6: What Is Qualitative Analysis and How Do I Perform It?

Qualitative data analysis is the “what” is present in my sample, whilst quantitative analysis is the “how much”. In qualitative analysis GC is used to confirm the presence or absence of analytes in a sample whose identities are known. GC may not lead to the positive identification of an analyte, but provides evidence of absence of a species or if it is present below the detection limit of the method. Failure of a sample to produce a peak at the same retention time as the standard obtained under identical conditions is strong evidence of absence. GC-MS provides additional information that can be used in this process for confirmation with the mass spectrum of the analyte. The identification of unknown analytes in a sample needs particular detectors such as mass-selective detection (MSD), ultraviolet (UV) and infrared (IR). Other data mining operations are also performed under the ‘qualitative analysis’ header, for example system suitability calculations to check that the instrument is performing as it should be and integration which is needed for quantitative analysis.