Global metabolomics (G-Met) is a method to simultaneously analyze many endogenous metabolites. It is a valuable tool for identifying disease biomarkers and disease-related pathways. However, obtaining reproducible and reliable G-Met results using liquid chromatography/high-resolution mass spectrometry (LC/HRMS) is challenging. This study aimed to investigate signal drift in continuous plasma LC/HRMS analysis. The LC/HRMS analytical system comprised a TripleTOF 5600 quadrupole timeof-flight hybrid tandem mass spectrometer and a Nexera ultra-high-performance LC system. The analytical column was a Poroshell 120 HILIC-Z PEEK (2.1 mm i.d. × 150 mm, 2.7 μm), with the column oven set at 40°C. Mobile phases A and B consisted of 10 mM ammonium bicarbonate in water/28% aqueous ammonia solution (100:0.1, v/v) and acetonitrile, respectively, and the flow rate was set at 0.3 mL/min. Eight compounds showed MS signal drift, even in the standard analysis. In positive ion mode plasma analysis, an increasing MS signal trend was observed for four compounds. In contrast, six metabolites exhibited a decreasing MS signal in negative ion mode. In particular, during the initial 20 LC/HRMS runs, seven metabolites showed MS signal drifts. In conclusion, stabilization by 20 initial injections and MS signal correction for drift are essential for reliable result of G-Met. We hope that the results of this study will inform future research on plasma G-Met studies.

In the previous paper (Kagaku Kogaku Ronbunshu, 2023, 49, 129-132), we proposed a thermodynamically material-balanced calculation model for chromatograms that allows to being switchable with breakthrough curves according to the injection modes. In terms of numerical analysis, this so-called advection – equilibrium stage model (original model) included an iterative calculation based on a type of explicit solution method (the forward substitution method). We have separately investigated ways to reduce the computational load by aiming to derive a new high-speed computational model using an implicit solution method for sparse matrices. As a result, we proposed a new simplified advection – equilibrium stage model accounting for the advection of solutes between the mobile phase and the stationary phase. This simplified model allows changes to the adsorption isotherm equations, and its application for GC, HPLC or SFC is expected to be expanded for the future.

In our previous study, we found that the combination of large-volume sample stacking with an electroosmotic flow pump (LVSEP) and transient isotachophoresis (tITP), which named large volume dual preconcentration by isotachophoresis and stacking (LDIS), was successfully applied to microchip electrophoresis (MCE). In MCE-LDIS, highly viscous background electrolytes (BGEs) containing sieving polymers such as hydroxypropyl(methyl cellulose) (HPMC) could be employed, which should be effective for concentrating and separating especially for bio-polymeric compounds such as proteins and glycans. To adjust both enrichment efficiencies and resolutions in MCE-LDIS, in this study, the effects of methanol and HPMC additives in the BGE were investigated. In the BGE containing no HPMC, the peak height of a standard dye was increased upon increasing the methanol contents from 0 to 20%, while from 20 to 60% that gradually became smaller. Since the viscosity of water was increased by the addition of 20% methanol from 1.0 to 1.6 cP, the band broadening of the focused analytes would be suppressed, improving the sensitivity enhancement factor (SEF) from 1550 to 8250. Furthermore, the use of the BGE containing both 10% methanol and 1.5% HPMC in LDIS gave the best SEF of 18300 for the standard dye. Addition of methanol and HPMC was also effective for the separation of oligosaccharides, improving the resolutions from 0.85~1.25 to 1.56~1.73. It was revealed that, therefore, methanol and polymer additives were quite important factor for adjusting both SEFs and resolutions in MCE-LDIS.

An isocratic and simple reversed-phase HPLC determination method of cacao polyphenols (CPPs) and methylxanthines in high cacao chocolate was developed with a core-shell (CS) type column and an extraction solvent of a mixture of methanol (MeOH) and acidic water. Simultaneous separation of four major CPPs, namely (-)-epicatechin (EC), (+)-catechin (C), procyanidin B2 and procyanidin C1, and two methylxanthines, caffeine (CAF) and theobromine (TBM) contained in chocolate was successfully performed within ca. 18 min. Among six CS type columns employed, a biphenyl type and a cholesteryl type column gave successful separation. A biphenyl type column, Velox Biphenyl (2.7 m, 4.6 mm × 100 mm) and the mobile phase of a mixture of acetonitrile and 0.1% (v/v) formic acid (10:90, v/v) were used for the assay of chocolate. A mixture of MeOH and 0.1% (v/v) formic acid (70:30, v/v) was effective for the extraction of six components from chocolate matrix, which contains various nutritional components such as fat, protein, sugar etc. More than 90% recoveries for CAF and TMB, and almost 100% recoveries for CPPs were obtained in validation studies. In the developed assay method, EC and CAF were used as the standard substance for six components considering cost limits and simplicity as a quality control method. Other than six components, one unknown peak eluted after CAF in the biphenyl column was identified by LC-MS/MS analysis. As a result, this was found as a fragrance ingredient, vanillin. Assay results by the developed HPLC method gave reasonable content values previously reported. Further determination of vanillin was possible together with assay of these six major components of chocolate.

We have developed a highly sensitive method for the determination of ophthalmic acid (OPH) in human plasma using a derivatization technique with a polyethylene glycol (PEG) reagent combined with hydrophilic interaction liquid chromatography and electrospray ionization-mass spectrometry (HILIC-ESI-MS). In this study, the amino group of OPH was derivatized with a PEG reagent containing an N-hydroxysuccinimide ester to increase the molecular volume of the analyte. The obtained derivative was directly injected into the LC-MS system. Under optimized analytical conditions, PEG-derivatized OPH was successfully retained on the HILIC column, and highly sensitive detection was achieved by negative ESI-MS. The limit of detection was determined to be 0.67 nM (1.67 fmol on column), and the relative standard deviations of the peak areas obtained during intra- and inter-day determinations were within 8.5%. Furthermore, this method can be used to quantify endogenous OPH in pooled human plasma samples.

In recent years, microplastics (MPs) have emerged as a significant environmental concern. The degradation state of MPs in the actual environment varies for each microparticle. For a comprehensive risk assessment of MPs, it is crucial to evaluate diversity at the individual particle level and to analyze measured properties statistically. In this study, we developed capillary size-exclusion chromatography (capillary SEC, inner diameter 0.250 mm × 480 mm) to analyze the molecular weight distribution of MPs at the single-particle level. Additionally, we devised a method for handling single particles to measure samples at the single-particle level using a sampling capillary (inner diameter 0.150 mm × 80 mm). We successfully demonstrated the analysis of a single polystyrene particle with a diameter of 90 μm.

This study focused on the extraction of musty odor compounds, specifically 2-methylisoborneol (2-MIB) and geosmin, from water samples using a thermal desorption (TD) tube packed with a polydimethylsiloxane-coated macroporous silica adsorbent, employing the purge and trap (PT) method. The TD tube was subsequently inserted into a portable TD system, where the extracted compounds were thermally desorbed and introduced into a gas chromatograph-mass spectrometry for analysis. During the PT extraction, the purge gas was flowed at a rate of 200 mL/min for 30 min. Owing to the hydrophobic nature of the PDMS-coated adsorbent, water vapor did not interfere with either the extraction or the desorption processes. The limits of detection and the spike recoveries in tap water samples for 2-MIB and geosmin in a 100 mL water sample were found to be 3.0 and 0.3 ng/L and 108 and 98%, respectively.

Monoacylglycerols (MAGs) are one of the class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. In addition to roles of MAGs as membrane components and energy storages, several MAGs are well-known as a signal mediator. In the present study, authors investigate the mass spectrometry (MS) conditions in the positive ion mode for 10 MAG species to obtain information on sensitivity derived from the combination of the precursor ion and the product ion, and differences in the ionization efficiency of MAG species in liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. Based on studies utilizing a 17:0-MAG standard substance, the combination of an ammonium adduct ion and a dehydroxylated ion showed higher sensitivity compared with other combinations. However, examinations with other MAGs revealed that the slope of the calibration curve varied depending on both the carbon chain length and the desaturation index of acyl groups. Finally, the difference in the calibration slope values was utilized as a correction parameter for the quantification of MAG contents in human lung carcinoma H292 cells to clarify its sensitivity for influenza A virus (IAV) infection. Obtained results suggest that the progression of IAV-infection might disturb intracellular lipid homeostasis, leading to an increase of MAG levels.

Chiral inversion of denopamine (DP, R (-)-form), which is an optically active and an orally administrable cardiotonic agent, was investigated by HPLC with a β-cyclodextrin (β-CD) derivative immobilized chiral column. Enantiomers of DP were successfully separated with a resolution of 2.4 within 10 min under the reversed-phase mode by ULTRON ES-PhCD column, where a perphenylated β-CD derivative was immobilized. Using this chiral HPLC method validated, chiral inversion studies of DP drug substance, DP in tablets and its changed forms (powders and suspensions) under the various stress conditions were performed. As a result, chiral inversion of DP was observed in an aqueous solution state of DP drug substance and suspensions of DP tablets under the heat stress conditions. On the other hand, DP drug substance, DP tablets and its changed forms were stable for heat stress and UV irradiation in the solid state. S (+)-form of DP as a heat degradation product was identified by LC-MS/MS analysis through comparing retention times in chiral HPLC, UV spectra obtained by a photo diode array detector and MS and MS/MS spectra with those of the authentic substance.