Microanalysis of explosives and propellants by on‐line supercritical fluid extraction/chromatography with triple detection

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Abstract
A compact analytical instrument is described which allows microsamples to be extracted with supercritical fluids, and the extract preconcentrated and analyzed by capillary supercritical fluid chromatography in a single coupled unit. Thus, no off‐line sample pretreatment is required, and the possibility of extraneous contamination is reduced. To achieve greater selectivity and sensitivity for selected species, three different detectors (UV absorption, flame ionization and electron capture) were all connected on‐line. This analytical instrument configuration was established by upgrading a commercial capillary supercritical fluid chromatograph using regular chromatographic supplies. To illustrate the analytical utility of this hyphenated technique, an assortment of compounds that are not easily determined by traditional gas chromatographic or liquid chromatographic methods was selected: explosives, propellants, and related species. The instrumental design, as well as selected analytical conditions (sample pretreatment, extraction, preconcentration, separation, and detection) were investigated to improve selectivity and/or sensitivity. The determination of explosive residues on soil is described as an environmental analysis application of the system. Detection limits for some compounds are estimated to be as low as 100 pg. The firearm propellants were characterized through their extractable organic constituents, and the usefulness of such characterization in forensic investigations is discussed. Closely related to this issue is the analysis of the residue in expended cartridge cases. A chromatographic fingerprint was obtained from the propellant used in the ammunition. This fingerprint can be used under certain circumstances to correlate a specific batch of propellant with the residue left in a fired cartridge case.