Mass fraction of impurities in a technical chlorpyrifos sample may be obtained by selective determination on carbon (496 nm and 193 nm), chlorine(479 nm), and sulfur (181 nm) channels using gas chromatography with atomic emission detection(GC/AED). According to the formulas from GC/MS and analytical results from GC/AED, mass fraction of compounds may be calculated by internal standard of elements. The results for the same compound obtained from different elemental channels were consistent. This shows the responses of carbon, chlorine and sulfur on AED are independent on molecular structures. Moreover, the reliability of the qualitative results of impurities from GC/MS was proved. If the formulas from GC/MS were wrong, the results from different elemental channels on GC/AED would be different. The relative deviations were in the range of -3.4% to 5.8%. When standards are not available, the results from GC/AED are more reliable than those from GC/FID which usually depend on the area normalization without corrections. Pesticides and other complex organic mixtures may be analyzed reliably and expediently by this method.