ASTM D5917 Test Method for Trace Impurities in Monocyclic Aromatic Hydrocarbons
ASTM D5917 Standard Test Method for Trace Impurities in Monocyclic Aromatic Hydrocarbons by Gas Chromatography and External Calibration
4. Summary of Test Method
4.1 A repeatable volume of the specimen to be analyzed is precisely injected into a gas chromatograph equipped with a flame ionization detector (FID). The peak area of each impurity is measured. Concentration of each impurity is determined from the linear calibration curve of peak area versus concentration. Purity by gas chromatography (GC) is calculated by subtracting the sum of the impurities found from 100.00. Results are reported in weight percent.
5. Significance and Use
5.1 Determining the type and amount of hydrocarbon impurities remaining from the manufacture of toluene, mixed xylenes, and p-xylenes used as chemical intermediates and solvents is often required. This test method is suitable for setting specifications and for use as an internal quality control tool where these products are produced or are used. Typical impurities are: alkanes containing 1 to 10 carbons atoms, benzene, toluene, ethylbenzene (EB), xylenes, and aromatic hydrocarbons containing nine carbon atoms.
5.1.1 Refer to Test Method D2306 for determining the C8 aromatic hydrocarbon distribution in mixed xylenes.
5.2 Purity is commonly reported by subtracting the determined expected impurities from 100.00. However, a gas chromatographic analysis cannot determine absolute purity if unknown or undetected components are contained within the material being examined.
5.3 This test method is similar to Test Method D2360, however, interlaboratory testing has indicated a bias may exist between the two methods. Therefore the user is cautioned that the two methods may not give comparable results.
6. Interferences
6.1 In some cases for mixed xylenes and p-xylene, it may be difficult to resolve benzene from the nonaromatic hydrocarbons. Therefore the concentrations are determined as a composite. In the event that the benzene concentration must be determined, an alternate method such as Test Method D6526 must be selected to ensure an accurate assessment of the benzene concentration.
6.2 Complete separation of ethylbenzene and m-xylene from p-xylene is difficult and can be considered adequate if the distance from baseline to valley between peaks is not greater than 50 % of the peak height of the impurity.
