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A simple, accurate and precise spectrophotometric method has been proposed for the determination of eleven cephalosporins, namely; cefaclor monohydrate, cefadroxil monohydrate, cefalexin anhydrous, cefradine anhydrous, cefotaxime sodium, cefoperazone sodium, ceftriaxone sodium, ceftazidime penthydrate, cefazolin sodium, cefixime and cefpodoxime pro- xetil in bulk drug and in pharmaceutical formulations. The method depends on hydrolysis of the studied drugs using 0.5M NaOH at 100°C and subsequent reaction of the formed sulfide ions with NBD-Cl (4-chloro-7-nitrobenzo-2-oxa-1, 3-diazole) to form a yellow-colored chromogen measured at 390 nm. Different variables affecting the reaction (e.g. NaOH concentration, hydrolysis time, NBD-Cl concentration and diluting solvent) were studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9990- 0.9999) were found in the range of 5-160 μg mL-1 for all studied drugs. The limits of assay detection and quantitiation ranged from 0.289 to 5.867 and from 0.878 to 17.778 μg mL-1; respectively. The accuracy and precision of the proposed method were satisfactory. The method was successfully applied for analysis of the studied drugs in their pharmaceutical formulations and the recovery percentages ranged from 96.6 to 103.5%

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The combination of dynamic pH junction, sweeping (using borate complexation), and large volume sample stacking (LVSS) is investigated as three consecutive steps for on-line focusing in the sensitive quantitation of urinary nucleosides by CE-UVD. A low conductivity aqueous sample matrix free from borate and a high conductivity BGE (containing borate, pH 9.25) are needed to fulfill the required conditions for dynamic pH junction, LVSS, and sweeping. Parameters affecting the separation and the enrichment efficiency are studied such as buffer concentration, separation voltage, capillary temperature, sample composition, and sample injection volume. Prerequisite for the developed strategy is the extraction of the nucleosides from urine using a phenylboronate affinity gel, which is described to be a unique means for the selective enrichment of cis-diol metabolites under alkaline conditions. The impact of ionic constituents remaining in the eluate after extraction on focusing efficiency and resolution is investigated. The developed method is applied to the analysis of blank and spiked urine samples. Fundamental aspects underlying the proposed enrichment procedure are discussed. A detection limit as low as 10 ng mL(-1) is achieved. To the best of our knowledge, this LOD represents the lowest LOD reported so far for the analysis of nucleosides using CE with UV detection and provides a comparable sensitivity to CE/MS. Because of the high sensitivity, the proposed method shows a great potential for the analysis of nucleosides in human urine and other types of biological fluids.