ASTM D2503-92(1997)
(Test Method)Standard Test Method for Relative Molecular Mass (Molecular Weight) of Hydrocarbons by Thermoelectric Measurement of Vapor Pressure
Standard Test Method for Relative Molecular Mass (Molecular Weight) of Hydrocarbons by Thermoelectric Measurement of Vapor Pressure
SCOPE
1.1 This test method covers the determination of the average relative molecular mass (molecular weight) of hydrocarbon oils. It can be applied to petroleum fractions with molecular weights (relative molecular mass) up to 3000; however, the precision of the method has not been established above 800 molecular weight (relative molecular mass). The method should not be applied to oils having initial boiling points lower than 220°C.
1.2 Values stated in SI units are to be regarded as the standard. The values given in parentheses are provided for information purposes only.
1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.> For specific hazard statements, 5.2.1, 5.2.3, and 5.2.3.
General Information
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Standards Content (Sample)
Designation: D 2503 – 92 (Reapproved 1997) An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Relative Molecular Mass (Molecular Weight) of
Hydrocarbons by Thermoelectric Measurement of Vapor
1
Pressure
This standard is issued under the fixed designation D 2503; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3.2 A knowledge of the relative molecular mass (molecular
weight ) is required for the application of a number of
1.1 This test method covers the determination of the average
correlative methods that are useful in determining the gross
relative molecular mass (molecular weight) of hydrocarbon
composition of the heavier fractions of petroleum.
oils. It can be applied to petroleum fractions with molecular
weights (relative molecular mass) up to 3000; however, the
4. Apparatus
precision of the method has not been established above 800
2
4.1 Vapor Pressure Osmometer, with operating diagram.
molecular weight (relative molecular mass). The method
should not be applied to oils having initial boiling points lower
5. Reagents and Materials
than 220°C.
1.2 Values stated in SI units are to be regarded as the 5.1 Purity of Reagents—Reagent grade chemicals shall be
standard. The values given in parentheses are provided for used in all tests. Unless otherwise indicated, it is intended that
information purposes only. all reagents shall conform to the specifications of the Commit-
1.3 This standard does not purport to address all of the tee on Analytical Reagents of the American Chemical Society,
3
safety concerns, if any, associated with its use. It is the where such specifications are available. Other grades may be
responsibility of the user of this standard to establish appro- used, provided it is first ascertained that the reagent is of
priate safety and health practices and determine the applica- sufficiently high purity to permit its use without lessening the
bility of regulatory limitations prior to use. For specific hazard accuracy of the determination.
statements, 5.2.1, 5.2.3, and 5.2.3. 5.2 Solvents—Solvents that do not react with the sample
must be used. Since many organic materials exhibit a tendency
2. Summary of Test Method
to associate or dissociate in solution, it is desirable to use polar
2.1 A weighed portion of the sample is dissolved in a known
solvents for polar samples and nonpolar solvents for nonpolar
quantity of appropriate solvent. A drop of this solution and a samples. The solvents listed have been found suitable for
drop of solvent are suspended, side by side, on separate
hydrocarbons and petroleum fractions.
thermistors in a closed chamber saturated with solvent vapor. 5.2.1 Benzene
Since the vapor pressure of the solution is lower than that of the
NOTE 1—Warning: Poison. Carcinogen. Harmful if swallowed. Ex-
solvent, solvent condenses on the sample drop and causes a
tremely flammable. Vapors may cause flash fire. Vapor harmful, may be
temperature difference between the two drops. The resultant
absorbed through skin.
change in temperature is measured and used to determine the
5.2.2 Chloroform
relative molecular mass (molecular weight) of the sample by
reference to a previously prepared calibration curve.
NOTE 2—Warning: May be fatal if swallowed. Harmful if inhaled.
May produce toxic vapors if burned.
3. Significance and Use
5.2.3 1,1,1-Trichloroethane
3.1 Relative molecular mass (molecular weight) is a funda-
mental physical constant that can be used in conjunction with
other physical properties to characterize pure hydrocarbons and
2
A vapor pressure osmometer is available from H. Knauer and Co., Berlin, West
their mixtures.
Germany. The manufacture of the Mechrolab instrument previously referred to in
this footnote has been discontinued. However, some models may be available from
stocks on hand at laboratory supply houses, or as used equipment from laboratory
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This test method is under the jurisdiction of ASTM Committee D-2 on instrument exchanges.
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Petroleum Products and Lubricantsand is the direct responsibility of Subcommittee “Reagent Chemicals, American Chemical Society Specifications,” Am. Chemi-
D02.04on Hydrocarbon Analysis. cal Soc., Washington, DC. For suggestions on the testing of reagents not listed by
Current edition approved Aug. 15, 1992. Published October 1992. Originally the American Chemical Society, see “Analar Standards for Laboratory U.K.
e1
published as D 2503 – 66T. Last previous edition D 2503 – 82 (1987) . Chemicals,” BDH Ltd., Poole, Dorset, and the “United States Pharm
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