Eliminating Preparation of Multisample External Calibration Curves and Dilution of Study Samples Using the Multiple Isotopologue Reaction Monitoring (MIRM) Technique in Quantitative LC-MS/MS Bioanalysis

Preparation of multisample external calibration curves and dilution of study samples are critical steps in bioanalytical sample processing for quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) based bioanalysis of small-molecule compounds, biotherapeutics, and biomarkers, but they can be time-consuming and prone to error. It is highly desired to simplify or eliminate these two steps in order to improve the assay throughput and robustness. While multisample external calibration curve preparation using authentic matrices can be eliminated with a previously reported in-sample calibration curve (ISCC) approach using multiple isotopologue reaction monitoring (MIRM) of a stable isotopically labeled (SIL) analyte, dilution of study samples is still inevitable due to limited LC-MS/MS assay ranges. In this work, a one-sample multipoint external calibration curve and isotope sample dilution, both using MIRM of an analyte, for quantitative LC-MS/MS based bioanalysis are proposed and demonstrated. By spiking a known amount of an analyte into one blank authentic matrix sample, a one-sample multipoint external calibration curve in an authentic matrix can be established on the basis of the relationship between the calculated theoretical isotopic abundances (analyte concentration equivalents) and the MS/MS responses in the corresponding MIRM channels. This one-sample multipoint external calibration curve can be used in the same way as the traditional multisample external calibration curve for quantitative LC-MS/MS-based bioanalysis. As isotopic abundance in each MIRM channel can be calculated and measured accurately, isotope sample dilution can be achieved by simply monitoring one or a few of the MIRM channels of the analyte in addition to the most abundant MIRM channel for study samples. While the most abundant MIRM channel (isotopic abundance of 100%) is used for the quantitation of samples having concentrations within the assay calibration curve range, less abundant MIRM channels (isotopic abundance of IA%) can be used for the quantitation of samples having concentrations beyond the assay upper limit of quantitation (ULOQ), resulting in isotope dilution factors (IDF) of 100%/IA%. The approaches of one-sample multipoint external calibration curve and isotope sample dilution were evaluated and demonstrated in this work with an example of the quantitation of daclatasvir in human plasma extracted with liquid-liquid extraction. Using these approaches together with the MIRM-ISCC methodology, accurate and reliable LC-MS/MS bioanalysis can be achieved without the need of preparation of multisample external calibration curve and dilution of study samples.