James N. Ogata

Potential problems with the use of distilled water in pesticide residue analyses

Abstract Precautions should be taken with distilled water that may be included in any scheme of analysis for pesticides, especially in the nanogram-picogram analytical range, to insure that the water has not been contaminated with organic components derived from the water distillation system. Ultimate analysis of the sample by gas chromatography, utilizing an electron capture detector, will record any contaminants present and they may confuse the interpretation of the pesticide analytical data. Preferably, an all-glass still unit which contains no plastic fittings of any type should be used. Some of the potential problems with distilled water that may occur if plastic or resin components are included in the distillation system are discussed in this report.

The effect of the column support material on the gas chromatographic resolution of methyl parathion, ethyl parathon, ethyl paraoxon, malathion, and malaoxon☆

Abstract The gas chromatographic capabilities of commercially available solid supports produces from diatomaceous earths were compared, using QF-1 silicone (FS 1265, 10 000 centistokes) as the stationary liquid phase. The relative efficiencies of the columns were evaluated from the chromatographic data obtained with the orga- phosphate compounds methyl parathond, ethyl parathon, ethyl paraoxon, malathion, and malaoxon. The data indicated that commericial methods for the preparation of solid supports have improved, but not to a degree sufficient to assure reproducible results with different batches of the same type of support. Each new batch of support should be examined for density and adsorptive characteristics before it is considered as a replacement for the column previously used.