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THE DETERMINATION OF NON-PESTICIDAL AND PESTICIDAL ORGANOTIN COMPOUNDS IN WATER BY GAS CHROMATOGRAPHY WITH [PULSED] FLAME PHOTOMETRIC DETECTION (GS/PFPD): THE EFFECTS OF "MASS" DISCRIMINATION
Evans, O M., P Kauffman, AND J N. Morgan. THE DETERMINATION OF NON-PESTICIDAL AND PESTICIDAL ORGANOTIN COMPOUNDS IN WATER BY GAS CHROMATOGRAPHY WITH [PULSED] FLAME PHOTOMETRIC DETECTION (GS/PFPD): THE EFFECTS OF "MASS" DISCRIMINATION. Presented at American Chemical Society 36th Central Regional Meeting, Indianapolis, IN, June 2-4, 2004.
The goal of this research effort is development of analytical methods for the determination of compounds selected for the 1998 Contaminant Candidate List (CCL) [Note: chemicals on the CCL are denoted below with a single asterisk, *. Chemicals with a double asterisk, **, are used as Internal Standards (Recovery and Quantitative).]. These may include selected non-pesticidal* , pesticidal, and other types of organotin compounds: monomethyltin trichloride*, dimethlytin dichloride*, trimethyltin trichloride, monobutyltin trichloride*, dibutyltin dichloride*, tributyltin chloride, phenyltin trichloride, diphenyltin dichloride, triphenyltin chloride, tricyclohexyltin, tripropyltin chloride**, tetrapentyltin**, tetrabutyltin**, etc.. The method(s) should be adequate for gathering occurrence data under the Unregulated Contaminant Monitoring Rule (UCMR) and should be applicable to / for compliance monitoring in the event selected non-pesticidal and / or pesticidal organotins become regulated contaminants under the Safe Drinking Water Act (SDWA).
Capillary gas chromatography with GC/PFPD was used in the development of analytical methodology for determining both non-pesticidal and pesticidal organotin compounds in drinking water and other aqueous matrices. The method involves aqueous ethylation of organotin analytes with sodium tetraethylborate, extraction into hexane and analysis by GC/PFPD. A PFPD is an equimolar response detector, i.e., the same quantity of tin reaching the detector should produce the same response for all organotin compounds. In general, the lower boiling and lower molecular weight non-pesticidal organotin compounds give analytical signal responses that are linearly related to the concentration of the analytes over the range studied. The higher boiling and higher molecular weight pesticidal organotin analytes, on the other hand, can give erratic peak area and peak height responses that are too small, and may result in non-linear signals, and lower slopes, as compared to their more volatile counterparts over the same concentration range. The fully alkylated, non-derivatized, quantitative internal standards, tetrabutyltin and tetrapentyltin, added to the extract in the same relative amount, may yield divergent peak area and peak height responses. An investigation of the needle handling techniques, i.e., "cold needle" injection vs. "hot needle" injection and injection speed, reveal the problem may be, in part, attributable to "needle" or "mass" discrimination between the [more volatile] lower boiling and lower molecular weight non-pesticidal organotins and some of the higher boiling and higher molecular weight pesticidal organotin compounds. Additionally, data will be presented to show: a) a minimum reaction time of 5 minutes for sodium tetraethylborate alkylation, b) derivatization yields greater than 50%, subsequent to alkylation, for most of the organotins, c) multiple internal standard calibration and calibration checks over a 21 day period, d) results of the analysis of very hard water [hardness: 325 to 350 mg/L], fortified with organotin analytes from 2.5 to10 parts-per-trillion, yielding recoveries ranging from to 71 to121% for 9 out of 10 compounds, e) method detection limits for organotins, ranging from 0.01 to 0.18 parts-per trillion, using the EPA single concentration procedure vs. the alternative Hubaux-Vos calibration based graphical approach, and f) the analytical response and correlation coefficient data for each analyte over the desired concentration range of 0.2 to 10.0 parts-per-billion, subsequent to extraction and concentration.