Quantitation of sulfamethazine in pork tissue by thin-layer chromatography.

Our earlier method to detect and quantitate sulfamethazine (SMZ) in milk at the 10 ppb level was modified to quantitate SMZ in pork tissue. Sulfabromomethazine (SBZ) is added to the tissue as an internal standard. SMZ and SBZ are extracted from the tissue into water as the supernatant of a centrifuged, aqueous homogenate and are cleaned up and concentrated by a series of solid-phase extractions. The sulfonamide-containing eluate is then separated on a silica gel thin-layer chromatographic plate. SBZ and SMZ are derivatized with fluorescamine, and their fluorescence is quantitated with a scanning densitometer. The limit of detection was estimated at 0.25 ppb (signal-to-noise ratio, 3:1). The average accuracy over the analysis range (0.54-21.8 ppb [micrograms/kg]) was 95.6% (standard deviation = 29.4%, n = 54).

Evaluation of restricted access media for high-performance liquid chromatographic analysis of sulfonamide antibiotic residues in bovine serum.

Three commercially-available high-performance liquid chromatographic columns packed with restricted access media were evaluated for suitability in multi-residue direct injection analysis at the ng/ml level. The internal surface reversed-phase and shielded hydrophobic phase columns were not sufficiently retentive to separate all analytes from the tail of the matrix peak. Coelution of some of the analytes was also observed with these columns. The semi-permeable surface column was significantly more retentive and selective, providing good separation of analyte and matrix peaks. With this column, an analytical protocol requiring no organic solvents was developed for the assay of six sulfonamides at a detection limit of 25 ng/ml.

Sedimentation field flow fractionation of mitochondrial and microsomal membranes from corn roots.

Sedimentation field flow fractionation (sed-FFF) is shown to be a valuable procedure for analysis of a wide variety of subcellular particle preparations. The principles underlying this relatively new separation procedure are described. Separation is based on differences between particles in mass and/or density. As in chromatography, the procedure involves relating on-line or off-line measurements made on the effluent from the separation chamber to the elution (retention) time. In this work effluents were monitored for absorbance at 254, 280, and/or 320 nm; collected fractions were assayed for protein content, total ATPase activity, and/or marker enzyme activities and, when appropriate, were examined by electron microscopy. The ratio of the absorbances at 254 and 320 nm was found to provide a sensitive measure of partial resolution of subcellular particles. Preparations containing all of the subcellular particles of corn roots (exclusive of nuclei, cell walls, and ribosomes), and fractions thereof enriched in mitochondria, microsomes, Golgi membranes, or plasma membranes, were examined by sed-FFF. The subcellular particles appear to remain largely intact. All of the particles observed had a mass less than 2 X 10(11) g/mol. All of the preparations were grossly heterogeneous with respect to effective mass distribution. This is due in part to heterogeneity with respect to the organelle of origin. In microsome preparations, components of low, medium, and high density were present in the unretained peak; the retained region had comparatively more high density particles. Plasma membrane preparations had a very wide effective particle mass distribution. The observations suggest that, in addition to its utility for analytic purposes, sed-FFF is likely to prove useful for micro-preparative fractionation of some subcellular particle preparations. Sed-FFF and density gradient centrifugation can be utilized as complementary methods.