02008R0440 — EN — 18.05.2017 — 007.001

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►B ►C1 COMMISSION 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) ◄ (OJ L 142 31.5.2008, p. 1)

Amended by:





Corrected by:









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COMMISSION 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)

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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.









ANNEX

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Note:

Before using any of the following test methods to test a multi-constituent substance (MCS), a substance of unknown or variable composition, complex reaction product or biological material (UVCB), or a mixture and where its applicability for the testing of MCS, UVCB, or mixtures is not indicated in the respective test method, it should be considered whether the method is adequate for the intended regulatory purpose.

If the test method is used for the testing of a MCS, UVCB or mixture, sufficient information on its composition should be made available, as far as possible, e.g. by the chemical identity of its constituents, their quantitative occurrence, and relevant properties of the constituents.

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

TABLE OF CONTENTS A.1. MELTING/FREEZING TEMPERATURE A.2. BOILING TEMPERATURE A.3. RELATIVE DENSITY A.4. VAPOUR PRESSURE A.5. SURFACE TENSION A.6. WATER SOLUBILITY A.8. PARTITION COEFFICIENT A.9. FLASH-POINT A.10. FLAMMABILITY (SOLIDS) A.11. FLAMMABILITY (GASES) A.12. FLAMMABILITY (CONTACT WITH WATER) A.13. PYROPHORIC PROPERTIES OF SOLIDS AND LIQUIDS A.14. EXPLOSIVE PROPERTIES A.15. AUTO-IGNITION TEMPERATURE (LIQUIDS AND GASES) A.16. RELATIVE SELF-IGNITION TEMPERATURE FOR SOLIDS A.17. OXIDISING PROPERTIES (SOLIDS) A.18. NUMBER — AVERAGE MOLECULAR WEIGHT AND MOLECULAR WEIGHT DISTRIBUTION OF POLYMERS A.19. LOW MOLECULAR WEIGHT CONTENT OF POLYMERS A.20. SOLUTION/EXTRACTION BEHAVIOUR OF POLYMERS IN WATER A.21. OXIDISING PROPERTIES (LIQUIDS) A.22. LENGTH WEIGHTED GEOMETRIC MEAN DIAMETER OF FIBRES A.23. PARTITION COEFFICIENT (1-OCTANOL/WATER): SLOW-STIRRING METHOD A.24. PARTITION COEFFICIENT (N-OCTANOL/WATER), HIGH PERFORMANCELIQUID CHROMATOGRAPHY (HPLC) METHOD A.25. DISSOCIATION CONSTANTS IN WATER (TITRATION METHOD — SPECTROPHOTOMETRIC METHOD — CONDUCTOMETRIC METHOD)

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 (1) Dependent on type of instrument and on degree of purity of the substance.







B. Hot stages and freezing methods Method of measurement Substances which can be pulverised Substances which are not readily pulverised Temperature range Estimated accuracy (1) 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 (1) Dependent on type of instrument and on degree of purity of the substance







C. Thermal analysis Method of measurement Substances which can be pulverised Substances which are not readily pulverised Temperature range Estimated accuracy (1) 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 (1) Dependent on type of instrument and on degree of purity of the substance







D. Pour point Method of measurement Substances which can be pulverised Substances which are not readily pulverised Temperature range Estimated accuracy (1) 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) Dependent on type of instrument and on degree of purity of the substance

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

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.

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.

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.

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.

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

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).

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

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:

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) (1) (2) ± 2,5 K (up to 600 K) (1) (2) ASTM D 1120-72 (1) Dynamic method ± 0,5 K (up to 600 K) (2) 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) (2) Photocell detection ± 0,3 K (up to 373 K) (2) 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) This accuracy is only valid for the simple device as for example described in ASTM D 1120-72; it can be improved with more sophisticated ebulliometer devices. (2) Only valid for pure substances. The use in other circumstances should be justified.

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

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

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,

, 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

▼M1

A.4. VAPOUR PRESSURE

1. METHOD

This method is equivalent to OECD TG 104 (2004).

1.1. INTRODUCTION

This revised version of method A.4(1) includes one additional method; Effusion method: isothermal thermogravimetry, designed for substances with very low pressures (down to 10–10 Pa). In the light of needs for procedures, especially in relation to obtaining vapour pressure for substances with low vapour pressure, other procedures of this method are re-evaluated with respect to other applicability ranges.

At the thermodynamic equilibrium the vapour pressure of a pure substance is a function of temperature only. The fundamental principles are described elsewhere (2)(3).

No single measurement procedure is applicable to the entire range of vapour pressures from less than 10–10 to 105 Pa. Eight methods for measuring vapour pressure are included in this method which can be applied in different vapour pressure ranges. The various methods are compared as to application and measuring range in Table 1. The methods can only be applied for compounds that do not decompose under the conditions of the test. In cases where the experimental methods cannot be applied due to technical reasons, the vapour pressure can also be estimated, and a recommended estimation method is set out in the Appendix.

1.2. DEFINITIONS AND UNITS

The vapour pressure of a substance is defined as the saturation pressure above a solid or liquid substance.

The SI unit of pressure, which is the pascal (Pa), should be used. Other units which have been employed historically are given hereafter, together with their conversion factors:







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 conversion of degrees Celsius to kelvin is according to the formula:

T = t + 273,15

where, T is the kelvin or thermodynamic temperature and t is the Celsius temperature.







Table 1 Measuring method Substances Estimated repeatability Estimated reproducibility Recommended range Solid Liquid Dynamic method Low melting Yes up to 25 % 1 to 5 % up to 25 % 1 to 5 % 103 Pa to 2 × 103 Pa 2 × 103 Pa to 105 Pa Static method Yes Yes 5 to 10 % 5 to 10 % 10 Pa to 105 Pa 10–2 Pa to 105 Pa (1) Isoteniscope method Yes Yes 5 to 10 % 5 to 10 % 102 Pa to 105 Pa Effusion method: vapour pressure balance Yes Yes 5 to 20 % up to 50 % 10–3 to 1 Pa Effusion method: Knudsen cell Yes Yes 10 to 30 % — 10–10 to 1 P Effusion method: isothermal thermogravimetry Yes Yes 5 to 30 % up to 50 % 10–10 to 1 Pa Gas saturation method Yes Yes 10 to 30 % up to 50 % 10–10 to 103 Pa Spinning rotor method Yes Yes 10 to 20 % — 10–4 to 0,5 Pa (1) When using a capacitance manometer

1.3. PRINCIPLE OF THE TEST

In general, 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 thermodynamic temperature according to the simplified Clapeyron-Clausius equation:

where:

p = the vapour pressure in pascals

ΔHv = the heat of vaporisation in J mol–1

R = the universal gas constant, 8,314 J mol–1 K–1

T = the temperature in K

1.4. REFERENCE SUBSTANCES

Reference substances do not need to be employed. They serve primarily to check the performance of a method from time to time as well as to allow comparison between results of different methods.

1.5. DESCRIPTION OF THE METHOD

1.5.1. Dynamic method (Cottrell’s method)

1.5.1.1. Principle

The vapour pressure is determined by measuring the boiling temperature of the substance at various specified pressures between roughly 103 and 105 Pa. This method is also recommended for the determination of the boiling temperature. For that purpose it is useful up to 600 K. The boiling temperatures of liquids are approximately 0,1 °C higher at a depth of 3 to 4 cm than at the surface because of the hydrostatic pressure of the column of liquid. In Cottrell’s method (4) the thermometer is placed in the vapour above the surface of the liquid and the boiling liquid is made to pump itself continuously over the bulb of the thermometer. A thin layer of liquid which is in equilibrium with vapour at atmospheric pressure covers the bulb. The thermometer thus reads the true boiling point, without errors due to superheating or hydrostatic pressure. The pump originally employed by Cottrell is shown in figure 1. Tube A contains the boiling liquid. A platinum wire B sealed into the bottom facilitates uniform boiling. The side tube C leads to a condenser, and the sheath D prevents the cold condensate from reaching the thermometer E. When the liquid in A is boiling, bubbles and liquid trapped by the funnel are poured via the two arms of the pump F over the bulb of the thermometer.







Figure 1 Figure 2

Cottrell pump (4)

A: Thermocouple

B: Vacuum buffer volume

C: Pressure gauge

D: Vacuum

E: Measuring point

F: Heating element c.a. 150 W

1.5.1.2. Apparatus

A very accurate apparatus, employing the Cottrell principle, is shown in figure 2. It consists of a tube with a boiling section in the lower part, a cooler in the middle part, and an outlet and flange in the upper part. The Cottrell pump is placed in the boiling section which is heated by means of an electrical cartridge. The temperature is measured by a jacketed thermocouple, or resistance thermometer inserting through the flange at the top. The outlet is connected to the pressure regulation system. The latter consists of a vacuum pump, a buffer volume, a manostat for admitting nitrogen for pressure regulation and manometer.

1.5.1.3. Procedure

The substance is placed in the boiling section. Problems may be encountered with non-powder solids but these can sometimes be solved by heating the cooling jacket. The apparatus is sealed at the flange and the substance degassed. Frothing substances cannot be measured using this method.

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 prevent the condenser from 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.

1.5.2. Static method

1.5.2.1. Principle

In the static method (5), the vapour pressure at thermodynamic equilibrium is determined at a specified temperature. This method is suitable for substances and multicomponent liquids and solids in the range from 10–1 to 105 Pa and, provided care is taken, also in the range 1 to 10 Pa.

1.5.2.2. Apparatus

The equipment consists of a constant-temperature bath (precision of ± 0,2 K), a container for the sample connected to a vacuum line, a manometer and a system to regulate the pressure. The sample chamber (figure 3a) is connected to the vacuum line via a valve and a differential manometer (U-tube containing a suitable manometer fluid) which serves as zero indicator. Mercury, silicones and phthalates are suitable for use in the differential manometer, depending on the pressure range and the chemical behaviour of the test substance. However, based on environmental concerns, the use of mercury should be avoided, if possible. The test substance must not dissolve noticeably in, or react with, the U-tube fluid. A pressure gauge can be used instead of a U-tube (figure 3b). For the manometer, mercury can be used in the range from normal pressure down to 102 Pa, while silicone fluids and phthalates are suitable for use below 102 Pa down to 10 Pa. There are other pressure gauges which can be used below 102 Pa and heatable membrane capacity manometers can even be used at below 10–1 Pa. The temperature is measured on the outside wall of the vessel containing the sample or in the vessel itself.

1.5.2.3. Procedure

Using the apparatus as described in figure 3a, 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 and degassed at reduced temperature. In the case of a multiple-component sample, the temperature should be low enough to ensure that the composition of the material is not altered. Equilibrium can be established more quickly by stirring. The sample can be cooled with liquid nitrogen or dry ice, but care should be taken to avoid condensation of air or pump-fluid. With the valve over the sample vessel open, suction is applied for several minutes to remove the air. If necessary, the degassing operation is repeated several times.







Figure 3a Figure 3b

When the sample is heated with the valve closed, 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 until the differential pressure indicator is at zero again. The pressure required for this can be read off the manometer or off an instrument of higher precision. This pressure corresponds to the vapour pressure of the substance at the temperature of the measurement. Using the apparatus described in figure 3b, the vapour pressure is read off directly.

The vapour pressure is determined at suitably small temperature intervals (approximately 5 to 10 measuring points in all) up to the desired temperature 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 situations:

(i) the sample still contains air (e.g. in the case of highly viscous materials) or low-boiling substances which is or are released during heating;

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

1.5.3. Isoteniscope Method

1.5.3.1. Principle

The isoteniscope (6) is based on the principle of the static method. The method involves placing a sample in a bulb maintained at constant temperature and connected to a manometer and a vacuum pump. Impurities more volatile than the substance are removed by degassing at reduced pressure. The vapour pressure of the sample at selected temperatures is balanced by a known pressure of inert gas. The isoteniscope was developed to measure the vapour pressure of certain liquid hydrocarbons but it is appropriate for the investigation of solids as well. The method is usually not suitable for multicomponent systems. Results are subject to only slight errors for samples containing non-volatile impurities. The recommended range is 102 to 105 Pa.

1.5.3.2. Apparatus

An example of a measuring device is shown in figure 4. A complete description can be found in ASTM D 2879-86 (6).

1.5.3.3. Procedure

In the case of liquids, the substance itself serves as the fluid in the differential manometer. A quantity of the liquid, sufficient to fill the bulb and the short leg of the manometer, 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 a horizontal position so that the sample spreads out into a thin layer in the sample bulb and manometer. The pressure of the system is reduced to 133 Pa and the sample is gently warmed until it just boils (removal of dissolved gases). The isoteniscope is then placed so that the sample returns to the bulb and fills the short leg of the manometer. The pressure is maintained at 133 Pa. The drawn-out tip of the sample bulb is heated with a small flame until the sample vapour released expands sufficiently to displace part of the sample from the upper part of the bulb and manometer arm into the manometer, creating a vapour-filled, nitrogen-free space. The isoteniscope is then placed in a constant temperature bath, and the pressure of the nitrogen is adjusted until it equals that of the sample. At the equilibrium, the pressure of the nitrogen equals the vapour pressure of the substance.

In the case of solids, and depending on the pressure and temperature ranges, manometer liquids such as silicon fluids or phthalates are used. The degassed manometer liquid is put in a bulge provided on the long arm of the isoteniscope. Then the solid to be investigated is placed in the sample bulb and is degassed at an elevated temperature. After that, the isoteniscope is inclined so that the manometer liquid can flow into the U-tube.

1.5.4. Effusion method: vapour pressure balance (7)

1.5.4.1. Principle

A sample of the test substance is heated in a small furnace and placed in an evacuated bell jar. The furnace is covered by a lid which carries small holes of known diameters. The vapour of the substance, escaping through one of the holes, is directed onto a balance pan of a highly sensitive balance which is also enclosed in the evacuated bell jar. In some designs the balance pan is surrounded by a refrigeration box, providing heat dissipation to the outside by thermal conduction, and is cooled by radiation so that the escaping vapour condenses on it. The momentum of the vapour jet acts as a force on the balance. The vapour pressure can be derived in two ways: directly from the force on the balance pan and also from the evaporation rate using the Hertz-Knudsen equation (2):

where:

G = evaporation rate (kg s–1 m–2)

M = molar mass (g mol–1)

T = temperature (K)

R = universal gas constant (J mol–1 K–1)

P = vapour pressure (Pa)

The recommended range is 10–3 to 1 Pa.

1.5.4.2. Apparatus

The general principle of the apparatus is illustrated in figure 5.







A: Base plate F: Refrigeration box and cooling bar B: Moving coil instrument G: Evaporator furnace C: Bell jar H: Dewar flask with liquid nitrogen D: Balance with scale pan I: Measurement of temperature of sample E: Vacuum measuring device J: Test Substance

1.5.5. Effusion method: Knudsen cell

1.5.5.1. Principle

The method is based on the estimation of the mass of test substance flowing out per unit of time of a Knudsen cell (8) 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 chromatography. The vapour pressure is calculated by applying the Hertz-Knudsen relation (see section 1.5.4.1) with correction factors that depend on parameters of the apparatus (9). The recommended range is 10–10 to 1 Pa (10)(11)(12)(13)(14).

1.5.5.2. Apparatus

The general principle of the apparatus is illustrated in figure 6.







1: Connection to vacuum 7: Threaded lid 2: Wells from platinum resistance thermometer or temperature measurement and control 8: Butterfly nuts 3: Lid for vacuum tank 9: Bolts 4: O-ring 10: Stainless steel effusion cells 5: Aluminum vacuum tank 11: Heater cartridge 6: Device for installing and removing the effusion cells

1.5.6. Effusion method: isothermal thermogravimetry

1.5.6.1. Principle

The method is based on the determination of accelerated evaporation rates for the test substance at elevated temperatures and ambient pressure using thermogravimetry (10)(15)(16)(17)(18)(19)(20). The evaporation rates vT result from exposing the selected compound to a slowly flowing inert gas atmosphere, and monitoring the weight loss at defined isothermal temperatures T in Kelvin over appropriate periods of time. The vapour pressures pT are calculated from the vT values by using the linear relationship between the logarithm of the vapour pressure and the logarithm of the evaporation rate. If necessary, an extrapolation to temperatures of 20 and 25 °C can be made by regression analysis of log pT vs. 1/T. This method is suitable for substances with vapour pressures as low as 10–10 Pa (10–12 mbar) and with purity as close as possible to 100 % to avoid the misinterpretation of measured weight losses.

1.5.6.2. Apparatus

The general principle of the experimental set-up is shown in figure 7.

The sample carrier plate, hanging on a microbalance in a temperature controlled chamber, is swept by a stream of dry nitrogen gas which carries the vaporised molecules of the test substance away. After leaving the chamber, the gas stream is purified by a sorption unit.

1.5.6.3. Procedure

The test substance is applied to the surface of a roughened glass plate as a homogeneous layer. In the case of solids, the plate is wetted uniformly by a solution of the substance in a suitable solvent and dried in an inert atmosphere. For the measurement, the coated plate is hung into the thermogravimetric analyser and subsequently its weight loss is measured continuously as a function of time.

The evaporation rate vT at a definite temperature is calculated from the weight loss Δm of the sample plate by

where F is the surface area of the coated test substances, normally the surface area of the sample plate, and t is the time for weight loss Δm.

The vapour pressure pT is calculated on the basis of its function of evaporation rate vT:

Log pT = C + D · log vT

where C and D are constants specific for the experimental arrangement used, depending on the diameter of the measurement chamber and on the gas flow rate. These constants must be determined once by measuring a set of compounds with known vapour pressure and regressing log pT vs. log vT (11)(21)(22).

The relationship between the vapour pressure pT and the temperature T in Kelvin is given by

Log pT = A + B · 1/T

where A and B are constants obtained by regressing log pT vs. 1/T. With this equation, the vapour pressure can be calculated for any other temperature by extrapolation.

1.5.7. Gas saturation method (23)

1.5.7.1. Principle

Inert gas is passed, at room temperature and at a known flow rate, through or over a sample of the test substance, slowly enough to ensure saturation. Achieving saturation in the gas phase is of critical importance. The transported substance is trapped, generally using a sorbent, and its amount is determined. As an alternative to vapour trapping and subsequent analysis, in-train analytical techniques, like gas chromatography, may be used to determine quantitatively the amount of material transported. The vapour pressure is calculated on the assumption that the ideal gas law is obeyed and that the total pressure of a mixture of gases is equal to the sum of the pressures of the component gases. The partial pressure of the test substance, i.e. the vapour pressure, is calculated from the known total gas volume and from the weight of the material transported.

The gas saturation procedure is applicable to solid or liquid substances. It can be used for vapour pressures down to 10–10 Pa (10)(11)(12)(13)(14). The method is most reliable for vapour pressures below 103 Pa. Above 103 Pa, the vapour pressures are generally overestimated, probably due to aerosol formation. Since the vapour pressure measurements are made at room temperature, the need to extrapolate data from high temperatures is not necessary and high temperature extrapolation, which can often cause serious errors, is avoided.

1.5.7.2. Apparatus

The procedure requires the use of a constant-temperature box. The sketch in figure 8 shows a box containing three solid and three liquid sample holders, which allow for the triplicate analysis of either a solid or a liquid sample. The temperature is controlled to ± 0,5 °C or better.

In general, nitrogen is used as an inert carrier gas but, occasionally, another gas may be required (24). The carrier gas must be dry. The gas stream is split into 6 streams, controlled by needle valves (approximately 0,79 mm orifice), and flows into the box via 3,8 mm i.d. copper tubing. After temperature equilibration, the gas flows through the sample and the sorbent trap and exists from the box.

Solid samples are loaded into 5 mm i.d. glass tubing between glass wool plugs (see Figure 9). Figure 10 shows a liquid sample holder and sorbent system. The most reproducible method for measuring the vapour pressure of liquids is to coat the liquid on glass beads or on an inert sorbent such as silica, and to pack the holder with these beads. As an alternative, the carrier gas may be made to pass a coarse frit and bubble through a column of the liquid test substance.







Figure 9 Figure 10

The sorbent system contains a front and a backup sorbent section. At very low vapour pressures, only small amounts are retained by the sorbent and the adsorption on the glass wool and the glass tubing between the sample and the sorbent may be a serious problem.

Traps cooled with solid CO2 are another efficient way for collecting the vaporised material. They do not cause any back pressure on the saturator column and it is also easy to quantitatively remove the trapped material.

1.5.7.3. Procedure

The flow rate of the effluent carrier gas is measured at room temperature. The flow rate is checked frequently during the experiment to assure that there is an accurate value for the total volume of carrier gas. Continuous monitoring with a mass flow-meter is preferred. Saturation of the gas phase may require considerable contact time and hence quite low gas flow rates (25).

At the end of the experiment, both the front and backup sorbent sections are analysed separately. The compound on each section is desorbed by adding a solvent. The resulting solutions are analysed quantitatively to determine the weight desorbed from each section. The choice of the analytical method (also the choice of sorbent and desorbing solvent) is dictated by the nature of the test material. The desorption efficiency is determined by injecting a known amount of sample onto the sorbent, desorbing it and analysing the amount recovered. It is important to check the desorption efficiency at or near the concentration of the sample under the test conditions.

To assure that the carrier gas is saturated with the test substance, three different gas flow rates are used. If the calculated vapour pressure shows no dependence on flow rate, the gas is assumed to be saturated.

The vapour pressure is calculated through the equation:

where:

p = vapour pressure (Pa)

W = mass of evaporated test substance (g)

V = volume of saturated gas (m3)

R = universal gas constant 8,314 (J mol–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 saturator.

1.5.8. Spinning rotor

1.5.8.1. Principle

This method uses a spinning rotor viscosity gauge, in which the measuring element is a small steel ball which, suspended in a magnetic field, is made to spin by rotating fields (26)(27)(28). Pick-up coils allow its spinning rate to be measured. When the ball has reached a given rotational speed, usually about 400 revolutions per second, energising is stopped and deceleration, due to gas friction, takes place. The drop of rotational speed is measured as a function of time. The vapour pressure is deduced from the pressure-dependent slow-down of the steel ball. The recommended range is 10–4 to 0,5 Pa.

1.5.8.2. Apparatus

A schematic drawing of the experimental set-up is shown in figure 11. The measuring head is placed in a constant-temperature enclosure, regulated within 0,1 °C. The sample container is placed in a separate enclosure, also regulated within 0,1 °C. All other parts of the set-up are kept at a higher temperature to prevent condensation. The whole apparatus is connected to a high-vacuum system.

2. DATA AND REPORTING

2.1. 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 from 0 to 50 °C, in order to check the linearity of the vapour pressure curve. In case of Effusion method (Knudsen cell and isothermal thermogravimetry) and Gas saturation method, 120 to 150 °C is recommended for the measuring temperature range instead of 0 to 50 °C.

2.2. TEST REPORT

The test report must 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 — and preferably three or more — required in the range from 0 to 50 °C (or 120 to 150 °C),

— at least one of the temperatures should be at or below 25 °C, if technically possible according to the chosen method,

— all original data,

— a log p versus 1/T curve,

— an estimate of the vapour pressure at 20 or 25 °C.

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 °C below the transition temperature and 10 and 20 °C 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.

3. LITERATURE

(1) Official Journal of the European Communities L 383 A, 26-47 (1992).

(2) Ambrose, D. (1975). Experimental Thermodynamics, Vol. II, Le Neindre, B., and Vodar, B., Eds., Butterworths, London.

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

(4) Glasstone, S. (1946). Textbook of Physical Chemistry, 2nd ed., Van Nostrand Company, New York.

(5) NF T 20-048 AFNOR (September 1985). Chemical products for industrial use — Determination of vapour pressure of solids and liquids within a range from 10–1 to 105 Pa — Static method.

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

(7) NF T 20-047 AFNOR (September 1985). 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.

(8) Knudsen, M. (1909). Ann. Phys. Lpz., 29, 1979; (1911), 34, 593.

(9) Ambrose, D., Lawrenson, I.J., Sprake, C.H.S. (1975). J. Chem. Thermodynamics 7, 1173.

(10) Schmuckler, M.E., Barefoot, A.C., Kleier, D.A., Cobranchi, D.P. (2000), Vapor pressures of sulfonylurea herbicides; Pest Management Science 56, 521-532.

(11) Tomlin, C.D.S. (ed.), The Pesticide Manual, Twelfth Edition (2000).

(12) Friedrich, K., Stammbach, K., Gas chromatographic determination of small vapour pressures determination of the vapour pressures of some triazine herbicides. J. Chromatog. 16 (1964), 22-28.

(13) Grayson, B.T., Fosbraey, L.A., Pesticide Science 16 (1982), 269-278.

(14) Rordorf, B.F., Prediction of vapor pressures, boiling points and enthalpies of fusion for twenty-nine halogenated dibenzo-p-dioxins, Thermochimia Acta 112 Issue 1 (1987), 117-122.

(15) Gückel, W., Synnatschke, G., Ritttig, R., A Method for Determining the Volatility of Active Ingredients Used in Plant Protection; Pesticide Science 4 (1973) 137-147.

(16) Gückel, W., Synnatschke, G., Ritttig, R., A Method for Determining the Volatility of Active Ingredients Used in Plant Protection II. Application to Formulated Products; Pesticide Science 5 (1974) 393-400.

(17) Gückel, W., Kaestel, R., Lewerenz, J., Synnatschke, G., A Method for Determining the Volatility of Active Ingredients Used in Plant Protection. Part III: The Temperature Relationship between Vapour Pressure and Evaporation Rate; Pesticide Science 13 (1982) 161-168.

(18) Gückel, W., Kaestel, R., Kroehl, T., Parg, A., Methods for Determining the Vapour Pressure of Active Ingredients Used in Crop Protection. Part IV: An Improved Thermogravimetric Determination Based on Evaporation Rate; Pesticide Science 45 (1995) 27-31.

(19) Kroehl, T., Kaestel, R., Koenig, W., Ziegler, H., Koehle, H., Parg, A., Methods for Determining the Vapour Pressure of Active Ingredients Used in Crop Protection. Part V: Thermogravimetry Combined with Solid Phase MicroExtraction (SPME); Pesticide Science, 53 (1998) 300-310.

(20) Tesconi, M., Yalkowsky, S.H., A Novel Thermogravimetric Method for Estimating the Saturated Vapor Pressure of Low-Volatility Compounds; Journal of Pharmaceutical Science 87(12) (1998) 1512-20.

(21) Lide, D.R. (ed.), CRC Handbook of Chemistry and Physics, 81st ed. (2000), Vapour Pressure in the Range — 25 °C to 150 °C.

(22) Meister, R.T. (ed.), Farm Chemicals Handbook, Vol. 88 (2002).

(23) 40 CFR, 796. (1993). pp 148-153, Office of the Federal Register, Washington DC.

(24) Rordorf B.F. (1985). Thermochimica Acta 85, 435.

(25) Westcott et al. (1981). Environ. Sci. Technol. 15, 1375.

(26) Messer G., Röhl, P., Grosse G., and Jitschin W. (1987). J. Vac. Sci. Technol. (A), 5(4), 2440.

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

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

Appendix

Estimation method

INTRODUCTION

Estimated 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.

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). See also OECD Environmental Monograph No.67 (c).

CALCULATION PROCEDURE

The vapour pressure is calculated as follows:

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,

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, the vapour pressure is calculated as follows:

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) Watson, K.M. (1943). Ind. Eng. Chem, 35, 398.

(b) Lyman, W.J., Reehl, W.F., Rosenblatt, D.H. (1982). Handbook of Chemical Property Estimation Methods, McGraw-Hill.

(c) OECD Environmental Monograph No.67. Application of Structure-Activity Relationships to the Estimation of Properties Important in Exposure Assessment (1993).

▼B

A.5. SURFACE TENSION

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 described methods are to be applied to the measurement of the surface tension of aqueous solutions.

It is useful to have preliminary information on the water solubility, the structure, the hydrolysis properties and the critical concentration for micelles formation of the substance before performing these tests.

The following methods are applicable to most chemical substances, without any restriction in respect to their degree of purity.

The measurement of the surface tension by the ring tensiometer method is restricted to aqueous solutions with a dynamic viscosity of less than approximately 200 mPa s.

1.2. DEFINITIONS AND UNITS

The free surface enthalpy per unit of surface area is referred to as surface tension.

The surface tension is given as:

N/m (SI unit) or

mN/m (SI sub-unit)

1 N/m = 103 dynes/cm

1 mN/m = 1 dyne/cm in the obsolete cgs system

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.

Reference substances which cover a wide range of surface tensions are given in references 1 and 3.

1.4. PRINCIPLE OF THE METHODS

The methods are based on the measurement of the maximum force which is necessary to exert vertically, on a stirrup or a ring in contact with the surface of the liquid being examined placed in a measuring cup, in order to separate it from this surface, or on a plate, with an edge in contact with the surface, in order to draw up the film that has formed.

Substances which are soluble in water at least at a concentration of 1 mg/l are tested in aqueous solution at a single concentration.

1.5. QUALITY CRITERIA

These methods are capable of greater precision than is likely to be required for environmental assessment.

1.6. DESCRIPTION OF THE METHODS

A solution of the substance is prepared in distilled water. The concentration of this solution should be 90 % of the saturation solubility of the substance in water; when this concentration exceeds 1 g/l, a concentration of 1 g/l is used for testing. Substances with water solubility lower than 1 mg/l need not be tested.

1.6.1. Plate method

See ISO 304 and NF T 73-060 (Surface active agents — determination of surface tension by drawing up liquid films).

1.6.2. Stirrup method

See ISO 304 and NF T 73-060 (Surface active agents — determination of surface tension by drawing up liquid films).

1.6.3. Ring method

See ISO 304 and NF T 73-060 (Surface active agents — determination of surface tension by drawing up liquid films).

1.6.4. OECD harmonised ring method

1.6.4.1. Apparatus

Commercially available tensiometers are adequate for this measurement. They consist of the following elements:

— mobile sample table,

— force measuring system,

— measuring body (ring),

— measurement vessel.

1.6.4.1.1. Mobile sample table

The mobile sample table is used as a support for the temperature-controlled measurement vessel holding the liquid to be tested. Together with the force measuring system, it is mounted on a stand.

1.6.4.1.2. Force measuring system

The force measuring system (see figure) is located above the sample table. The error of the force measurement shall not exceed ± 10-6 N, corresponding to an error limit of ± 0,1 mg in a mass measurement. In most cases, the measuring scale of commercially available tensiometers is calibrated in mN/m so that the surface tension can be read directly in mN/m with an accuracy of 0,1 mN/m.

1.6.4.1.3. Measuring body (ring)

The ring is usually made of a platinum-iridium wire of about 0,4 mm thickness and a mean circumference of 60 mm. The wire ring is suspended horizontally from a metal pin and a wire mounting bracket to establish the connection to the force measuring system (see figure).

(All dimensions expressed in millimetres)

1.6.4.1.4. Measurement vessel

The measurement vessel holding the test solution to be measured shall be a temperature-controlled glass vessel. It shall be designed so that during the measurement the temperature of the test solution liquid and the gas phase above its surface remains constant and that the sample cannot evaporate. Cylindrical glass vessels having an inside diameter of not less than 45 mm are acceptable.

1.6.4.2. Preparation of the apparatus

1.6.4.2.1. Cleaning

Glass vessels shall be cleaned carefully. If necessary they shall be washed with hot chromo-sulphuric acid and subsequently with syrupy phosphoric acid (83 to 98 % by weight of H3PO4), thoroughly rinsed in tap water and finally washed with double-distilled water until a neutral reaction is obtained and subsequently dried or rinsed with part of the sample liquid to be measured.

The ring shall first be rinsed thoroughly in water to remove any substances which are soluble in water, briefly immersed in chromo-sulphuric acid, washed in double-distilled water until a neutral reaction is obtained and finally heated briefly above a methanol flame.

Note:

Contamination by substances which are not dissolved or destroyed by chromo-sulphuric acid or phosphoric acid, such as silicones, shall be removed by means of a suitable organic solvent.

1.6.4.2.2. Calibration of the apparatus

The validation of the apparatus consists of verifying the zero point and adjusting it so that the indication of the instrument allows reliable determination in mN/m.

The apparatus shall be levelled, for instance by means of a spirit level on the tensiometer base, by adjusting the levelling screws in the base.

After mounting the ring on the apparatus and prior to immersion in the liquid, the tensiometer indication shall be adjusted to zero and the ring checked for parallelism to the liquid surface. For this purpose, the liquid surface can be used as a mirror.

The actual test calibration can be accomplished by means of either of two procedures:

(a) Using a mass: procedure using riders of known mass between 0,1 and 1,0 g placed on the ring. The calibration factor, Φa by which all the instrument readings must be multiplied, shall be determined according to equation (1).









where:

(mN/m)

m = mass of the rider (g)

g = gravity acceleration (981 cm s-2 at sea level)

b = mean circumference of the ring (cm)

σa = reading of the tensiometer after placing the rider on the ring (mN/m).

(b) Using water: procedure using pure water whose surface tension at, for instance, 23 oC is equal to 72,3 mN/m. This procedure is accomplished faster than the weight calibration but there is always the danger that the surface tension of the water is falsified by traces of contamination by surfactants.

The calibration factor, Φb by which all the instrument readings shall be multiplied, shall be determined in accordance with the equation (2):









where:

σo = value cited in the literature for the surface tension of water (mN/m)

σg = measured value of the surface tension of the water (mN/m) both at the same temperature.

1.6.4.3. Preparation of samples

Aqueous solutions shall be prepared of the substances to be tested, using the required concentrations in water, and shall not contain any non-dissolved substances.

The solution must be maintained at a constant temperature (± 0,5 oC). Since the surface tension of a solution in the measurement vessel alters over a period of time, several measurements shall be made at various times and a curve plotted showing surface tension as a function of time. When no further change occurs, a state of equilibrium has been reached.

Dust and gaseous contamination by other substances interfere with the measurement. The work shall therefore be carried out under a protective cover.

1.6.5. Test conditions

The measurement shall be made at approximately 20 oC and shall be controlled to within ± 0,5 oC.

1.6.6. Performance of test

The solutions to be measured shall be transferred to the carefully cleaned measurement vessel, taking care to avoid foaming, and subsequently the measurement vessel shall be placed onto the table of the test apparatus. The table-top with measurement vessel shall be raised until the ring is immersed below the surface of the solution to be measured. Subsequently, the table-top shall be lowered gradually and evenly (at a rate of approximately 0,5 cm/min) to detach the ring from the surface until the maximum force has been reached. The liquid layer attached to the ring must not separate from the ring. After completing the measurements, the ring shall be immersed below the surface again and the measurements repeated until a constant surface tension value is reached. The time from transferring the solution to the measurement vessel shall be recorded for each determination. Readings shall be taken at the maximum force required to detach the ring from the liquid surface.

2. DATA

In order to calculate the surface tension, the value read in mN/m on the apparatus shall be first multiplied by the calibration factor Φa or Φb (depending on the calibration procedure used). This will yield a value which applies only approximately and therefore requires correction.

Harkins and Jordan (4) have empirically determined correction factors for surface-tension values measured by the ring method which are dependent on ring dimensions, the density of the liquid and its surface tension.

Since it is laborious to determine the correction factor for each individual measurement from the Harkins and Jordan tables, in order to calculate the surface tension for aqueous solutions the simplified procedure of reading the corrected surface-tension values directly from the table may be used. (Interpolation shall be used for readings ranging between the tabular values.)







Table: Correction of the measured surface tension Only for aqueous solutions, ρ = 1 g/cm3 r = 9,55 mm (average ring radius) r = 0,185 mm (ring wire radius)







Experimental Value (mN/m) Corrected Value (mN/m) Weight calibration (see 1.6.4.2.2(a)) Water calibration (see 1.6.4.2.2(b)) 20 16,9 18,1 22 18,7 20,1 24 20,6 22,1 26 22,4 24,1 28 24,3 26,1 30 26,2 28,1 32 28,1 30,1 34 29,9 32,1 36 31,8 34,1 38 33,7 36,1 40 35,6 38,2 42 37,6 40,3 44 39,5 42,3 46 41,4 44,4 48 43,4 46,5 50 45,3 48,6 52 47,3 50,7 54 49,3 52,8 56 51,2 54,9 58 53,2 57,0 60 55,2 59,1 62 57,2 61,3 64 59,2 63,4 66 61,2 65,5 68 63,2 67,7 70 65,2 69,9 72 67,2 72,0 74 69,2 — 76 71,2 — 78 73,2 —

This table has been compiled on the basis of the Harkins-Jordan correction. It is similar to that in the DIN Standard (DIN 53914) for water and aqueous solutions (density ρ = 1 g/cm3 and is for a commercially available ring having the dimensions R = 9,55 mm (mean ring radius) and r = 0,185 mm (ring wire radius). The table provides corrected values for surface-tension measurements taken after calibration with weights or calibration with water.

Alternatively, without the preceding calibration, the surface tension call can be calculated according to the following formula:

where:

F = the force measured on the dynamometer at the breakpoint of the film

R = the radius of the ring

f = the correction factor (1)

3. REPORTING

3.1. TEST REPORT

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

— method used,

— type of water or solution used,

— precise specification of the substance (identity and impurities),

— measurement results: surface tension (reading) stating both the individual readings and their arithmetic mean as well as the corrected mean (taking into consideration the equipment factor and the correction table),

— concentration of the solution,

— test temperature,

— age of solution used; in particular the time between preparation and measurement of the solution,

— description of time dependence of surface tension after transferring the solution to the measurement vessel,

— 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.

3.2. INTERPRETATION OF RESULTS

Considering that distilled water has a surface tension of 72,75 mN/m at 20 oC, substances showing a surface tension lower than 60 mN/m under the conditions of this method should be regarded as being surface-active materials.

4. REFERENCES

(1) OECD, Paris, 1981, Test Guideline 115, Decision of the Council C(81) 30 final.

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

(3) Pure Appl. Chem., 1976, vol. 48, p. 511.

(4) Harkins, W.D., Jordan, H.F., J. Amer. Chem. Soc., 1930, vol. 52, p. 1751.

▼M4

A.6. WATER SOLUBILITY

INTRODUCTION

1. This Test Method is equivalent to OECD Test Guideline (TG) 105 (1995). This Test Method is a revised version of the original TG 105 which was adopted in 1981. There is no difference of substance between the current version and that from 1981. Mainly the format has been changed. The revision was based on the EU Test Method ‘Water Solubility’ (1).

INITIAL CONSIDERATIONS

2. The water solubility of a substance can be considerably affected by the presence of impurities. This Test Method addresses the determination of the solubility in water of essentially pure substances which are stable in water and not volatile. Before determining water solubility, it is useful to have some preliminary information on the test substance, like structural formula, vapour pressure, dissociation constant and hydrolysis as a function of pH.

3. Two methods, the column elution method and the flask method which cover respectively solubilities below and above 10–2 g/l are described in this Test Method. A simple preliminary test is also described. It allows the determination of approximately the appropriate amount of sample to be used in the final test, as well as the time necessary to achieve saturation.

DEFINITIONS AND UNITS

4. The water solubility of a substance is the saturation mass concentration of the substance in water at a given temperature.

5. Water solubility is expressed in mass of solute per volume of solution. The SI unit is kg/m3 but g/l may also be used.

REFERENCE CHEMICALS

6. Reference chemicals do not need to be employed when investigating a test substance.

DESCRIPTION OF THE METHODS

Test conditions

7. The test is preferably run at 20 ± 0,5 °C. The chosen temperature should be kept constant in all relevant parts of the equipment.

Preliminary test

8. In a stepwise procedure, increasing volumes of water are added at room temperature to approximately 0,1 g of the sample (solid test substances must be pulverized) in a 10 ml glass-stoppered measuring cylinder. After each addition of an amount of water, the mixture is shaken for 10 minutes and is visually checked for any undissolved parts of the sample. If, after addition of 10 ml of water, the sample or parts of it remain undissolved, the experiment is continued in a 100 ml measuring cylinder. The approximate solubility is given in Table 1 below under that volume of water in which complete dissolution of the sample occurs. When the solubility is low, a long time may be required to dissolve a test substance and at least 24 hours should be allowed. If, after 24 hours, the test substance is still not dissolved, more time (up to 96 hours) should be allowed or further dilution should be attempted to ascertain whether the column elution method or flask method should be used.







Table 1 ml of water for 0,1 g soluble 0,1 0,5 1 2 10 100 > 100 approximate solubility in g/l > 1 000 1 000 to 200 200 to 100 100 to 50 50 to 10 10 to 1 < 1

Column elution method

Principle

9. This method is based on the elution of a test substance with water from a micro-column which is charged with an inert support material, previously coated with an excess of the test substance (2). The water solubility is given by the mass concentration of the eluate when this has reached a plateau as a function of time.

Apparatus

10. The apparatus consists of a microcolumn (Figure 1), maintained at constant temperature. It is connected either to a recirculating pump (Figure 2) or to a levelling vessel (Figure 3). The microcolumn contains an inert support held in place by a small plug of glasswool which also serves to filter out particles. Possible materials which can be employed for the support are glass beads, diatomaceous earth, or other inert materials.

11. The microcolumn shown in Figure 1 is suitable for the set-up with recirculating pump. It has a head space providing for five bed volumes (discarded at the start of the experiment) and the volume of five samples (withdrawn for analysis during the experiment). Alternatively, the size can be reduced if water can be added to the system during the experiment to replace the initial five bed volumes removed with impurities. The column is connected with tubing made of an inert material to the recirculating pump, capable of delivering approximately 25 ml/h. The recirculating pump can be, for example, a peristaltic or membrane pump. Care must be taken that no contamination and/or adsorption occur with the tube material.

12. A schematic arrangement using a levelling vessel is shown in Figure 3. In this arrangement the microcolumn is fitted with a one way stopcock. The connection to the levelling vessel consists of a ground glass joint and tubing made of an inert material. The flow rate from the levelling vessel should be approximately 25 ml/h.

Figure 1

Dimensions in mm

A. Connection for ground glass joint

B. Headspace

C. Interior 5

D. Exterior 19

E. Plug of glass wool

F. Stopcock

Figure 2

A. Atmospheric equilibration

B. Flowmeter

C. Microcolumn

D. Thermostatically controlled circulating pump

E. Recirculating pump

F. Two-way valve for sampling

Figure 3

A. Levelling vessel (e.g. 2,5 litres chemical flask)

B. Column

C. Fraction accumulator

D. Thermostat

E. Teflon tubing

F. Ground glass joint

G. Water line (between thermostat and column, inner diameter approximately 8 mm)

13. Approximately 600 mg of support material is transferred to a 50 ml round-bottom flask. A suitable amount of test substance is dissolved in a volatile solvent of analytical reagent quality and an appropriate amount of this solution is added to the support material. The solvent is completely evaporated, e.g. using a rotary evaporator, as otherwise water saturation of the support will not be achieved during the elution step because of partitioning on the surface. The loaded support material is soaked for two hours in approximately 5 ml of water and the suspension is poured into the microcolumn. Alternatively, dry loaded support material may be poured into the water-filled microcolumn and two hours are allowed for equilibrating.

14. The loading of the support material may cause problems, leading to erroneous results, e.g. when the test substance is deposited as an oil. These problems should be examined and the details reported.

Procedure using a recirculating pump

15. The flow through the column is started. It is recommended that a flow rate of approximately 25 ml/h, corresponding to 10 bed volumes per hour for the column described, be used. At least the first five bed volumes are discarded to remove water soluble impurities. Following this, the pump is allowed to run until equilibrium is established, as defined by five successive samples whose concentrations do not differ by more than ± 30 % in a random fashion. These samples should be separated from each other by time intervals corresponding to the passage of at least ten bed volumes. Depending on the analytical method used, it may be preferable to establish a concentration/time curve to show that equilibrium is reached.

Procedure using a levelling vessel

16. Successive eluate fractions should be collected and analysed by the chosen method. Fractions from the middle eluate range, where the concentrations are constant within ± 30 % in at least five consecutive fractions, are used to determine the solubility.

17. Double distilled water is the preferred eluent. Deionized water with a resistivity above 10 megohms/cm and total organic carbon content below 0,01 % can also be used.

18. Under both procedures, a second run is performed at half the flow rate of the first. If the results of the two runs are in agreement, the test is satisfactory. If the measured solubility is higher with the lower flow rate, then the halving of the flow rate must continue until two successive runs give the same solubility.

19. Under both procedures, the fractions should be checked for the presence of colloidal matter by examination of the Tyndall effect. The presence of particles invalidates the test and the test should be repeated after improvement of the filtering action of the column.

20. The pH of each sample should be measured, preferably by using special indicator strips.

Flask method

Principle

21. The test substance (solids must be pulverized) is dissolved in water at a temperature somewhat above the test temperature. When saturation is achieved, the mixture is cooled and kept at the test temperature. Alternatively, and if it is assured by appropriate sampling that the saturation equilibrium is reached, the measurement can be performed directly at the test temperature. Subsequently, the mass concentration of the test substance in the aqueous solution, which must not contain any undissolved particles, is determined by a suitable analytical method (3).

Apparatus

22. The following materials are needed:

— normal laboratory glassware and instrumentation;

— a device for the agitation of solutions under controlled constant temperature;

— if required for emulsions, a centrifuge (preferably thermostated); and

— analytical equipment.

Procedure

23. The quantity of test substance necessary to saturate the desired volume of water is estimated from the preliminary test. About five times that quantity is weighed into each of three glass vessels fitted with glass stoppers (e.g. centrifuge tubes, flasks). A volume of water, chosen in function of the analytical method and solubility range, is added to each vessel. The vessels are tightly stoppered and then agitated at 30 °C. A shaking or stirring device capable of operating at constant temperature should be used, e.g. magnetic stirring in a thermostated water bath. After one day, one of the vessels is equilibrated for 24 hours at the test temperature with occasional shaking. The contents of the vessel are then centrifuged at the test temperature and the concentration of the test substance in the clear aqueous phase is determined by a suitable analytical method. The other two flasks are treated similarly after initial equilibration at 30 °C for two and three days respectively. If the concentrations measured in at least the two last vessels do not differ by more than 15 %, the test is satisfactory. If the results from vessels 1, 2 and 3 show a tendency of increasing values, the whole test should be repeated using longer equilibration times.

24. The test can also be performed without pre-incubation at 30 °C. In order to estimate the rate of establishment of the saturation equilibrium, samples are taken until the stirring time no longer influences the concentrations measured.

25. The pH of each sample should be measured, preferably by using special indicator strips.

Analytical determinations

26. A substance-specific method is preferred since small amounts of soluble impurities can cause large errors in the measured solubility. Examples of such methods are: gas or liquid chromatography, titration, photometry, voltametry.

DATA AND REPORTING

Data

Column elution method

27. For each r