Comparison of LC-MS3 and LC-MRM strategy for quantification of methotrexate in human plasma and its application in therapeutic drug monitoring

Mass spectrometry analysis of phosphotyrosine-containing proteins

Tyrosine phosphorylation is a crucial posttranslational modification that is involved in various aspects of cell biology and often has functions in cancers. It is necessary not only to identify the specific phosphorylation sites but also to quantify their phosphorylation levels under specific pathophysiological conditions. Because of its high sensitivity and accuracy, mass spectrometry (MS) has been widely used to identify endogenous and synthetic phosphotyrosine proteins/peptides across a range of biological systems. However, phosphotyrosine-containing proteins occur in extremely low abundance and they degrade easily, severely challenging the application of MS. This review highlights the advances in both quantitative analysis procedures and enrichment approaches to tyrosine phosphorylation before MS analysis and reviews the differences among phosphorylation, sulfation, and nitration of tyrosine residues in proteins. In-depth insights into tyrosine phosphorylation in a wide variety of biological systems will offer a deep understanding of how signal transduction regulates cellular physiology and the development of tyrosine phosphorylation-related drugs as cancer therapeutics.

LC-MS-MS-MS3 for the determination and quantification of ∆9-tetrahydrocannabinol and metabolites in blood samples

Due to the high prevalence of cannabinoids in forensic toxicology analysis, it is crucial to have an efficient method that allows the use of a small sample amount and that requires a minimal sample preparation for the determination and quantification of low concentrations. A simple, highly selective and high throughput liquid chromatography-tandem mass spectrometry methodology (LC-MS-MS-MS3) was developed for the determination and quantification of ∆9-tetrahydrocannabinol (THC), 11-hydroxy-∆9- tetrahydrocannabinol (THC-OH) and 11-nor-9-carboxy-∆9-tetrahydrocannabinol (THC-COOH) in blood samples. Chromatographic analysis of THC, THC-OH and THC-COOH and their deuterated internal standards was preceded by protein precipitation (PPT) of 0.1 mL of blood samples with acetonitrile. Chromatographic separation was achieved by use of an Acquity UPLC® HHS T3 (100 mm × 2.1 mm i.d., 1.8 μm) reversed-phase column, using a gradient elution of 2 mM aqueous ammonium formate, 0.1% formic acid and methanol at a flow rate of 0.4 mL/min, with a run time of 10 min. For the MS-MS-MS3 analysis, a SCIEX QTRAP® 6500+ triple quadrupole linear ion trap mass spectrometer was used via electrospray ionization (ESI), operated in multiple reaction monitoring (MRM) and linear ion trap mode (MS3). The method was validated in accordance with internationally accepted criteria and guidelines, and proved to be selective and linear between 0.5 and 100 ng/mL (r2 > 0.995). The lower limits of quantification (LLOQ) corresponded to the lowest concentrations used for the calibration curves. The coefficients of variation obtained for accuracy and precision were <15%. The mean recoveries were between 88.0% and 117.2% for the studied concentration levels (1 ng/mL, 5 ng/mL and 50 ng/mL). No significant interfering compounds, matrix effects or carryover were observed. The validated method provides a sensitive, efficient and robust procedure for the quantification of cannabinoids in blood, using LC-MS-MS-MS3 and a sample volume of 0.1 mL. This work is also a proof of concept for using LC-MS3 technique to determine drugs in biological samples.

Comparison of LC-MS3 and LC-MRM Method for Quantifying Voriconazole and Its Application in Therapeutic Drug Monitoring of Human Plasma

The TDM of voriconazole which exhibits wide inter-individual variability is indispensable for treatment in clinic. In this study, a method that high-performance liquid chromatography tandem mass spectrometry cubed (HPLC-MS3) is first built and validated to quantify voriconazole in human plasma. The system is composed of Shimadzu Exion LCTM UPLC coupled with a Qtrap 5500 mass spectrometer. The separation of voriconazole is performed on a Poroshell 120 SB-C18 column at a flow rate of 0.8 mL/min remaining 7 min for each sample. The calibration curves are linear in the concentration range of 0.25–20 μg/mL. Intra-day and inter-day accuracies and precisions are within 8.0% at three concentrations, and the recoveries and matrix effect are all within accepted limits. In terms of stability, there is no significant degradation of voriconazole under various conditions. The HPLC-MS3 and HPLC-MRM (multiple reaction monitoring) methods are compared in 42 patients with Passing–Bablok regression and Bland–Altman plots, and the results show no significant difference between the two methods. However, HPLC-MS3 has a higher S/N (signal-to-noise ratio) and response than the MRM. Finally, the HPLC-MS3 assay is successfully applied to monitor the TDM (therapeutic drug monitoring) of voriconazole in human plasma, and this verifies that the dosing guidelines for voriconazole have been well implemented in the clinic and patients have received excellent treatment.

Evaluation of multiple reaction monitoring cubed performed by a quadrupole-linear ion trap mass spectrometer for quantitative determination of 6-sulfatoxymelatonin in urine

Liquid chromatography (LC) - mass spectrometry quantitative analysis of substances in biological samples is usually performed in the multiple reaction monitoring (MRM) variant. In complex biological matrices, strong interferences can be observed when using the LC-MRM method. Interference levels can be significantly reduced by using LC - multiple reaction monitoring cubed (MRM³). 6-sulfatoxymelatonin (6-SM) is a metabolite of melatonin, an important regulator of many biological processes. The quantitative analysis of 6-SM in urine allows monitoring of the melatonin level in the blood. The aim of the present work was to evaluate the LC-MRM³ method for the quantitative determination of 6-SM in urine. We found that for 6-SM in aqueous solutions, under some parameters of the MRM³ experiment, the effect of degradation of the MRM³ signal is observed. When analyzing 6-SM in urine, this signal degradation effect was significantly reduced. We have shown that optimization of such parameters of the MRM³ method as the linear ion trap fill time, the number of scans to sum, and the range of triple-stage scan allows obtaining the LC-MRM³ method, which is comparable to the LC-MRM in sensitivity and significantly exceeds it in selectivity.

Towards Higher Sensitivity of Mass Spectrometry: A Perspective From the Mass Analyzers

Mass spectrometry (MS) is one of the most widely used analytical techniques in many fields. Recent developments in chemical and biological researches have drawn much attention to the measurement of substances with low abundances in samples. Continuous efforts have been made consequently to further improve the sensitivity of MS. Modifications on the mass analyzers of mass spectrometers offer a direct, universal and practical way to obtain higher sensitivity. This review provides a comprehensive overview of the latest developments in mass analyzers for the improvement of mass spectrometers' sensitivity, including quadrupole, ion trap, time-of-flight (TOF) and Fourier transform ion cyclotron (FT-ICR), as well as different combinations of these mass analyzers. The advantages and limitations of different mass analyzers and their combinations are compared and discussed. This review provides guidance to the selection of suitable mass spectrometers in chemical and biological analytical applications. It is also beneficial to the development of novel mass spectrometers.