New Spectrophotometric Methods for the Determination of p-Aminosalicylic Acid in Tablets

Purpose: To develop a new spectrophotometric method with improved sensitivity and at higher wavelength for the determination of p-aminosalicylic acid in tablets. Methods: Two simple and sensitive spectrophotometric methods (methods A and B) were developed using p-dimethylaminobenzaldehyde (DAB), and p-dimethylaminocinnamaldehyde (DAC) as derivatizing reagents for the determination of p-aminosalicylic acid (PAS) in tablets. The derivatization was carried out using 3M HCl-KCl buffer for DAB and 5M HCl-KCl buffer solutions. Result: The new derivatives of PAS absorbed maximally with bathochromic shift to 460 and 555 nm in the linear concentration range of 0.4 - 2.0 mu g/mL with molar absorptivities of 2.4 x 10(4) and 3.8 x 10(4) L/mole/cm, respectively, compared to pure PAS which absorbed at lambda(max) of 264 nm with molar absorptivity 7.65 x 10(3) L/mole/cm in the linear concentration range of 2 - 10 mu g/mL. The developed methods were successfully applied to assay PAS in tablets with % recovery of 97.6 +/- 1.71 and 98.4 +/- 1.45 for methods A and B, respectively. Conclusion: Both PAS derivatives absorb in the visible spectral region. The presence of excipients in pharmaceutical preparations did not interfere in the determination of PAS as PAS-DAB and PAS-DAC derivatives. Both methods can be applied to determine PAS from bulk and various pharmaceutical dosage forms.