M.J. del Nozal

Determination of pesticide residues in waters from small loughs by solid-phase extraction and combined use of gas chromatography with electron-capture and nitrogen-phosphorus detection and high-performance liquid chromatography with diode array detection

Abstract A procedure for the determination of pesticide residues in waters from small loughs surrounded by different crops has been developed. For this purpose, a solid-phase extraction procedure with octadecylsilane cartridges was used, optimizing the elution parameters as well as tthe breakthrough volume and the influence of the pesticide amount. The recoveries of the pesticides can be improved by about 10–20%. Extracts were analyzed either by gas chromatography with electron-capture and nitrogen-phosphorus detection or high-performance liquid chromatography with diode array detection to achieve a more reliable identification and determination of twenty-three pesticides from different chemical famiies, including triazines, phenylureas and organophosphorus.

Matrix effects in the determination of acaricides and fungicides in must by gas chromatography with electron-capture and nitrogen-phosphorus detection

Abstract The gas chromatographic determination of 12 pesticides, often used in viticulture, usually presents higher values than the real ones, arising from matrix effects, when must samples are analyzed. In order to reduce those errors, a method involving solid-phase extraction on octadecylsilane cartidges followed by a Florisil clean-up is developed. Moreover, a calibration with must extracts containing increasing amounts of pesticides and subjected to the same treatment as the samples also contributes to diminishing such errors.

High-performance liquid chromatographic determination of benomyl and carbendazim residues in apiarian samples☆

Simple procedures for the extraction and chromatographic determination of benomyl and carbendazim in honey, bees wax, larvae, bees and pollen are proposed. The fungicides were extracted from honey, larvae and bees using ethyl acetate, while methanol was more suitable for wax and pollen samples. Pollen extracts need a further clean-up step with n-hexane. The determination is carried out by reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection. The procedures have been applied to the analysis of benomyl on honey and larvae samples from hives whose bees were nourished with artificial food mixed with benomyl.

Applications of the Chiralpak AD and Chiralcel OD chiral columns in the enantiomeric separation of several dioxolane compounds by supercritical fluid chromatography.

Two chiral columns based on polysaccharide derivatives (Chiralpak AD and Chiralcel OD) have been tested for the chiral separation of several dioxolane compounds, using supercritical fluid chromatography. The compounds studied included ketoconazole and some of its precursors. The effect of the different modifiers and the pressure, on the chromatographic parameters was also evaluated. In general, the alcohol modifiers provided better results than acetonitrile, and all the compounds could be separated with these two columns, but the selection of the column depends on the kind of compound.

Multidetermination of PCBs and pesticides by use of a dual GC column-dual detector system

SummaryA new gas chromatographic method involving the use of two capillary columns, a switching valvue and electron capture-nitrogen-phosphorus detection, and allowing up to four retention characteristics per component to be obtained is reported.The proposed method was applied to the analysis for 123 compounds (13 PCBs and 110 pesticides), the determination limits and optimal measuring ranges of which are reported.The performance of the method was checked by analysis of certified standards and spiked samples, and was applied to the determination of the analytes in various water samples.

Separation of antifungal chiral drugs by SFC and HPLC: a comparative study

The enantiomeric separation of several compounds, including an antifungal drug and several of its precursors, using HPLC and SFC is described in this work. The columns employed were based on polysaccharide derivatives and the results show that most of the separations obtained by SFC are better, in terms of high resolution and short analysis time, than those obtained by HPLC. Only one compound could not be resolved using SFC but, in this case, HPLC provided baseline resolution.

Some observations on clean-up procedures using sulphuric acid and Florisil

The stability and recovery of 84 pesticides and 12 polychlorinated biphenyls after treatment with sulphuric acid have been studied. The results of these studies have been applied to the analysis of samples with different fat contents and compared with the results obtained using Florisil. The treatment with acid has a narrower field of application than treatment on a Florisil column.

Separation of triadimefon and triadimenol enantiomers and diastereoisomers by supercritical fluid chromatography.

The enantiomeric separation of triadimenol and triadimefon on a Chiralpak AD column using supercritical fluid chromatography, was studied in this work. The effect of different modifiers (methanol, ethanol and 2-propanol) was tested, with methanol and ethanol providing the best results for the enantiomeric separation of the two compounds. The enantioseparation of a mixture of triadimenol and triadimefon (six stereoisomers) was achieved in only 15 min using a gradient of ethanol, 200 bar, 35 degrees C and a flow-rate of 2 ml/min. The separation of triadimenol diastereoisomers on different achiral columns (diol, silica and ODS) was also investigated. In this case, the type of organic modifier to be used depended on the stationary phase, the Spherex Diol being the column that gave the best separation. Using this column, resolutions higher than 3 were obtained in analysis times of 5 min with any of the modifiers checked.

Separation of ketoconazole enantiomers by chiral subcritical-fluid chromatography

The separation of ketoconazole enantiomers by subcritical-fluid chromatography using an amylose-based column is described. Drastic changes in the resolution have been obtained for the different organic modifiers evaluated, with ethanol providing the best results. Other chromatographic parameters such as temperature, pressure and flow-rate have also been studied. The best results in terms of resolution and analysis time were obtained using 30% ethanol (containing 0.1% triethylamine and 0.1% trifluoroacetic acid), a pressure of 300 bar, a temperature of 35 degrees C and a flow-rate of 3 ml/min. Under these conditions the ketoconazole enantiomers are resolved in a short time (less than 7 min) and with high resolution (4.29).

HPLC Versus SFC for the Determination of Salbutamol Sulphate and Its Impurities in Pharmaceuticals

Abstract A method to determine salbutamol sulphate and six impurities: 5-formyl-saligenin, salbutamol ketone, salbutamol bis ether, isopropyl salbutamol, desoxysalbutamol sulphate and salbutamol aldehyde, using reverse phase high performance liquid chromatography (RP-HPLC) with diode array detection (DAD) is proposed. The best separation was achieved using a gradient of 0.1 M ammonium acetate pH 3.0 and acetonitrile. When the procedure was applied to the analysis of tablets and cough syrups, the versatility of the HPLC method was higher than one based on supercritical fluid chromatography (SFC). When using the later method the excipient difficulted the identification and quantification of some compounds in cough syrup samples.