Capillary electrophoresis of some tetracycline antibiotics coupled with reductive fast cyclic voltammetric detection.

The separation and quantitative performance parameters for tetracycline, chlortetracycline and oxytetracycline antibiotics were investigated by capillary zone electrophoresis coupled with fast cyclic voltammetric detection. Optimization of pH and complexation with a boric acid-sodium tetraborate buffer provided good resolution of all compounds. Detection by electrochemical reduction using fast on-line cyclic voltammetric detection with a Hg-film-microm electrode gave detection limits (2 x peak-to-peak baseline noise) of 7 x 10(-7) mol/l for tetracycline and chlortetracycline, and 1.5 x 10(-6) mol/l for oxytetracycline. The influence of electrode material, potential range and scan rate was examined and discussed. Optimal electrochemical detection was obtained at a Hg-film electrode with a waveform that consisted of an initial constant potential of -0.6 V for 200 ms followed by a cyclic voltammetry (CV) scan at 300 V/s from - 0.6 V to a vertex potential of 1.7 V. The analytical signal was obtained by plotting the integrated values of the CV current from each applied waveform as a function of time. The calibration plot (peak areas) for each separated peak was found to be linear over three-orders of magnitude.

Analysis of streptomycin and dihydrostreptomycin in milk by liquid chromatography.

A method developed for the determination of the aminoglycoside antibiotics streptomycin and dihydrostreptomycin in tissues was applied to the analysis of fluid milk. Samples are extracted with 3.6% perchloric acid, and then injected onto a trace enrichment column, from which they are eluted onto a reversed-phase analytical column. The analytes are detected by fluorescence following postcolumn derivatization with 1,2-naphthoquinone-4-sulfonic acid. Recovery of analytes was in the range of 50-65% for skim or partially defatted fluid milk, while recoveries for homogenized whole milk were lower. Limits of quantitation were 10 ppb for streptomycin and 20 ppb for dihydrostreptomycin.

Determination of streptomycin and dihydrostreptomycin in animal tissue by on-line sample enrichment liquid chromatography.

A method for the determination of streptomycin and dihydrostreptomycin in pork and bovine muscle and kidney was developed. Dilute perchloric acid solution is used to precipitate proteins and extract the analytes from the tissue. The extract is loaded onto a cation-exchange, solid-phase extraction column, and the drugs are eluted with pH 8 phosphate buffer. The eluant is chromatographed by using an on-line column enrichment liquid chromatographic system with postcolumn derivatization using 1,2-naphthoquinone-4-sulfonic acid and detection by fluorescence. The recoveries were 61.1% (coefficient of variation [CV], 7.3%) for streptomycin and 55.3% (CV, 8.2%) for dihydrostreptomycin. The detection limits were 10 ppb for streptomycin and 20 ppb for dihydrostreptomycin.

Determination of tylosin and tilmicosin residues in animal tissues by reversed-phase liquid chromatography.

A method for the simultaneous determination of tylosin and tilmicosin residues in animal tissues is reported. Solid-phase extraction columns are used to isolate the drugs from tissue extracts. Determination is accomplished by reversed-phase liquid chromatography with UV detection at 287 nm. Mean recoveries from spiked tissues were 79.9% (coefficient of variation [CV], 8.1%) for tylosin and 92.6% (CV, 8.7%) for tilmicosin. Detection limits for tylosin and tilmicosin were 0.020 and 0.010 ppm, respectively.