Studies on the elimination of interfering absorption in spectrophotometry of pharmaceutical prepartions Ⅲ.The orthogonal function method and its application to the determination of dihydrochlorothiazide in hypotensive tablets.

When the orthogonal function method is applied to spectrometric analysis, the interference of coexisting ingredients in pharmaceutical preparations may be eliminated without any preliminary separation. This method is simple and accurate which is applied to the determination of dihydrocholorothiazide in hypotensive tablets.It has been found that with a six-point polynomial over the 261 to 281 nm at 4nm intervals,P2, the coefficient of the quadratic polyomical, was proportional to the concentration of dihydrochlorothiazide and independent of the concentration of the coexisting ingredients` in the tablets. This manual spectrophotometer(751G) has been used, the mean recovery of dihydrochlorothiazide is 99.61±0.62% (at the 95% confidence level) and the relative standard deviation is 1.1%(n=14).