Comparative study of partial least squares and a modification of hybrid linear analysis calibration in the simultaneous spectrophotometric determination of rifampicin, pyrazinamide and isoniazid

Two multivariate methods, the classical partial least squares (PLS-1) and a modification of the novel hybrid linear analysis (HLA/XS method), are described for the simultaneous determination of rifampicin, pyrazinamide and isoniazid. A calibration set is constructed, using a combined central composite and factorial design (15 objects), in the range of concentrations comprised between 0 and 15µg/ml for rifampicin and pyrazinamide, and 0-10µg/ml for isoniazid. The proposed methods are satisfactorily applied to the determination of mixtures of these drugs. The precision expressed as R.S.D. (%) is calculated for both models. HLA/XS and PLS optimized calibrations are tested and compared in the analysis of several pharmaceutical formulations. The calculation of the net analytical signal using a modified HLA/XS method, allows us the determination of several figures of merit, as selectivity, sensitivity, analytical sensitivity and limit of detection of the proposed multivariate calibration. PLS-1 and HLA/XS calibration show similar ability to determine rifampicin and pyrazinamide but slightly worse results for isoniazid are obtained when using HLA/XS.