PubMed · 798518
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S J Mulé. 1976. Methodological problems in drug interactions.. https://doi.org/10.1111/j.1749-6632.1976.tb27924.x
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The determination of organophosphorus pesticides in fruits by size-exclusion chromatography (SEC) on a polystyrene column coupled on-line to a gas chromatography (GC) system was unsatisfactory as a result of interfering peaks in GC. A liquid chromatography step on silica gel was therefore inserted between the SEC and GC steps to filter out polar by-products. Samples of fruit (apples, grapes and kiwi fruits) were extracted, then the extract filtered or centrifuged and injected into an automated on-line SEC-liquid chromatography-GC-flame photometric detection. Recoveries were about 95% and the detection limits about 1 ng/g.
Under the sponsorship of the World Health Organization (WHO), an interlaboratory calibration on the analysis of PCDD/PCDFs in human milk and blood was carried out which included 19 laboratories from 14 countries. The study design involved the analysis of three samples of each matrix in triplicate. Selected samples were spiked with native standards of certain 2,3,7,8-substituted congeners at concentrations known only to WHO staff. The study design resulted in approximately 4000 individual pieces of PCDD/PCDF data generated by a variety of analytical methods, at various concentrations, and by laboratories of widely different experience. This was, by considerable margin, the largest study which allowed for the direct comparison of laboratory and method performance. The results of statistical analysis of this data base addresses the effect on data quality of clean up methods, instrumental methods, analyte concentration, laboratory QA programs, and laboratory experience. The study has shown that the laboratory is the single most important determinant of data precision and accuracy. The method of analyte enrichment (sample clean up), analyte measurement [gas chromatography/mass spectrometry (GC/MS) protocol], and analyte concentration have weaker correlations with data quality.
A gas chromatographic method for the determination of the nicotine metabolite trans-3'-hydroxycotinine is described. The method involves conversion of the metabolite to the tert.-butyldimethylsilyl derivative, chromatography on a fused-silica capillary column, and determination using nitrogen-phosphorus detection or electron ionization mass spectrometry with selected ion monitoring. A structural analogue, trans-3-hydroxy-1-methyl-5-(2-pyridyl)pyrrolidin-2-one (trans-3'-hydroxy-ortho-cotinine), was used as an internal standard. Using selected ion monitoring, good precision and accuracy were obtained for determination of trans-3'-hydroxycotinine in urine over the concentration range 10-10,000 ng/ml. There was a good correlation between concentrations determined by selected ion monitoring and by nitrogen-phosphorus detection in urine of smokers, although low concentrations determined using nitrogen-phosphorus detection tended to be somewhat higher, suggesting some interference from urinary constituents. Concentrations and 24-h excretion of trans-3'-hydroxycotinine in the urine of 22 cigarette smokers are reported and compared to concentrations and excretion of nicotine, cotinine, nicotine 1'-N-oxide, nornicotine, and cotinine N-oxide.