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INTERLABORATORY STUDY OF A THERMOSPRAY-LIQUID CHROMATOGRAPHIC/MASS SPECTROMETRIC METHOD FOR SELECTED N-METHYL CARBAMATES, N-METHYL CARBAMOYLOXIMES, AND SUBSTITUTED UREA PESTICIDES
Citation:
Lopez-Avila, V. AND T. Jones-Lepp. INTERLABORATORY STUDY OF A THERMOSPRAY-LIQUID CHROMATOGRAPHIC/MASS SPECTROMETRIC METHOD FOR SELECTED N-METHYL CARBAMATES, N-METHYL CARBAMOYLOXIMES, AND SUBSTITUTED UREA PESTICIDES. Journal of the Association of Official Analytical Chemists International 76(6):1329-1343, (1993).
Description:
A thermospray-liquid chromatographic/mass spectrometric (TS-LC/MS) method was evaluated in an interlaboratory study for determining 3 N-methyl carbamates (bendiocarb, carbaryl, and carbofuran), 3-N-methyl carbamoyloximes (aldicarb, methomyl, and oxamyl), 2 substituted urea pesticides (diuron and linuron), and 1 ester of a substituted carbamic acid (carbendazim). The purpose of this study was to establish whether these 9 compounds can be reliably detected and quantitated with this method, and to establish the interlaboratory precision and accuracy of the method with currently available instrumentation. The study design was based on AOAC INTERNATIONAL's blind replicate design with balanced replicates. The samples consisted of solutions of the 9 test compounds in methanol at 3 concentrations that were unknown to the participating laboratories and that covered the linear range of the method. Nine volunteer laboratories participated in the study. Linear regression equations are presented that calculate the accuracy of the method, i.e., the percent recovery of each of the 9 compounds at any concentration within the range of concentrations tested (5-90 ug/mL for each compound, except carbendazim, for which the range was 1.25-22.5 ug/mL). The intralaboratory precisions of the TS-LC/MS method ranged from 6.5 to 33.1% relative standard deviation, depending on the compound. The interlaboratory method precisions ranged from 29.8 to 98.2% relative standard deviation over the concentration range tested. Analysis of variance indicates that for all compounds tested, the variation from laboratory to laboratory is greater than that attributed to analytical error displayed within laboratories. There are many operational parameters that could contribute to interlaboratory variability; one of them, the thermospray tip temperature, can play a major role in adduct formation and ion fragmentation in the case of thermally labile carbamate pesticides and, therefore, needs to be monitored and controlled carefully. The correlation of mass spectral data with the thermospray tip temperature was attempted using principal component analysis.