SPECTROPHOTOMETRIC DETERMINATION OF 6-AMINOPENICILLANIC ACID USING BROMOPHENOL-BLUE AND BROMOTHYMOL-BLUE

Two simple, selective and sensitive spectrophotometric methods are des cribed for the determination of 6-aminopenicillanic acid (6-APA). The methods are based on the reaction of 6-APA with either bromophenol blu e (BPB) or bromothymol blue (BTB), to give orange-red and green specie s, respectively. The coloured products are quantified spectrophotometr ically at 625 and 616 nm for BPB and BTB, respectively. The optimizati on of the different experimental conditions is described. No interfere nces from different beta-lactams and common degradation products were observed in the determination of 6-APA using BTB, while flucloxacillin , dicloxacillin, adrenaline, vitamin C, urea and common degradation pr oducts in any percentage interfere on using BPB only. The BTB method w as better than the BPB method, because of its wider range of determina tion (0.4-20 mugml-1 vs. 0.4-7.2 mug ml-1 on using BPB), higher molar absorptivity and Sandell sensitivity (3.27 x 10(3)1 mol-1 cm-1) and 0. 099 mug cm-2 vs. 2.82 x 10(3)l mol-1 cm-1 and 0.115 mug cm-2), greater stability (3 and 10 days on using BTB and BPB, respectively) and bett er selectivity. The results were compared with those given by the Offi cial United States Pharmacopeial XXI method.