A straightforward and sensitive method has been developed for the analysis of phosphorus-containing amino acid herbicides (glufosinate and aminomethylphosphonic acid, the major metabolite of glyphosate) in soil samples. For this purpose, the analytical features of two indocyanine fluorescent dyes, sulfoindocyanine succinimidyl ester (Cy5) and 1-ethyl-1-[5-(N-succinimidyl-oxycarbonyl)pentyl]-3,3,3,3-tetramethyl-indodicarbocyanine chloride, as labeling reagents for the determination of these herbicides by CZE with diode LIF detection were investigated. Practical aspects related to the labeling chemistry and CZE separation showed that the two probes behave similarly, Cy5 being the best choice for the determination of these herbicides on account of its higher sensitivity. The optimum procedure includes a derivatization step of the pesticides at 25 degrees C for 30 min and direct injection to CZE analysis, which is conducted within about 14 min using ACN in the running buffer. The lowest detectable analyte concentration ranged from 0.025 to 0.18 microg/L with a precision of 3.6-5.4%. These results indicate that indocyanine fluorescence dyes are useful as rapid and sensitive labels for the determination of these herbicides when compared with typical fluorescein dyes such as FITC and 5-(4,6-dichloro-s-triazin-2-ylamino) fluorescein, because they provide faster labeling reactions even at room temperature and the excess of reagent practically does not interfere the determination. Finally, the Cy5 method was successfully applied to soil samples without a preliminary clean-up procedure, and the herbicides were measured without any interference from coexisting substances. The recoveries of these compounds in these samples at fortification levels of 100-500 ng/g were 90-93%.
The suitability of an approach for extracting heuristic rules from trained artificial neural networks (ANNs) pruned by a regularization method and with architectures designed by evolutionary computation for quantifying highly overlapping chromatographic peaks is demonstrated. The ANN input data are estimated by the Levenberg-Marquardt method in the form of a four-parameter Weibull curve associated with the profile of the chromatographic band. To test this approach, two N-methylcarbamate pesticides, carbofuran and propoxur, were quantified using a classic peroxyoxalate chemiluminescence reaction as a detection system for chromatographic analysis. Straightforward network topologies (one and two outputs models) allow the analytes to be quantified in concentration ratios ranging from 1:7 to 5:1 with an average standard error of prediction for the generalization test of 2.7 and 2.3% for carbofuran and propoxur, respectively. The reduced dimensions of the selected ANN architectures, especially those obtained after using heuristic rules, allowed simple quantification equations to be developed that transform the input variables into output variables. These equations can be easily interpreted from a chemical point of view to attain quantitative analytical information regarding the effect of both analytes on the characteristics of chromatographic bands, namely profile, dispersion, peak height, and residence time.
A rapid, reliable method for the routine determination of phenol and 4-methylphenol in urine samples by liquid chromatography with peroxyoxalate chemiluminescence detection was developed. Phenols were first cleaned up by passing the sample through a LiChrolut EN sorbent column and then derivatized straightforwardly with dansyl chloride (15 min at room temperature) thanks to the micellar catalytic effect provided by Triton X-100 micelles. The derivatives were successfully separated in 15 min on a C18 analytical column and determined using an integrated derivatization chemiluminescence detection unit based on the bis(2,4,6-trichlorophenyl) oxalate-hydrogen peroxide system. Linear ranges from 3 to 500 microg L(-1), limits of detection at a signal-to-noise ratio of 3 from 0.3 to 0.5 microg L(-1) and relative standard deviations from 2.8 to 4.7% were obtained. The proposed method was applied to the assay of different human urine samples (healthy, smoker and petrol station worker volunteers) and free and total phenol and 4-methylphenol were determined. The proposed method surpasses other chromatographic alternatives for the determination of these phenols in terms of limit of detection and sample requirements for the analysis.
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