Solute Retention in Column Liquid Chromatography. II. Optimization of Mobile-Phase Compositions

Determination of fatty acids in fish oil dietary supplements by capillary chromatography with laser-induced fluorescence detection

The 4-bromomethyl-7-methoxycoumarin derivatives of 14 saturated and unsaturated fatty acids, including the omega-3 fatty acids, were separated by reversed-phase liquid chromatography and detected by laser-induced fluorescence. Baseline resolution was obtained by using a high-efficiency packed capillary column with 240,000 theoretical plates, together with a systematic optimization of the mobile phase composition. The retention indices of the fatty acid derivatives correlated well with a predictive empirical model, showing accuracy better than 0.46% relative error and reproducibility better than +/- 0.1% relative standard deviation. The physiologically important fatty acids with 12-22 carbon atoms and 0-6 double bonds were determined at the femtomole level in fish oil dietary supplements by using this methodology.

Oxidative detection of coulometrically reduced organonitro pesticides in reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic system is presented for determination of organonitro pesticides, metabolites and industrial chemicals having a variety of chemical structures. The compounds are chromatographed on a C8 column with an acetonitrile-aqueous ammonium monochloroacetate gradient. The chromatographic responses of the compounds are monitored indirectly by oxidative detection of the coulometrically reduced organonitro functionality by means of a porousgraphite detector. Three nitrophenols (2,4-dinitrophenol, 4,6-dinitro-o-cresol and dinoseb), a dinitrophenyl aliphatic ester (binapacryl) and a nitroaniline (dicloran) were detected at low nanogram levels (3-10 ng for 50% recorder full-scale deflection). This technique overcomes the problems of high background currents and oxygen interference, observed in the direct reductive detection of organonitro compounds.