Development of a high-performance liquid chromatography retention index scale for toxicological drug screening

An efficient and practical analytical method for correcting HPLC retention data has been produced using an HPLC diode-array UV detector system. The system is based on retention indices (RI) and is to be used primarily for the identification of toxicologically relevant drugs involved in clinical and forensic toxicology. The RI correction method was chosen as it provided a slightly greater degree of reproducibility than using relative retention time (RRT), particularly for acidic and neutral drugs. Development of the system involved the establishment of the optimal chromatographic conditions and extensive studies of the stability of the system. An acetonitrile gradient elution was used with RI values determined by interpolation from a series of specifically chosen basic and acidic/neutral marker drugs which eluted at regular intervals to produce a linear RI scale. It was found that two separate RI scales were required for basic and acidic/neutral drugs. The use of multiple drug markers as primary retention index standards had not been previously applied to HPLC general drug screening and comparison with a recently published database suggests that the system may also provide improved selectivity.