Abstract：A nonlinear model of consistency with derivative absorption in multiple components systems has been given. Model data were estimated by partial least squares method. A method for the simultaneous derivative spectrophotometric determination of two components with nonlinear partial least squares method was established. The method has been applied to the simultaneous determination of two components in compound sulfamethoxazole tablets. The average recoveries of sulfamethoxazole and trimethoprim in synthetic samples were 99.8% and 100.1%，and relative standard deviations were 1.3% and 1.6%，respectively. The results by nonlinear PLS method are significantly better than those by linear PLS method. The results for actual compound formulation agreed with those obtained by standard method.
Key words：Nonlinear partial least squares;Derivative spectrophotometry;Sulfamethoxazole;Trimethoprim;Compound sulfamethoxazole
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