Effect of Sample Preparation and Chromatographic Conditions on Background Signal

The HPLC-UV method is widely used for quantitative analysis of drug substances found in biological samples obtained in pharmacokinetics studies, bioequivalence studies, or during therapeutic drug monitoring. The main limitation is associated with a significant background effect of biological matrixes, limiting the sensitivity of HPLC-UV methods. The aim of the study was to evaluate sample preparation and chromatographic conditions in terms of background signal level during HPLC-UV analysis of blood plasma. Material and methods: three types of blood plasma (rat, rabbit and human), three chromatographic modes, and three detection wavelengths were used to assess the effect of the precipitation agent, centrifuge conditions, and the inclusion of the solid-phase extraction (SPE) step into the sample preparation procedure on the background signal level during HPLC-UV analysis. Results. It was established that the background signal was practically unaffected by the chromatographic mode, centrifugation intensity, or introduction of the SPE step. The background signal levels for human and rabbit blood plasma tended to be lower than that for rat blood plasma. The factors that had the greatest effect on the background signal level were the choice of the precipitation agent during sample preparation, and the detection wavelength. It was shown that acetonitrile is preferable to methanol, and that the near UV region should be avoided. Conclusions. The identified key aspects of sample preparation procedures and chromatographic conditions can be used in the development and validation of bioanalytical methods for preclinical and clinical studies.