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Rapid Semi-Quantitative Surface Mapping of Airborne-Dispersed Chemicals Using Mass Spectrometry
Citation:
GRANGE, A. H. Rapid Semi-Quantitative Surface Mapping of Airborne-Dispersed Chemicals Using Mass Spectrometry. Environmental Forensics Journal 10(3):183-195, (2009).
Impact/Purpose:
Mapping a contaminated site semi-quantitatively into high, moderate, low, and non-detect levels would aid in assessing risks posed by the site to humans and the environment and document thorough clean-ups. Four requirements must be met to provide rapid analyses for delineating semi-quantitatively with high spacial resolution the distribution of chemicals resulting from deliberate, accidental, or weather-related dispersion of chemicals. Samples from numerous locations must require little or no sample preparation prior to analysis, must be analyzed in seconds, must be analyzed sequentially after a short intra-sample time, and software to rapidly plot semi-quantitation maps must be written. An inexpensive autosampler that provides mass spectral analyses of 76 cotton swab, wipe samples in 7.5 min was built previously (Grange, 2008a, 2008b) to provide rapid analysis with a short intra-sample time. The cotton swab wipe samples were pulled through the flow of hot, energized helium from a DARTTM ion source. Operation of the DARTTM is simple relative to ambient-air sources that require adjustment of numerous variables and continuous delivery of solutions to the ionization region during analyses (Takáts, 2005). To limit sample preparation, a field sample carrier was built to simplify wipe sample collection and label bookkeeping and to provide the swabs to the laboratory nearly ready for analysis (Grange, 2008c). The macro procedures required to rapidly plot multi-color, semi-quantitation maps based on individual ion chromatograms obtained for sets of swabs is briefly described herein.
Description:
Chemicals can be dispersed accidentally, deliberately, or by weather-related events. Rapid mapping of contaminant distributions is necessary to assess exposure risks and to plan remediation, when needed. Ten pulverized aspirin or NoDozTM tablets containing caffeine were dispersed across a concrete driveway using the exhaust port of a shop vacuum cleaner. Water-soaked, cotton swabs were used to collect wipe samples from 100 cm2 areas within a 7 x 12 grid pattern to map the caffeine distribution. An autosampler/Direct Analysis in Real Time (DARTTM)/ time-of-flight mass spectrometer was used to acquire ion chromatograms for the [M+H]+ semi-quantitation ion (m/z 195). Prior to analysis, unheated, non-energized helium gas was blown across the swabs to remove debris that could plug the cone orifice. Carry over was mitigated by interspersing wipe sample swabs with water-soaked swabs to provide hot water vapor to clean the region around the cone orifice into the mass spectrometer between sample swabs. Carry over was further reduced relative to the ion abundances from analyte peaks by acquiring data a second time. Remaining carry over was seen as ion abundance plateaus in ion chromatograms before and after each analyte peak. The higher plateau was treated as the baseline for each analyte peak by a macro procedure written in Lotus 123TM. A second macro procedure plotted multi-color, semi-quantitation maps for high, moderate, low, and non-detect levels of caffine.
URLs/Downloads:
GRANGE FIGURES FOR FINAL JOURNAL.PDF (PDF, NA pp, 166 KB, about PDF)GRANGE 08-165 FINAL JOURNAL 1..PDF (PDF, NA pp, 73 KB, about PDF)