ABSTRACT Ratio-spectra 1st- and 2nd-derivative spectrophoto-metry has been used for determining mixtures of cefoperazone sodium and cephalexin sodium. Calibration graphs were established up to 45 mg/ml for both cephalosporins, r ranging from 0.9998 to 0.9999. The 1st-derivative amplitudes at 223.5, 244 and 285.5 nm were selected for the assay of cefoperazone. Optimal wavelengths for determining cephalexin were 247 and 276.5 nm. The detection limits at 0.05 level of significance, calculated by statistical treatment of calibration data, ranged from 0.42 to 0.54 µg/ml for cefoperazone, and from 0.06 to 0.63 µg/ml for cephalexin. LOD and LOQ values were also calculated. These ranged from 0.40 to 0.58 and from 1.33 to 1.93 µg/ml, respectively, for cefoperazone, and from 0.10 to 0.61 and from 0.33 to 2.03 µg/ml for cephalexin. By the 2nd-derivative mode, lines of regression were linear at 215.5, 233.5, 251 and 277 nm, for determination of cefoperazone, with detection limits ranging from 0.18 to 0.58 µg/ml. For cephalexin linearity was obtained at 265 nm, with detection limit 0.11 µg/ml. LOD and LOQ values ranged from 0.20 to 0.56 and from 0.67 to 1.87 µg/ml, respectively, for cefoperazone. For cephalexin LOD 0.13 and LOQ 0.43 µg/ml. All the samples were tested for stability in solution and in the course of actual analysis, up to 24 hours from their preparation. The method was applied to synthetic mixtures and the RSD values ranged between 0.09% and 3.50% (cefoperazone), and between 0.10% and 3.71% (cephalexin). The method was also applied to vials and tablets for these drugs. The recoveries obtained were between 100.9% and 102.4% (cefoperazone), and 101.4% and 102.4% (cephalexin).
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