Comparison of two partial least squares infrared spectrometric methods for the quality control of pediculosis lotions

Two vibrational spectroscopy procedures have been developed and compared for the direct and simultaneous determination of piperonyl butoxide and tetramethrin, the active ingredients of alcoholic capillary lotions, for hair pediculosis diseases. Nine lotions, purchased from the Spanish market, were analyzed using both, attenuated total reflectance (ATR) and transmission FT-IR measurements, and based on the use of partial least squares (PLS) multivariate calibration. A reduced set of 15 matched standards (11 for calibration and 4 for validation) was employed using both measurement modes. The spectral wave number ranges between 1757 and 1712 cm−1 was selected to determine tetramethrin by both, transmittance and reflectance measurements. For the analysis of piperonyl butoxide the 1513–1479 cm−1 and 1576–1479 cm−1 regions were selected for ATR and transmission measurements, respectively. Results found for commercial samples compared well with those obtained by a liquid chromatography reference method that evidenced the applicability of the proposed strategy for the analysis of commercial formulations.