PubMed · 10935056
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2000. Mutation causes sensitivity.. https://doi.org/10.1089/108729100413266
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An on-column trace enrichment method for CEC of dilute samples is presented. The method involves on-line preconcentration by frontal electrochromatography under conditions of strong solute binding to the stationary phase followed by a step-gradient elution electrochromatography with a mobile phase of high eluting strength. This method is tested with dilute samples of carbamate insecticides using capillary columns of 100-microm i.d. packed with a 5-microm octadecyl silica (ODS) stationary phase. The effectiveness of on-line preconcentration (i.e., zone narrowing) depends on the retention factor, k', of the analyte in the injection solvent as well as in the eluting mobile phase (i.e., the organic solvent content), the applied voltage during sample introduction, and elution and length of the introduced sample plug. Under optimal frontal and elution electrochromatography conditions, a 500-fold sensitivity increase is achieved for carbofuran (a carbamate insecticide) with a UV detector. The method is demonstrated with deionized and tap water samples spiked with carbamate insecticides.
A rapid, simple and sensitive high-performance liquid chromatographic (HPLC) assay has been developed for the simultaneous quantification of the HIV-protease inhibitors indinavir, amprenavir, ritonavir, saquinavir and nelfinavir in human plasma. The method involved the solid-phase extraction of the five drugs and the internal standard (I.S., verapamil) from 400 microl of human plasma. The HPLC analysis used a reversed-phase C18 analytical column and a mobile phase consisting of a gradient with 15 mM phosphate buffer (pH 5.75)-acetonitrile and UV monitoring. The method was linear over the therapeutic concentration range for the five HIV-protease inhibitors. The accuracy of the method ranged from 98.2 to 106.7% and the precision values ranged from 1.4 to 8.1% for intra-day precision and from 3.1 to 6.4% for the inter-day values.
The degradation of two oxime carbamate pesticides, oxamyl and methomyl, was investigated in anoxic solutions containing various metal ions and reducing agents. In reagent-free solutions, these carbamates degrade slowly via base-catalyzed elimination. Rates of carbamate degradation are accelerated by Fe(II), Cu(I), and Cu(II), but not by several other metal ions and reducing agents. In the presence of Fe(II), carbamates undergo a net two-electron reduction that is coupled to the sequential one-electron oxidation of two Fe(II) ions. The observed products are a substituted nitrile, methanethiol, and methylamine. A radical intermediate is inferred by polymerization of the radical scavenger acrylonitrile. Redox kinetics (i) vary with carbamate identity, (ii) exhibit first-order dependence on both Fe(II) and carbamate concentration, (iii) are relatively independent of pH, (iv) follow Arrhenius temperature dependence, and (v) are only indirectly influenced by the presence of O2. Coordinatively saturated Fe(II) complexes (Fe(II)EDTA2- and Fe(II)(CN)6(4-)) react with oxamyl at rates equal to and greater than hexaquo Fe(II), respectively, indicating that an inner-sphere Fe(II)-carbamate coordination complex is not required for electron transfer. Experimental results indicate that Cu(I) reduces the carbamates by the same mechanism as Fe(II) but at much higher rates. In contrast, Cu(II) acts as a catalyst for both elimination and reduction reactions.