Application constant center coupled with spectrum subtraction, ratio difference and ratio H-point standard addition methods for simultaneous determination of acetylsalicylic acid (ASA) and ascorbic acid (AA) in their binary mixtures

A combination of AA and ASA have been widely employed in pharmaceutical formulations for pain and fever relief including fevers associated with colds and flu and are, perhaps, some of the most consumed drugs in the world. The direct spectrophotometric methods have shown the spectral overlap of the main maxima during the simultaneous determination of these drugs [1]. Three simple, specific and accurate spectrophotometric methods were applied and validated for simultaneous determination of ASA and AA namely: constant center coupled with spectrum subtraction (CC-SS) [2], ratio difference (RD) and ratio H-point standard addition (R-HPSAM) [3-4]In this work, the mixtures of AA and ASA were determined by the three methods RD, R-HPSAM, and CC-SS. The effects of different parameters including the pH, concentration of the divisor, and wavelengths selection for the three methods were investigated. The accuracy, precision and linearity ranges of the proposed methods were determined, and the methods were validated and the specificity was assessed by analyzing synthetic mixtures containing the cited drugs. Linear range of (ASA) and (AA) obtained and respectively are: (10-30) and (3-30) mg L-1 for CC-SS and RD methods, and (10-25), (3-25) mg L-1 for RHPSAM. Influence of different interferences on selectivity of methods are considered. All proposed methods have admissible precision and accuracy for determination of ASA and AA in the cited drugs in tablets and their binary mixtures with different ratios in spiked water samples.