Page - (000108) - in Biomedical Chemistry: Current Trends and Developments

used as IS. However, when not possible, a compound structurally similar to the analyte and sharing identical behaviors during the entire bioanalytical protocol is used. It is noteworthy that various animal species and matrices are frequently investigated within pre-clinical studies, requiring significant effort to fully validate all the assays if they are independently developed to each species/matrix. In these situations, a partial validation or cross validation may be sufficient to manage time and resources more efficiently at this stage. Using cross validation, the analyst will rely on the ability of the full validation protocol established in the matrix of one species to predict the concentrations of NCE in a similar matrix of other species. However, the scope of partial validation must be justified and certain parameters must be assessed separately in the sample type that is being subjected to cross validation (FDA, 2001; EMA, 2011), including stability and selectivity. In essence, although a significant shortcut of the procedures is undertaken, it cannot compromise either the data quality or the data integrity. As the molecule advances into clinical trials, the assays developed to analyze human samples need to be more sensitive, rugged and robust to some small variations in matrices. Particularly in phase I clinical trials, high sensitivity is demanded to ensure that the lowest effective doses can be identified. In fact, if the samples are from first-time-into-humans studies, resolution is more important than throughput since the number of samples is low but the fate of the compound is unknown, requiring complete resolution of the analyte peak from all eventual matrices interferences. Additionally, stability must be evaluated again because matrices are distinct from those analyzed in pre-clinical stages. Similarly, it is also required to evaluate the method selectivity, also considering the metabolites formed in vivo and drugs probably co- prescribed to the patients in order to avoid their interference with the drug candidate under investigation. Accordingly, it is desirable to develop flexible and robust assays that enable minor alterations in chromatographic conditions to circumvent eventual interfering peaks if necessary. In current practice, MS detection is employed in the analysis of the