VOCs analytical methods columns

Column selection is based on the compoimd list, detector used, and analytical method. For specific usage of different columns used for VOCs separations the reader is directed to the application table in each extraction section. Standardized analytical methods suggest the chromatographic column to use. 

Thermal Desorption Thermal desorption is an alternative GC inlet system particularly used for VOC analysis. However, the analytes subjected to thermal desorption must be thermally stable to achieve successful analysis. Otherwise, decomposition occurs. This technique is mainly used for determination of volatiles in the air. Such a methodology requires sample collection onto sohd sorbents, then desorption of analytes and GC analysis. Traditionally, activated charcoal was used as a sorbent followed by extraction with carbon disulfide. However, solvent desorption involves re-dilution of the VOCs, thus partially negating the enrichment effect. Therefore, the sampling method is to pump a sample of gas (air) through the sorbent tube containing certain sorbents in order to concentrate the VOC. Afterwards, the sample tube is placed in thermal desorber oven and the analytes are released from the sorbent by application of high temperature and a flow of carrier gas. Additionally, desorbed compounds are refocused in a cold trap and then released into the GC column. Such a two-step thermal desorption process provides a narrow chromatographic band at the head of the column. 

Acceptable forensic practice recommends confirmation of the detection of an analyte (drug) by a second or definitive method. For VOCs, two acceptable GC confirmation procedures are re-sampling and re-analysis using a different column or use of mass spectrometry for absolute identification. 

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