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Rapid Semi-Quantitative Mapping of Dispersed Caffeine Using an Autosampler/DART/TOFMS
Citation:
GRANGE, A. H. Rapid Semi-Quantitative Mapping of Dispersed Caffeine Using an Autosampler/DART/TOFMS. Presented at American Society for Mass Spectrometry, Philadelphia, PA, May 31 - June 04, 2009.
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Presentation
Description:
Introduction: Rapid mapping of contaminant distributions is necessary to assess exposure risksand to plan remediation, when chemicals are dispersed accidentally, deliberately, or by weather-related events. Described previously (Grange, Environ. Forensics, 9, 125-141) were anautosampler for a DART/TOFMS based on N-scale model railroad components that samples 76cotton swab, wipe samples in 7.5 min and a field sample carrier for the swabs built around theautosampler's support element for the swabs. To test the ability to semi-quantitatively mapdispersion of a chemical, pulverized Nodoz (45% caffeine) was dispersed across a drivewayusing a shop vacuum operated as a blower. Method: To acquire wipe samples from the driveway, water-soaked, cotton swabs were rolledacross a 10 cm x 10 cm square delineated by a template in orthogonal directions to distribute theanalyte within the square uniformly about the swab for each sample collected. Wipe sampleswere taken at 84 sampling points of a 7 x 12 grid to prepare a map of the dispersed caffeine. Analyte from the edges of each swab was desorbed, ionized and mass analyzed by theDART/TOFMS. Chromatographic peak areas in the analyte ion chromatogram (m/z 195, MH+)for both edges of each swab were summed and plotted to provide a semi-quantitation map withdifferent colors for non-detect, low, moderate, high, and "visual analyte" levels. Preliminary data: Plugging of the cone orifice of the MS and carry over were initiallyproblematic. A particle in the orifice greatly reduced the ion abundances until it was dislodgedafter a few or more numerous swabs had been sampled. Plugging was avoided by making aninitial run with non-heated and non-energized helium gas. Easily dislodged dust particles fromthe driveway were blown off the swabs, while the analyte was not desorbed by the cold gas flow. Carry over was reduced by interspersing water-soaked swabs between analyte swabs to provide hot water vapor to clean condensed analyte from the region around the cone orifice. Furthercarry over reduction was observed in data collected a second time. Remaining carry over wasseen as an elevated baseline before or after each chromatographic peak when one or morepreceding swabs had high analyte levels. A macro written in Lotus 123 used the higher baselineto calculate each peak area. A second macro plotted the semi-quantitation map. A dynamicrange of 41 was estimated from triplicate wipe samples acquired from a mirror, which provided aclean, non-absorbent, and uniform surface upon which Nodoz solutions were deposited. A factorof 3.46 (cube root of 41) was used to define the semi-quantitation levels. A Vapur (IonSense),evacuated flange between the helium source and orifice increased the dynamic range to 300,reduced %RSDs (N=3) for wipe samples from the mirror from 27% to 10%, reduced themaximum/minimum ratio for triplicate measurements from 1.8 to 1.2, reduced carry over, andmay eliminate the need for the two preliminary runs. Future experiments with Nodoz dispersedacross the driveway and other surfaces will include the flange. Novel Aspect: Rapid plotting of semi-quantitation maps for dispersed chemicals based onDART/TOFMS data