DETERMINATION OF TERNARY MIXTURES OF ANTIBIOTICS, BY RATIO-SPECTRA ZERO-CROSSING FIRST-DERIVATIVE AND 3RD-DERIVATIVE SPECTROPHOTOMETRY

The ratio-spectra zero-crossing first- and third-derivative spectrophotometry have been used for determining ternary mixtures of penicillin-G sodium, penicillin-G procain and dihydrostreptomycin sulphate salts. The procedures are accurate, nondestructive and do not require resolutions of equations. In both methods, calibration graphs are linear, with zero-intercept, up to 30 mu g ml(-1) of penicillin-G sodium and penicillin-G procain, and up to 42 mu g ml(-1) of dihydrostreptomycin sulphate. r = 0.9999 in each instance. Working wavelengths, 218.5, 211 and 236 nm, respectively, in the first-derivative mode, and 222.5, 311.5 and 242 nm in the third-derivative mode. Detection limits for each drug at p = 0.01 level of significance were calculated to be 0.058, 0.010 and 0.014 mu g ml(-1) and 0.14, 0.012 and 0.34 mu g ml(-1), in the first- and third-derivative methods, respectively. Both methods apply favourably to either laboratory mixtures or commercial injections.