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
13. Procedure
13.1 Bring the sample and calibration mixtures to identical temperatures, preferably 25°C. Make sure that the temperature of the sample is consistent with that of the calibration standard prepared in Section 12.
13.2 Depending upon the actual chromatograph's operating conditions, inject an appropriate amount of sample into the instrument. The injection amount shall be identical to the amount used in 12.3 and must be consistent with those conditions used to meet the criteria in 12.7.
13.3 Measure the area of all peaks except the major component(s). Measurements on the sample must be consistent with those made on the calibration blend. The nonaromatic fraction includes all peaks up to toluene (except for the peak assigned as benzene). Sum together all the nonaromatic peaks and report as a total area. The C9 aromatics fraction includes cumene and all peaks emerging after o-xylene, with exception of PDEB. Sum together all the C9 aromatic peaks and report as a total area. If PDEB is included in the calibration, report PDEB.
13.4 A poorly resolved peak, such as m-xylene, will often require a tangent skim from the neighboring peak. Make consistent measurements on the specimen and calibration chromatograms for tangents or poorly resolved peaks.
13.5 Fig. 2 illustrates the analysis of Specification D841, Toluene. Fig. 3 illustrates the analysis of Specification D5211, Mixed Xylene. Fig. 4 illustrates the analysis of Specification D5136, p-xylene.
14. Calculations
14.1 Calculate the weight percent concentration of the total nonaromatics and each impurity as follows. Use the response factor determined for n-nonane for all nonaromatic components, the factor for o-xylene for o-xylene, the factor for m-xylene for m-xylene, the factor for cumene for all aromatic hydrocarbons containing nine or more carbon atoms with exception of PDEB, and if PDEB is included in the calibration, the PDEB factor for PDEB as follows:
Ci = AiRFiDc/Ds
where:
Ci = concentration of impurity i, weight %,
Ai = peak area of impurity i,
RFi = response factor of impurity i, from 12.4,
Dc = density of calibration solution (p-xylene), from Table 2, and
Ds = density of sample, from Table 2 or Test Method D4052.
14.2 Calculate the weight percent purity of the sample as follows:
purity, weight % = 100.00 - Ct
where: Ct = total concentration of all impurities, weight %.
14.3 Calculate the total mixed xylenes by summing the concentration of o-xylene, p-xylene, m-xylene and ethylbenzene.
