Halogen, detection estimation

The material evaporated by the laser pulse is representative of the composition of the solid, however the ion signals that are actually measured by the mass spectrometer must be interpreted in the light of different ionization efficiencies. A comprehensive model for ion formation from solids under typical LIMS conditions does not exist, but we are able to estimate that under high laser irradiance conditions (>10 W/cm ) the detection limits vary from approximately 1 ppm atomic for easily ionized elements (such as the alkalis, in positive-ion spectroscopy, or the halogens, in negative-ion spectroscopy) to 100—200 ppm atomic for elements with poor ion yields (for example, Zn or As). 

Hagenmaier et al. [59] have described a method for the quantitative gas chromatographic determination of volatile halogenated hydrocarbons in lake water samples. Sample enrichment is effected by liquid-liquid extraction with pentane, followed by separation on a capillary gas-liquid chromatographic column, with electron capture detection. A 1 25 pentane-water ratio was employed in conjunction with a standard solution of a reference compound (1-bromobutane) for estimating extraction... 

Analysis by TLC. Confirmation of the identity of the halogenated compounds in the soil samples was achieved by resolution of selected extracts on TLC plates, followed by gas chromatography of the separate compounds eluted from the plates. The thin layer chromatography system of Kovacs (6) was used, and the halogenated compounds were detected with the silver nitrate-2-phenoxyethanol reagent. Comparison with standards chromatographed on the same plates permitted an estimate of the pesticide concentrations. 

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