Flow-injection spectrophotometric determination of certain cephalosporins based on the formation of dyes

A flow-injection spectrophotometric method is described for the determination of cefadroxil (I) and cefotaxime (II). The method is based on the hydrolysis of the cephalosporin with sodium hydroxide whereby the sulfide ion is produced The latter is allowed to react with N,N-diethyl-p-phenylenediamine sulfate (N,N-DPPD) and Fe(III) and the blue color produced is measured at 670 nm (method A) Linear calibration graphs are obtained in the range 36.34-109.2 and 95.48-477.4 mug ml(-1) for I and II, respectively. The experimental limits of detection (three times the noise signal) are 0.036 and 0.048 mug ml(-1) for I and II, respectively. The total flow-rate is 5.3 ml min(-1) for both drugs. Alternately, the sulfide ion produced is allowed to react with p-phenylenediamine dihydrochloride (PPDD) and Fe(III), and the violet color produced is measured at 597 nm (method B). Linear calibration graphs are obtained in the range 0.5-400 and 0.5-450 mug ml(-1) for I and II, respectively. The limits of detection are 0.4 and 0.2 mug ml(-1) for I and II, respectively. The total flow-rate is 3 ml min(-1) for both drugs. The methods have been successfully applied to the analysis of some pharmaceutical formulations, particularly of the injection and capsule types. The relative standard deviation (RSD) (n = 10) at the 50 and 100 mug ml(-1) levels of I and II were 0.83-0.77 and 0.9-0.8% with N,N-DPPD and PPDD as reagents, respectively. Recoveries were quantitative; the results obtained agreed with those obtained by other reported methods. (C) 2001 Elsevier Science SA. All rights reserved.