# 102 Adopted: 27.07.95



## O E C D G UI D E L I N E F O R T H E T E ST I N G O F C H E M I C A L S
Adopted by the Council on 27 th 

### July 1995 M el t i n g P oi n t / M el t i n g R a n ge

I N T RO DUC T I O N 1. This guideline is a revised version of the original Guideline 102 which was adopted in 1981. Mainly the format has been changed. The differences of substance between this version and that from 1981 are few. The meniscus method, which is applicable to polyam ides, has not been retained and the pour point is included. The revision was based on the EC method "Melting/Freezing Temperature" published in 1992 (1).

I N I T I

A L C O NSI D E RA T I O NS 2. Frequen tly the transition from s olid to liquid phase takes place over a temperature range. Therefore, the term "melting range" is often used and, in practice, the temperatures of the initial and final stages of melting are determined. The melting point ideally is iden tical with the s olidification or freezing point. For some substances (rather products and mixtures) however, the determination of the freezing or solidification tem perature is easier. Where, due to the particular properties of the substance (or product), none of the above parameters can be convenien tly meas ured, a pour point may be appropriate.
3. The fundamental prin ciples are g iven in references 2 and 3. Several methods and devices are described in this g uideline. They can be applied irrespective of the degree of purity of the substance. The melting point of a substance is cons iderably affected by impurities. For this reason it serves as a measure of a substance's purity. The selection of a particular method depends mainly on the state of physical aggreg ation of the sam ple and on whether or not the substance can be pulverized easily, with difficulty, or not at all. Stan dards des cribing the various devices and procedures are listed in the Appendix.

D E F I

N I T I O NS A N D UNI T S 4. The melting point is defined as the temperature at which the phase trans ition from the s olid to the liquid state at atmospheric pressure takes place.
5. The conversion of kelvins to deg rees Celsius is according to the formula T = t + 273.15 , where T is the Kelvin or thermodynamic tem perature and t the Celsius tem perature.

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# 102 OCD E/OECD
RE F E RE N C E SUBST A N C E S 6. Reference substances do not n eed to be employed when investig ating a substance. Some calibration substances are listed in reference 4.

P RI N C I P L E O F T H E T E S T 7. The temperature or temperature range of the phase trans ition from the s olid to the liquid state or from the liquid to the solid state is determined.

C O M P A RI SO N O F T H E M E T H O DS 8. The temperature range and accuracy of the different methods are listed in Table 1.

Table 1

Method Temperature range (in K) Esti mated accuracy (in K) Capillary/liquid bath 273 to 573 ± 0.3 Capill ary/metal block 293 to >573 ± 0.5 Kofler hot bar 293 to >573 ± 1.0 Melt microscope 293 to >573 ± 0.5 Differential thermal analysis and differential scanning calorimetry 173 to 1273 ± 0.5 up to 600 K ± 2.0 up to 1273 K Freezing temperature 223 to 573 ± 0.5 Pour point 223 to 323 ± 3.0

D E SC RI P T I O N O F T H E M E T H O DS
C a p illa r y t u b e in a liq u id b a t h Apparatus 9. The apparatus m ade of glass is shown in Figure 1. The choice of the bath liquid depends upon the melting tem perature to be determin ed, e.g. liquid paraffin for tem peratures not higher than 473 K and s ilicone oil for temperatures not higher than 573 K. For temperatures above 523 K, a mixture of three parts sulfuric acid and two parts of potassium s ulph ate (weight ratio) can be used. Precautions should be taken if a mixture such as this is used. Only thermom eters, fulfilling the requirements of the stan dards ASTM E 1-71, DIN 12770, and JIS K 8001, or equivalent, should be used. The middle part of the mercury bulb of the thermometer should touch the capillary at the position wh ere the sample is located.

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# 102
Figure 1

Dimensions in mm
A. Vessel B. Stopper C. Vent D. Thermometer E. Auxiliary thermometer F. Bath liquid G. Sample tube; max 5 mm outer diameter; capillary tube, approx 100 mm long and approx 1 mm inner diam eter, and approx 0.2 to 0.3 mm wall-thickness H. Side tube

Figure 2

Stage A, beginning of melting, fine dropl ets adhere uni formly to the wall of the tube Stage B, a cl earance between the sample and the wall due to shrinkage of the melt Stage C, the shrunken sample coll apses and li quefies Stage D, a compl ete meni scus is formed but part of the sample remains solid Stage E, final stage of melting, no solid particles are left
Procedure 10. The dry substance is finely pulverized and put into a capillary tube, fused at one end, so that the filling level is approxim ately 3 mm after the sample has been tigh tly packed. To obtain a uniformly packed sample, the capillary tube should be dropped from a height of approxim ately 700 mm through a glass tube onto a w atch glass. The bath is h eated so that the temperature rise is approxim ately 3 K/min. The bath sh ould be stirred. Usually the capillary tube is put into the

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# 102 OCD E/OECD apparatus when the temperature has risen to about 10 K below the melting tem perature. From then on, and through out the actual m elting, the tem perature rise is adjusted to maximum 1K/min. When subjected to a slow temperature rise, finely pulverized substances us ually show the stages of m elting shown in Figure 2. During the determination of the m elting tem perature, the temperatures are recorded at the beginning of the melting (stage A in the fig ure) and at the final stage (stage E in the figure).
Calculations 11. A corrected m elting tem perature is calculated using the formula
T = T D + 0.00016 (T D - T E ) n , where
T = corrected m elting temperature, T D = reading of thermom eter D, T E = reading of thermom eter E, n = number of g raduations of the mercury column on the emergent stem of thermometer D.
C a p illa r y t u b e in a m et a l b lock Apparatus for visual observation Figure 3

A. Thermometer B. Capillary tube C. Eye-piece D. Electrical resistance E. Metal heating block F. Lamp G. Metal plug

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12. The apparatus shown in Figure 3 consists of: - a cylin drical metal block, the upper part of which is h ollow and forms a chamber; - a metal plug, with two or m ore holes, allowing capillary tubes to be mounted in the block; - an electrical h eating system with reg ulated power in put; - four windows of h eat-resistant glass on the lateral walls of the cham ber, diametrically disposed at right angles; - an eyepiece for obs erving the capillary tube, mounted in front of one of these windows (the other three windows are used for illuminating the ins ide of the enclos ure); - a thermometer according to standards men tioned in paragraph 9 or therm oelectrical meas uring devices of comparable accuracy. Apparatus with photocell detection 13. A capillary tube, filled as described in paragraph 10, is placed in a heated metal block. The temperature rise is adjusted at a suitable pre-selected linear rate. A beam of light is directed th rough the sample to a photocell. On m elting of the sam ple, the intensity of the light reaching the photocell increases and a stop signal is sent to the digital indicator reading out the temperature of the h eating chamber.
K ofler h ot b a r Apparatus 14. The Kofler hot bar uses two pieces of metal of different thermal con ductivity. The bar is heated electrically and is designed so that the temperature g radient is almost lin ear along its length. The temperature of the hot bar can range approxim ately from room tem perature to 573 K. The bar is fitted with a graduated temperature s cala and a movable poin ter.
Procedure 15. The substance is laid in a thin layer on the hot bar. A sharp dividing line develops between the solid and fluid phase within a few seconds. The temperature at the dividing line is read by adjusting the poin ter to the dividing line.
M elt m icr os cop e 16. The specimen h older of a m elt micros cope is a metal plate which is part of a h eating cham ber. A hole in the metal plate permits the entrance of light from an illumin ating device. The sample is placed on a slide over the hole and may be covered by another slide to minimise exposure to air. The plate is heated gradually until m elting is obs erved and the temperature is recorded. The accuracy of the measurement can be in creased for crys talline substances through the use of polarised light.
Differ en t ia

l t

h er m a l a n a ly s is (DT A ) 17. Samples of the test substance and of a reference m aterial are subjected to the same con trolled temperature programme. When the test substance undergoes a phase transition, the corresponding change of enthalpy gives an en dothermic (melting) or exothermic (freezing) departure from the base line of the temperature record.
Differ en t ia

l s ca n n in g ca lor im et

r y (DSC ) 18. Samples of the test substance and of a reference m aterial are subjected to the same con trolled temperature programme. The difference in energy input n ecess ary to main tain iden tical temperatures between the substance and the reference m aterial is recorded. When the sample un dergoes a phase

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# 102 OCD E/OECD transition, the corresponding change of enthalpy gives a departure form the base line of the h eat flow record.
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e 19. A sample of the substance is placed in a test tube and stirred continuously. As the sample is cooled, its temperature is measured at regular intervals. As soon as the temperature remains constant for a few readings (corrected for thermom eter error), this temperature is recorded as the freezing temperature. Supercooling must be avoided by main taining equilibrium between the s olid and the liquid phases.
P ou r p oin t 20. This method was developed for petroleum oils and is suitable for oily substances with low melting tem peratures. After prelimin ary h eating, the sam ple is cooled and its flow ch aracteristics are examined at intervals of 3 K. The lowest temperature at which m ovement of the substance is obs erved is recorded as the pour point.

T E S T RE P O RT 21. The test report shall include the following in form ation: - method used; - chemical iden tity and impurities (prelimin ary purification step, if any); - estimated accuracy; - melting tem perature (the mean of at least two meas urements which are in the range of the estimated accuracy; if the difference between the temperature at the beginning and at the final stage of melting is within the limits of the accuracy, the temperature at the final stage of melting is taken as the m elting temperature; otherwise the two tem peratures are reported; if the substance decomposes or sublimes before m elting occurs, the temperature at which the effect is observed is reported); - all in form ation and rem arks relevant for the interpretation of the results, especially with regards to impurities and physical state of the substance.

L I T E RA T URE
(1) Official J ournal of the European Commun ities L 383 A, 5-14 (1992) (2) Le Nein dre, B. and Vodar B., eds. (1975). IUPAC, Ex perimen tal Therm odynamics, Vol.II, Butterw orths, London, pp. 803 to 834 (3) Weissberg er, R., ed. (1959). Technique of Organic Chemis try, Vol. I, Part I, Chapter VII, Physical Methods of Organic Chemis try, 3rd ed., Inters cience Publ., New York. (4) IUPAC (1976). Physicochem ical meas urements: Catalogue of reference materials from n ational laboratories, Pure and Applied Chemistry, 48 , 505 to 515

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A P P E NDI X
L I S T O F S T A NDA RDS

C a p illa r y t u b e in a liq u id b a t h ASTM E 324-69 Stan dard test method for relative initial and final m elting points and the melting range of organic chem icals
BS 4634 Method for the determination of m elting point an d/or m elting range DIN 53181 Bindemittel für L acke und ähn liche Beschichtungsstoffe;Bestimmung des Schmelzbereiches von Harzen nach KapillarVerfahren JIS K 00-64 Testing methods for m elting point of chem ical products
C a p illa r y t u b e in a m et a l b lock DIN 53736 Visuelle Bestimmung der Schmelztemperatur von teilkristallinen Kunsts toffen
K ofler h ot b a r ANSI / ASTM D 3451-76 Stan dard recommen ded practices for testing polym eric powders and powder coatings
M elt m icr os cop e DIN 53736 Visuelle Bestimmung der Schmelztemperatur von teilkristallinen Kunsts toffen

Differ en t ia

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h er m a l a n a ly s is a n d d iffer en t ia

l s ca n n in g ca lor im et

r y ASTM E 472-86 Stan dard practice for reporting thermoan alytical data
ASTM E 473-85 Stan dard definitions of terms relating to thermal an alysis
ASTM E 537-76 Stan dard method for assessing the thermal stability of chemicals by methods of differen tial thermal analysis DIN 51005 Thermische Analyse (TA)

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e BS 4633 Method for the determination of crys tallizing point
BS 4695 Method for the determination of m elting point of petroleum wax (cooling curve)

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# 102 OCD E/OECD DIN 51421 Bestimmung des Gefrierpun ktes von Flug krafts toffen, Ottokrafts toffen und Motorenbenzolen DIN 53175 Bestimmung des Ers tarrungspun ktes von Fetts äuren ISO 1392 Method for the determination of the crys tallizing point ISO 2207 Petroleum waxes - Determination of congealing point JIS K 00 - 65 Test methods for freezing point of chem ical products
NF T 60-114 Point de fusion des paraffines
NF T 20-051 Méth ode de détermination du point de cristallis ation

P ou r p oin t ASTM D 97-66 Stan dard test method for pour point of petroleum oils
ISO 3016 Petroleum oils - Determination of pour point
NBN 52014 Echan tillonnage et an alyse des produits de pétrole: Point de trouble et point d'écoulement limite

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EPA-HQ-OPPT-2007-0531-DRAFT-1203 Guideline for the Testing of Chemicals:Melting Point/Melting Range, OECD 102, July 27,1995 09/28/2010

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