Spectrophotometric study of the reaction mechanism between DDQ as π-acceptor and potassium iodate and flucloxacillin and dicloxacillin drugs and their determination in pure and in dosage forms

Two simple and accurate spectrophotometric methods are presented for the determination of β-lactam drugs, flucloxacillin (Fluclox) and dicloxacillin (Diclox), in pure and in different pharmaceutical preparations. The charge transfer (CT) reactions between Fluclox and Diclox as electron donors and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) π-acceptor and potassium iodate via oxidation reduction reaction where the highly coloured complex species or the liberated iodine have been spectrophotometrically studied. The optimum experimental conditions have been studied carefully. Beer's law is obeyed over the concentration range of 2–450 μg ml−1 for Fluclox and 10–450 μg ml−1 for Diclox using DDQ reagent and at 50–550 μg ml−1 for Fluclox and 50–560 μg ml−1 for Diclox using iodate method, respectively. For more accurate results, Ringbom optimum concentration range is calculated and found to be 6–450 and 15–450 μg ml−1 for Fluclox and Diclox using DDQ, respectively, and 65–550 and 63–560 μg ml−1 for Fluclox and Diclox using iodine, respectively. The Sandell sensitivity is found to be 0.018 and 0.011 μg cm−2 for DDQ method and 0.013 and 0.011 μg cm−2 for iodate method for Fluclox and Diclox, respectively, which indicates the high sensitivity of both methods. Standard deviation (S.D. = 0.01–0.80 and 0.07–0.98) and relative standard deviation (R.S.D. = 0.13–0.44 and 0.11–0.82%) (n = 5) for DDQ and iodate methods, respectively, refer to the high accuracy and precision of the proposed methods. These results are also confirmed by between-day precision of percent recovery of 99.87–100.2 and 99.90–100% for Fluclox and Diclox by DDQ method and 99.88–100.1 and 99.30–100.2% for Fluclox and Diclox by iodate method, respectively. These data are comparable to those obtained by British and American pharmacopoeias assay for the determination of Fluclox and Diclox in raw materials and in pharmaceutical preparations.