Simultaneous spectrophotometric determination of difloxacin and enrofloxacin in urine samples by partial least squares regression (PLS) and direct orthogonal signal correction-partial least squares regression (DOSC-PLS) methods

Simultaneous determination of difloxacin and enrofloxacin using two chemometric methods, partial least squares regression (PLS) and direct orthogonal signal correction-partial least squares regression (DOSC-PLS) is described in this paper. The simultaneous determination of these drugs is difficult due to spectral interferences. The calibration graphs were linear in the range of 1-10 μg mL-1 and 1-9 μg mL-1 with detection limits of 0.52 and 0.15 μg mL-1 for difloxacin and enrofloxacin, respectively. The experimental calibration matrix was designed with 25 mixtures of these drugs. The PLS and DOSC-PLS were used for multivariate calibration of spectrophotometric data. The root mean square error of prediction (RMSEP) for applying the two methods to 8 synthetic samples in the linear calibration ranges for difloxacin and enrofloxacin was 0.1499 and 0.2833 for PLS, 0.0753 and 0.0436 for DOSC-PLS respectively. The relative standard error of prediction (RSEP) for difloxacin and enrofloxacin was 3.5214 and 7.6757 with PLS, 1.7694 and 1.1809 for DOSC-PLS, respectively. The DOSC-PLS method was found to be more accurate than PLS method providing better recoveries and lower RMSEP and RSEP values. The DOSC-PLS method was successfully applied to simultaneous determination of difloxacin and enrofloxacin in urine samples.