Determination of the Active Principle in a Syrup by Spectrophotometry and Principal Component Regression Analysis. An Advanced Undergraduate Experiment Involving Chemometrics

An advanced analytical chemistry laboratory experiment concerning the determination of the mucolitic bromhexine in a commercial syrup is described. It involves the following steps: (i) preparing nine calibration mixtures and recording their absorption spectra in the region 285-348 nm, (ii) recording spectrophotometric data for four synthetic unknowns and two commercial samples, and (iii) processing them with the multivariate calibration technique of principal component regression (PCR). The theory of PCR is discussed, and a Visual Basic 5.0 for Windows 95/98 program is made available to students for data processing. The program allows students to perform cross-validation and to obtain and save relevant statistical information (root mean square deviation, correlation coefficient, and relative error of prediction), as well as calibration spectral factors and spectral residuals for each test sample, all of which illustrate the PCR technique in detail. The reagents used are low-cost and nontoxic; the experiment is simple and gives students an insight into a real practice that integrates chemistry, instrumentation, and computer techniques.