In many instances, the analysis of the vapor above a sample (that is, the headspace) is the best means of assessing the presence of an analyte or even its concentration in a condensed phase. This is especially true for forensic samples or artifacts. The traditional methods of headspace sampling include static and dynamic purge and trap, and the modern SPME techniques work well for many matrices; all have advantages and disadvantages. The new method of PLOT-cryoadsorption is a dynamic sampling method that utilizes short porous layer capillaries at reduced temperature as the sorbent. This method is very sensitive and quantitative, and can be used over a wide temperature range. Because the method is dynamic, the composition profile of the vapor is not time dependent, the vapor collections are very rapid, and analysis can be done with nearly all instrumental methods. Published applications of this technique in the laboratory include vapor sampling for explosives, adulterated food, decomposing corpses, and arson fire debris. Vapor sampling done with PLOT-cryo is quantitative, and the uncertainty low enough such that the results can be interpreted with the van’t Hoff equation. While the concentration limits vary with analyte and instrumental technique chosen, analytes present at the ppb level can be readily detected. Moreover, PLOT-cryo can be directly interfaced with pyrolysis, greatly expanding the applicability. In the field, a portable PLOT-cryo has been used to measure fuel spills on soil. This talk will be an overview of the method, covering the basic technology and the major variations and features. Applications will be drawn from the examples mentioned above. We will focus not only on the use of PLOT-cryo in the laboratory but also a field portable device that can operate in remote locations.

Vapor sampling by PLOT-cryoadsorption: Examples in forensic sample analysis

249th National Meeting (2015)

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