ASTM D2503 Standard Test Method for Relative Molecular Mass (Molecular Weight) of Hydrocarbons by Thermoelectric Measurement of Vapor Pressure
4. Apparatus
4.1 Vapor Pressure Osmometer, with operating diagram.
5. Reagents and Materials
5.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
5.2 Solvents - Solvents that do not react with the sample must be used. Since many organic materials exhibit a tendency to associate or dissociate in solution, it is desirable to use polar solvents for polar samples and nonpolar solvents for nonpolar samples. The solvents listed have been found suitable for hydrocarbons and petroleum fractions.
5.2.1 Benzene (Warning - Poison. Carcinogen. Harmful if swallowed. Extremely flammable. Vapors may cause flash fire. Vapor harmful, may be absorbed through skin.)
5.2.2 Chloroform (Warning - May be fatal if swallowed. Harmful if inhaled. May produce toxic vapors if burned.)
5.2.3 1,1,1-Trichloroethane (Warning - Harmful if inhaled. High concentrations may cause unconsciousness or death. Contact may cause skin irritation and dermatitis.)
NOTE 1 - The precision data given in 10.1 will apply only when benzene is used as the solvent. There is also some evidence that determinations on the same oil sample carried out in different solvents will produce results that differ somewhat in absolute magnitude of apparent molecular weight (relative molecular mass).
5.3 Reference Standards - A calibration curve must be constructed for each new lot of solvent using a pure compound whose relative molecular mass (molecular weight) is accurately known. Compounds that have been used successfully include benzil (210.2), n-octadecane (254.5), and squalane (422.8).
