Enhancing LC/ESI-MS/MS Throughput for Plasma Bile Acid Assay by Derivatization-based Sample-Multiplexing.

Liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) enables the accurate and precise quantification of various analytes at very low concentrations, but it has room for improvement in analysis throughput. Multiplexing of samples in the same injection could be a promising procedure for enhancing the analysis throughput. This could be achieved by derivatization of the multiple samples with multiple isotopologous reagents. In this study, a sample-multiplexed LC/ESI-MS/MS assay using the 1-[(4-dimethylaminophenyl)carbonyl]piperazine (DAPPZ) isotopologues (2H0-, 2H3-, and 2H6-forms) was developed and validated for the simultaneous determination of primary bile acids in three different plasma samples in a single run. The developed method had satisfactory intra- and inter-assay precisions (≤ 2.3 and ≤ 4.2%, respectively) and accuracy (99.0 - 100.3%), and could reduce the total LC/ESI-MS/MS run time by more than 60% for 42 samples compared to the conventional method. Thus, the derivatization with the DAPPZ isotopologues worked well for enhancing the throughput of the LC/ESI-MS/MS assay of the bile acids.

A Method for Quantification of Tetrahydroglucocorticoid Glucuronides in Human Urine by LC/MS/MS with Isotope-coded Derivatization.

The determination of urinary tetrahydroglucocorticoid (THGC) glucuronides might prove helpful in the diagnosis, pathophysiological analysis and assessment of the therapeutic efficacy of the diseases caused by abnormal cortisol secretion. We developed and validated a method for the determination of the THGC glucuronides in human urine using liquid chromatography/electrospray ionization (ESI)-tandem mass spectrometry not requiring enzymatic hydrolysis. The method employed a derivatization using an ESI-enhancing reagent for carboxylic acids, 1-[(4-dimethylaminophenyl)carbonyl]piperazine (DAPPZ), and its isotopologue, 2H4-DAPPZ. The deproteinized urine samples were derivatized with DAPPZ. The 2H4-DAPPZ-derivatized standards of known amounts were then added to the DAPPZ-derivatized urine samples and served as the internal standards. The DAPPZ-derivatization enhanced the assay sensitivity and reduced the sample volume, and the use of 2H4-DAPPZ significantly improved the assay accuracy. The developed method enabled the separate quantification and profiling of the urinary THGC glucuronides and had a satisfactory application for the real sample analysis.