Ruggedness testing of liquid chromatography-tandem mass spectrometry system components using microbiome-relevant methods and matrices

Recently, an opportunity to perform a broad ruggedness assessment of our liquid chromatography-tandem mass spectrometry (LC-MS/MS) system presented itself during the analytical planning phase of a large-scale human fecal microbiome study. The specific aim of this project was to study the microbial-mediated metabolism of a targeted set of bile acids/salts by mixed bacterial communities cultured from the feces of 12 healthy volunteers when grown in a custom growth medium and following exposure to different clinically-relevant antibiotics. The magnitude of this study offered a rare opportunity to significantly stress procedures and LC-MS/MS system components comprised in our bile acid/salt targeted metabolomics method. With this second specific aim in mind, we modified the sample analysis plan to include a series of figure-of-merit (FoM)-based tests that are commonly used in regulated bioanalytical labs to assess LC and MS system ruggedness for a specific assay - these FoM-based testing parameters were monitored continuously over the course of sample analysis and the results are presented in this report. In total, the assessment included 1206 sequential injections (180 calibration standards, 136 blank-internal standard samples, and 890 diluted medium samples) that took place over 8-days. Completion of the 8-days of non-stop sample analysis revealed no critical hardware or software failures, and the analysis of the FoM-based tests indicated no observable degradation of system performance over the number of samples and time tested. The FoM-based test metrics presented may be used as a template to assess the ruggedness of any LC-MS/MS-based targeted metabolomics workflow.

The impact of hemolysis on stability of N-desethyloxybutynin in human plasma

Aim: Stability must be evaluated before quantitation of drugs or metabolites concentrations in biological matrices. We reported a case study where instability of a drug metabolite was mediated by hemolysis. Materials & methods: The instability of both enantiomers of N-desethyloxybutynin was observed in hemolyzed plasma stored at -20°C. The investigations indicated that heme-mediated oxidation converted the metabolite to its N-oxide. Storing samples under lower temperature (-50°C or below) or treatment with the antioxidant ascorbic acid stabilized the metabolite. Conclusion: The evaluation of the stability of some analytes in a hemolyzed sample is crucial as it may negatively impact incurred sample reanalysis or pharmacokinetic profiles on highly hemolyzed samples.

Ocular bioanalysis: challenges and advancements in recent years for these rare matrices

There are many ocular diseases still presenting unmet medical needs. Therefore, new ophthalmologic drugs are being developed. Bioanalysis of eye compartments (along with plasma and other tissues) is important to determine exposure of the target organ to the drug and to help interpret local pharmacological or toxic effects. This review article identifies several challenges that occur within ocular bioanalysis. They include sample collection and preparation, analytical issues, sourcing control matrix, data interpretation and regulatory requirements. It summarizes how these challenges have been recently addressed, how research has advanced and which questions remain unanswered. Recommendations are made based on the literature and our practical experience within ocular bioanalysis and future perspectives are discussed.