Purity assessment and resolution of tetracycline hydrochloride samples analysed using high-performance liquid chromatography with diode array detection

Abstract High-performance liquid chromatography with diode array detection (HPLC–DAD) was used for the analysis of a tetracycline hydrochloride sample (TC-HCl). The analytical search for impurities in TC-HCl is complicated, because the standards are not always available and because unexpected impurities are produced by new mutants during fermentation. Due to this it is useful to check the purity of the peaks in the chromatogram even when it is obtained with an optimised analytical technique. The homogeneity of the individual peaks in the HPLC–DAD chromatogram was checked using chemometric methods such as the orthogonal projection approach (OPA) and the fixed size moving window evolving factor analysis approach (FSW-EFA). After the selection of the number of components, the experimental data were resolved in the pure component spectra and the individual concentration profiles. The multivariate curve resolution alternating least-squares approach (MCR-ALS) was applied for this purpose on the single HPLC–DAD chromatograms (two-way data) and on sets of such chromatograms (three-way data).