Systematic internal standard variability and issue resolution: two case studies

Inclusion of dilution quality control samples in quantitative LC-MS bioanalysis

In LC-MS bioanalysis, sample dilution plays various roles, including bringing analyte concentrations within the validated/qualified dynamic range or alleviating matrix effect for accurate determination of the target analyte(s) in the intended study samples. Adherence to health authority requirements, incorporating good dilution practices, and timely demonstration of dilution integrity whenever samples are diluted in an analytical run are essential to ensure the reliability of bioanalytical results.

Evaluation, identification and impact assessment of abnormal internal standard response variability in regulated LC-MS bioanalysis

Internal standard (IS) plays an important role in LC-MS bioanalysis by compensating for the variability of the analyte of interest in bioanalytical workflow. Due to the complexity of biological sample compositions and bioanalytical processes, a certain level of IS response variability across a run or a study is anticipated. However, an extensive variability may raise doubts to the accuracy of the measured results and also suggest nonoptimal analytical method. In this current paper, recent publications and guidelines regarding IS response in LC-MS bioanalysis were thoroughly reviewed with focus on the evaluation, identification and impact assessment of 'abnormal' IS response variability. A systematic decision tree was proposed to facilitate investigation into abnormal IS response variability after each run.