Application of Azure A in the Spectrophotometric Determination of Penicillin Drugs

A simple, accurate, and rapid method for the quantitative analysis of two penicillin drugs is developed. The method is based on the formation of a blue penicillin-azure A ion pair that can be extracted into chloroform in phosphate-citric acid buffer of pH 2.6-6.8 at room temperature (25 + 2oC). The molar absorptivities for sodium penicillin G and potassium penicillin V at 660 nm are 6.74 x l03 and 3.87 x l04 M-l cm-l, respectively. Beer’s law was obeyed over the concentration range of 3.5 75 ppm for sodium penicillin G and 3.0 50 ppm for potassium penicillin V. The optimum concentration ranges evaluated by Ringbom’s method and the Sandell’s sensitivities for sodium penicillin G and for potassium penicillin V were 7.0 68 ppm and 6.0 45 ppm, and 76 ng cm-2 and 24 ng cm-2, respectively. Maximum absorbance of the solution was obtained almost instantaneously and was stable for several days. The Job’s method of continuous variations indicated that a single l:l ion pair species was extracted. The relative error was +2%.