Circumventing glass vial and diluent effects on solution stability of small molecule analytes during analytical method development and validation

Solution stability of analytes plays an important part in qualitative analysis, especially in conducting accurate, quantitative analyses. Sample diluents and glass vials as sample containers for HPLC analyses can play a critical role and should be evaluated during chromatographic method development. We have encountered several instances during pharmaceutical development where the glass vial/diluent combination has negatively impacted method performance. One case encompasses adsorption of piperazine, a secondary amine, to non-silanized glass vials, resulting in recovery failures during analytical method transfer. Two further cases describe the propensity for peracetylated C-aryl glucosides being subject chemical transformations relating to sample diluent. The first reports transesterification with methanol-based diluents and the second describes hydrolysis with acetonitrile/water diluents mediated by the mild alkalinity of certain brands of Type I borosilicate vials. A final case explores development of a related substance method, it was found that an impurity was prone to hydrolysis and another impurity with a primary amine tended to be adsorbed on glass vials. Diluents of appropriate pH and buffer strength were strategically selected to neutralize the mild alkalinity of the glass vials as well as to mitigate adsorption of the amine analyte on glass vials. As a result, excellent sample stability and reproducibility were achieved, regardless the quality and brand of Type I glass vials used. Here we present four case studies that demonstrate how the negative impact of Type I glass vials on those susceptible analytes can be effectively eliminated by using appropriate sample diluents, which is essential to ensure accurate analytical data and provide for a smooth method validation and transfer.