.g. with a chromium-nickel steel tube. The bar is immersed in a Dewar flask containing liquid nitrogen under the base plate or liquid nitrogen is circulated through the bar. The refrigeration box is thus kept at approximately - 120 oC. The balance pan is cooled exclusively by radiation and is satisfactory for the pressure range under investigation (cooling approximately 1 hour before the start of measurement),

the balance is positioned above the refrigeration box. Suitable balances are e.g. a highly sensitive 2-arm electronic microbalance (8) or a highly sensitive moving coil instrument (see OECD Test Guideline 104, Edition 12.05.81),

the base plate also incorporates electrical connections for thermocouples (or resistance thermometers) and heating coils,

a vacuum is produced in the vessel using a partial vacuum pump or high-vacuum pump (required vacuum approximately 1 to 2 × 10-3 Pa, obtained after 2 h pumping). The pressure is regulated with a suitable ionisation manometer.

1.6.4.2.   Measurement procedure

The vessel is filled with the test substance and the lid is closed. The shield and refrigeration box are slid across the furnace. The apparatus is closed and the vacuum pumps are switched on. The final pressure before starting to take measurements should be approximately 10-4 Pa. Cooling of the refrigeration box starts at 10-2 Pa.

Once the required vacuum has been obtained, start the calibration series at the lowest temperature required. The corresponding opening in the lid is set, the vapour stream passes through the shield directly above the opening and strikes the cooled balance pan. The balance pan must be big enough to ensure that the entire stream guided through the shield strikes it. The momentum of the vapour stream acts as a force against the balance pan and the molecules condense on its cool surface.

The momentum and simultaneous condensation produce a signal on the recorder. Evaluation of the signals provides two pieces of information:

1.

in the apparatus described here the vapour pressure is determined directly from the momentum on the balance pan (it is not necessary to know the molecular weight for this (2)). Geometrical factors such as the furnace opening and the angle of the molecular stream must be taken into account when evaluating the readings;

2.

the mass of the condensate can be measured at the same time and the rate of evaporation can be calculated from this. The vapour pressure can also be calculated from the rate of evaporation and molecular weight using the Hertz equation (2).

Formula

where

G

=

evaporation rate (kg s-1 m-2)

M

=

molar mass (g mol-1)

T

=

temperature (K)

R

=

universal molar gas constant (Jmol-1 K-1)

p

=

vapour pressure (Pa)

After the necessary vacuum is reached, the series of measurements is commenced at the lowest desired measuring temperature.

For further measurements, the temperature is increased by small intervals until the maximum desired temperature value is reached. The sample is then cooled again and a second curve of the vapour pressure may be recorded. If the second run fails to confirm the results of the first run, then it is possible that the substance may be decomposing in the temperature range being measured.

1.6.5.   Effusion method — by loss of weight

1.6.5.1.   Apparatus

The effusion apparatus consists of the following basic parts:

a tank that can be thermostated and evacuated and in which the effusion cells are located,

a high vacuum pump (e.g. diffusion pump or turbomolecular pump) with vacuum gauge,

a trap, using liquefied nitrogen or dry ice.

An electrically heated, aluminium vacuum tank with four stainless steel effusion cells is shown in figure 5 for example. The stainless steel foil of about 0,3 mm thickness has an effusion orifice of 0,2 to 1,0 mm diameter and is attached to the effusion cell by a threaded lid.

1.6.5.2.   Measurement procedure

The reference and test substances are filled into each effusion cell, the metal diaphragm with the orifice is secured by the threaded lid, and each cell is weighed to within an accuracy of 0,1 mg. The cell is placed in the thermostated apparatus, which is then evacuated to below one tenth of the expected pressure. At defined intervals of time ranging from 5 to 30 hours, air is admitted into the apparatus, and the loss in mass of the effusion cell is determined by reweighing.

In order to ensure that the results are not influenced by volatile impurities, the cell is reweighed at defined time intervals to check that the evaporation rate is constant over at least two such intervals of time.

The vapour pressure p in the effusion cell is given by:

Formula

where

p

=

vapour pressure (Pa)

m

=

mass of the substance leaving the cell during time t (kg)

t

=

time (s)

A

=

area of the hole (m2)

K

=

correction factor

R

=

universal gas constant (Jmol-1 K-1)

T

=

temperature (K)

M

=

molecular mass (kg mol-1)

The correction factor K depends on the ratio of length to radius of the cylindrical orifice:

ratio

0,1

0,2

0,6

1,0

2,0

K

0,952

0,909

0,771

0,672

0,514

The above equation may be written:

Formula

where:

Formula
and is the effusion cell constant.

This effusion cell constant E may be determined with reference substances (2,9), using the following equation:

Formula

where:

p(r)

=

vapour pressure of the reference substance (Pa)

M(r)

=

molecular mass of the reference substance (kg × mol-1)

1.6.6.   Gas saturation method

1.6.6.1.   Apparatus

A typical apparatus used to perform this test comprises a number of components given in figure 6a and described below (1).

Inert gas:

The carrier gas must not react chemically with the test substance. Nitrogen is usually sufficient for this purpose but occasionally other gases may be required (10). The gas employed must be dry (see figure 6a, key 4: relative humidity sensor).

Flow control:

A suitable gas-control system is required to ensure a constant and selected flow through the saturator column.

Traps to collect vapour:

These are dependent on the particular sample characteristics and the chosen method of analysis. The vapour should be trapped quantitatively and in a form which permits subsequent analysis. For some test substances, traps containing liquids such as hexane or ethylene glycol will be suitable. For others, solid absorbents may be applicable.

As an alternative to vapour trapping and subsequent analysis, in-train analytical techniques, like chromatography, may be used to determine quantitatively the amount of material transported by a known amount of carrier gas. Furthermore, the loss of mass of the sample can be measured.

Heat exchanger:

For measurements at different temperatures it may be necessary to include a heat-exchanger in the assembly.

Saturator column:

The test substance is deposited from a solution onto a suitable inert support. The coated support is packed into the saturator column, the dimensions of which and the flow rate should be such that complete saturation of the carrier gas is ensured. The saturator column must be thermostated. For measurements above room temperature, the region between the saturator column and the traps should be heated to prevent condensation of the test substance.

In order to lower the mass transport occurring by diffusion, a capillary may be placed after the saturator column (figure 6b).

1.6.6.2.   Measurement procedure

Preparation of the saturator column:

A solution of the test substance in a highly volatile solvent is added to a suitable amount of support. Sufficient test substance should be added to maintain saturation for the duration of the test. The solvent is totally evaporated in air or in a rotary evaporator, and the thoroughly mixed material is added to the saturator column. After thermostating the sample, dry nitrogen is passed through the apparatus.

Measurement:

The traps or in-train detector are connected to the column effluent line and the time recorded. The flow rate is checked at the beginning and at regular intervals during the experiment, using a bubble meter (or continuously with a mass flow-meter).

The pressure at the outlet to the saturator must be measured. This may be done either:

(a)

by including a pressure gauge between the saturator and traps (this may not be satisfactory because this increases the dead space and the adsorptive surface); or

(b)

by determining the pressure drops across the particular trapping system used as a function of flow rate in a separate experiment (this may be not very satisfactory for liquid traps).

The time required for collecting the quantity of test substance that is necessary for the different methods of analysis is determined in preliminary runs or by estimates. As an alternative to collecting the substance for further analysis, in-train quantitative analytical technique may be used (e.g. chromatography). Before calculating the vapour pressure at a given temperature, preliminary runs are to be carried out to determine the maximum flow rate that will completely saturate the carrier gas with substance vapour. This is guaranteed if the carrier gas is passed through the saturator sufficiently slowly so that a lower rate gives no greater calculated vapour pressure.

The specific analytical method will be determined by the nature of the substance being tested (e.g. gas chromatography or gravimetry).

The quantity of substance transported by a known volume of carrier gas is determined.

1.6.6.3.   Calculation of vapour pressure

Vapour pressure is calculated from the vapour density, W/V, through the equation:

Formula

where:

p

=

vapour pressure (Pa)

W

=

mass of evaporated test substance (g)

V

=

volume of saturated gas (m3)

R

=

universal molar gas constant (Jmol-1 K-1)

T

=

temperature (K)

M

=

molar mass of test substance (g mol-1)

Measured volumes must be corrected for pressure and temperature differences between the flow meter and the thermostated saturator. If the flow meter is located downstream from the vapour trap, corrections may be necessary to account for any vaporised trap ingredients (1).

1.6.7.   Spinning rotor (8, 11, 13)

1.6.7.1.   Apparatus

The spinning rotor technique can be carried out using a spinning rotor viscosity gauge as shown in figure 8. A schematic drawing of the experimental set-up is shown in figure 7.

The measuring apparatus typically consists of a spinning rotor measuring head, placed in a thermostated enclosure (regulated within 0,1 oC). The sample container is placed in a thermostated enclosure (regulated within 0,01 oC), and all other parts of the set-up are kept at a higher temperature to prevent condensation. A high-vacuum pump device is connected to the system by means of high-vacuum valves.

The spinning rotor measuring head consists of a steel ball (4 to 5 mm diameter) in a tube. The ball is suspended and stabilised in a magnetic field, generally using a combination of permanent magnets and control coils.

The ball is made to spin by rotating fields produced by coils. Pick-up coils, measuring the always present low lateral magnetisation of the ball, allow its spinning rate to be measured.

1.6.7.2.   Measurement procedure

When the ball has reached a given rotational speed v(o) (usually about 400 revolutions per second), further energising is stopped and deceleration takes place, due to gas friction.

The drop of rotational speed is measured as a function of time. As the friction caused by the magnetic suspension is negligible as compared with the gas friction, the gas pressure p is given by:

Formula

where:

Formula

=

average speed of the gas molecules

r

=

radius of the ball

ρ

=

mass density of the ball

σ

=

coefficient of tangential momentum transfer (ε = 1 for an ideal spherical surface of the ball)

t

=

time

v(t)

=

rotational speed after time t

v(o)

=

initial rotational speed

This equation may also be written:

Formula

where tn, tn-1 are the times required for a given number N of revolutions. These time intervals tn and tn-1 succeed one another, and tn > t n-1.

The average speed of the gas molecule

Formula
is given by:

Formula

where:

T

=

temperature

R

=

universal molar gas constant

M

=

molar mass

2.   DATA

The vapour pressure from any of the preceding methods should be determined for at least two temperatures. Three or more are preferred in the range 0 to 50 oC, in order to check the linearity of the vapour pressure curve.

3.   REPORTING

The test report shall, if possible, include the following information:

method used,

precise specification of the substance (identity and impurities) and preliminary purification step, if any,

at least two vapour pressure and temperature values, preferably in the range 0 to 50 oC,

all of the raw data,

a log p versus 1/T curve,

an estimate of the vapour pressure at 20 or 25 oC.

If a transition (change of state, decomposition) is observed, the following information should be noted:

nature of the change,

temperature at which the change occurs at atmospheric pressure,

vapour pressure at 10 and 20 oC below the transition temperature and 10 and 20 oC above this temperature (unless the transition is from solid to gas).

All information and remarks relevant for the interpretation of results have to be reported, especially with regard to impurities and physical state of the substance.

4.   REFERENCES

(1)

OECD, Paris, 1981, Test Guideline 104, Decision of the Council C(81) 30 final.

(2)

Ambrose, D. in B. Le Neindre, B. Vodar, (Eds.): Experimental Thermodynamics, Butterworths, London, 1975, vol. II.

(3)

R. Weissberger ed.: Technique of Organic Chemistry, Physical Methods of Organic Chemistry, 3rd ed. Chapter IX, Interscience Publ., New York, 1959, vol. I, Part I.

(4)

Knudsen, M. Ann. Phys. Lpz., 1909, vol. 29, 1979; 1911, vol. 34, p. 593.

(5)

NF T 20-048 AFNOR (September 85) Chemical products for industrial use — Determination of vapour pressure of solids and liquids within range from 10-1 to 105 Pa — Static method.

(6)

NF T 20-047 AFNOR (September 85) Chemical products for industrial use — Determination of vapour pressure of solids and liquids within range from 10-3 to 1 Pa — Vapour pressure balance method.

(7)

ASTM D 2879-86, Standard test method for vapour pressure-temperature relationship and initial decomposition temperature of liquids by isoteniscope.

(8)

G. Messer, P. Rohl, G. Grosse and W. Jitschin. J. Vac. Sci. Technol.(A), 1987, 'Vol. 5 (4), p. 2440.

(9)

Ambrose, D.; Lawrenson, I.J.; Sprake, C.H.S. J. Chem. Thermodynamics 1975, vol. 7, p. 1173.

(10)

B.F. Rordorf. Thermochimica Acta, 1985, vol. 85, p. 435.

(11)

G. Comsa, J.K. Fremerey and B. Lindenau. J. Vac. Sci. Technol., 1980, vol. 17 (2), p. 642.

(12)

G. Reich. J. Vac. Sci. Technol., 1982, vol. 20 (4), p. 1148.

(13)

J.K. Fremerey. J. Vac. Sci. Technol.(A), 1985, vol. 3 (3), p. 1715.

Appendix 1

Estimation method

INTRODUCTION

Calculated values of the vapour pressure can be used:

for deciding which of the experimental methods is appropriate,

for providing an estimate or limit value in cases where the experimental method cannot be applied due to technical reasons (including where the vapour pressure is very low),

to help identify those cases where omitting experimental measurement is justified because the vapour pressure is likely to be < 10-5 Pa at ambient temperature.

ESTIMATION METHOD

The vapour pressure of liquids and solids can be estimated by use of the modified Watson Correlation (a). The only experimental data required is the normal boiling point. The method is applicable over the pressure range from 105 Pa to 10-5 Pa.

Detailed information on the method is given in ‘Handbook of Chemical Property Estimation Methods’ (b).

CALCULATION PROCEDURE

According to (b) the vapour pressure is calculated as follows:

Formula

where:

T

= temperature of interest

Tb

= normal boiling point

Pvp

= vapour pressure at temperature T

ΔHvb

= heat of vaporisation

ΔZb

= compressibility factor (estimated at 0,97)

m

= empirical factor depending on the physical state at the temperature of interest

further:

Formula

where KF is an empirical factor considering the polarity of the substance. For several compound types, KF factors are listed in reference (b).

Quite often, data are available in which a boiling point at reduced pressure is given. In such a case, according to (b), the vapour pressure is calculated as follows:

Formula

where T1 is the boiling point at the reduced pressure P1.

REPORT

When using the estimation method, the report shall include a comprehensive documentation of the calculation.

LITERATURE

(a)

K.M. Watson, Ind. Eng. Chem., 1943, vol. 35, p. 398.

(b)

W.J. Lyman, W.F. Reehl, D.H. Rosenblatt. Handbook of Chemical Property Estimation Methods, Mc Graw-Hill, 1982.

Appendix 2

Figure 1

Apparatus for determining the vapour pressure curve according to the dynamic method

Image 7

1 = Thermocouple

2 = Vacuum buffer volume

3 = Pressure gauge

4 = Vacuum

5 = Measuring point

6 = Heating element circa 150 W

Figure 2a

Apparatus for determining the vapour pressure curve according to the static method (using a U-tube manometer)