ASTM D5769 for Benzene, Toluene and Total Aromatics in Finished Gasolines
ASTM D5769 Standard Test Method for Determination of Benzene, Toluene, and Total Aromatics in Finished Gasolines by Gas Chromatography/Mass Spectrometry
10. Quality Control Reference Material
10.1 After the calibration has been completed, prepare the quality control reference material outlined in Table 6. Analyze the reference material as described in Sections 11-13. The individual aromatic and total aromatics values obtained shall agree within more or less 5 % relative of the values in the prepared reference material (for example, benzene 1.0 more or less 0.05) except for 1,2,4,5-tetramethylbenzene and naphthalene, which must be within more or less 10 % relative of the values specified. If the individual values are outside the specified range, verify calibration and instrumental parameters, including linearity of injection port splitter (both in concentration and boiling point) for calibration solutions, linearity of mass spectrometer response, purity of reagents, stability or repeatability of GC/MS system, accuracy of the preparation of quality control reference material, and so forth. DO NOT analyze samples without meeting the quality control specifications.
10.2 If samples containing oxygenated fuel additives, such as ethanol or methyl-t-butyl ether (MTBE), are to be analyzed in addition to conventional oxygenates-free gasolines, then it is recommended that several quality control reference materials be prepared containing the major oxygenated additives at levels found in gasolines to demonstrate that the injection/chromatographic performance is independent of sample types.
10.3 If the linear least squares calibration does not yield results that meet the more or less 5 % specification for the reference material above, then try forcing the calibration through the origin, that is, bi = 0, using the GC/MS quantitation software and recalculate the results for the reference material. For components present in high concentrations, such as toluene, try using a quadratic fit as described in 9.3.6. If the results for the reference material are still in error, verify the calibration and instrument set-up.
10.4 Analyze the quality control reference materials before every batch of samples. It is recommended that the samples are bracketed by the reference materials specified in 10.1. If the reference material does not meet the specifications in 10.1, the samples analyzed immediately preceding the reference material are considered suspect and should be rerun. Returning of the mass spectrometer and drift with time may require recalibration of the GC/MS system. See Section 9.
10.5 In addition to the analysis of the QC sample in Table 6, it is strongly recommended that a gasoline reference material be analyzed routinely as part of the QC program. Such gasoline reference materials are available from commercial vendors.
