Simultaneous determination of salicylamide, acetylsalicylic acid and salicylic acid by multi-wavelength spectrophotometric methods.

Several graphical methods (zero-crossing and multiple linear regression analysis) are described to carry out the simultaneous determination of salicylamide (S) and acetylsalicylic acid (ASA) in the ranges 1.0-30.0 and 2.0-25.0 mu g/ml, respectively; with detection limits of 0.15 and 0.19 mu g/ml and quantitation limits for both drugs, in the presence of the maximum of the other analyte, of 4.0 and 2.0 mu g/ml for the former and later method, respectively. A multi-wavelength regression method was also used to determine the aforementioned binary mixture and the ternary mixture of salicylamide, salicylic acid (SA) and acetylsalicylic acid in the same ranges with equal detection limits for the binary mixture, and quantitation limits of 4.0 for S and SA, and 5.0 for ASA in the presence of the maximum of the others. Both graphical and numerical methods were found to provide good results in the resolution of several binary and ternary synthetic mixtures, even when the different compounds showed overlapped spectra. However, the MULTIC program allows the determination of higher analytes concentration ratios. When the graphical methods were used, errors were higher than 5% for salicylamide/acetylsalicylic acid ratios equal to 10/1 or 1/10. This shortcoming was not observed when the multi-wavelength regression method was used.