Use of ammonium sulfite as a post-column derivatization reagent for rapid detection and quantification of aldehydes by LC-MS

Online coupling of a catalytic continuous microflow reactor to mass spectrometry

Flow cell reactors used for catalyst development and applications are upcoming due to their small environmental and economic footprint. Online microflow reactor coupling with mass spectrometry (MS) opens new possibilities for monitoring catalyst performance and identifying reaction products in real time. This is demonstrated for the metabolic relevant dealkylation of lidocaine on catalytic gold micro-particles using regular liquid chromatography modules. Yields of up to 90% norlidocaine were realized under mild continuous flow conditions for up to 10 h (pH 7, 30 °C and 20 μL/min). Dissolved oxygen was shown to be a rate-limiting factor, since an inline oxygen generator allowed to increase the reactor capacity by one order of magnitude. Monitoring product time-response curve slopes after starting and ending a substrate feed, provided insights into the adsorption/desorption and conversion kinetics at the catalyst surface indicating the presence of strong adsorption sites that do not contribute substantially to substrate conversion.

Developments in on-line, post separation sample manipulation in the last 22 years: Pharmaceutical and biomedical applications

On-line post separation sample manipulation is a powerful approach increasing the sensitivity and selectivity in chemical analysis. Post separation sample manipulation includes the treatment of the analytes after their separation through a suitable separation technique, mainly liquid chromatography and capillary electrophoresis. Typically, post separation approaches include either the addition of a reagent/solvent to derivatize the analyte/enhance the sensitivity, pH change, or the conversion of the analyte through a photochemical/electrochemical system (reagent-free systems). This review focuses on the developed methods using post-column manipulation of sample with pharmaceuticals and biomedical applications, covering the period from 2000 to midle-2023. Chemistries combined with fluorescence, UV-vis and mass spectrometric detection are discussed employing both liquid chromatography and electrophoretic techniques for separation. Noteworthy instrumental modifications are also discussed.

Isotope-coded derivatization with designed Girard-type reagent as charged isobaric mass tags for non-targeted profiling and discovery of natural aldehydes by liquid chromatography-tandem mass spectrometry

Aldehyde-containing metabolites are reactive electrophiles that have attracted extensive attention due to their widespread occurrence in organisms and natural foods. Herein we described a newly-designed Girard's reagent, 1-(4-hydrazinyl-4-oxobutyl)pyridin-1-ium bromide (HBP), as charged tandem mass (MS/MS) tags to facilitate selective capture, sensitive detection and semi-targeted discovery of aldehyde metabolites via hydrazone formation. After HBP labeling, the detection signals of the test aldehydes were increased by 21-2856 times, with the limits of detection were 2.5-7 nM. Upon isotope-coded derivatization with a pair of labeling reagents, HBP-d₀ and its deuterium-labeled counterpart HBP-d₅, the aldehyde analytes were converted to hydrazone derivatives, which generated characteristic neutral fragments of 79 Da and 84 Da, respectively. The isobaric HBP-d₀/HBP-d₅ labeling based LC-MS/MS method was validated by relative quantification of human urinary aldehydes (slope=0.999, R² > 0.99, RSDs ≤ 8.5%) and discrimination analysis between diabetic and control samples. The unique isotopic doubles (Δm/z = 5 Da) by dual neutral loss scanning (dNLS) provided a generic reactivity-based screening strategy that allowed non-targeted profiling and identification of endogenous aldehydes even amidst noisy data. The LC-dNLS-MS/MS screening of cinnamon extracts led to finding 61 possible natural aldehydes and guided discovery of 10 previously undetected congeners in this medicinal plant.

A stability indicating LC-MS/MS method for quantification of a NOX Inhibitor R14 in its bisulfite adduct form for pharmacokinetic studies

R14, also known as NOX Inhibitor VII, is a potent inhibitor of NADPH oxidases (NOX) which has recently been identified as a novel agent targeting to triple-negative breast cancer. It is also rapidly degraded in collected pharmacokinetic plasma and blood samples even stored under - 70 °C. The purpose of this study was to develop a stability indicating LC-MS/MS assay that would be suitable for quantification of R14 in plasma and blood. In the presence of sodium sulfite under acidic pH, R14, an aryl lactam compound which is not a typically reactive compound for bisulfite addition, readily and completely converted to R14 bisulfite adduct, which was more stable in plasma and blood. The adduct has MRM transition at m/z 340.1-127.0 in negative mode and showed high sensitivity in LC-MS/MS quantification. Thus, monitoring the adduct provided a suitable way of quantitating R14 concentrations in mouse whole blood. The reacting conditions were optimized based on detecting R14 bisulfite adduct, and the assay was established and validated on a SCIEX 6500+ Triple Quad LC-MS/MS System. The method was then successfully adapted to pharmacokinetic studies after oral administration of R14 to mice.

Natural cotton fiber-supported liquid extraction for convenient protein-rich aqueous sample preparation: Determination of glucocorticoids in milk and plasma as a proof-of-concept study

Protein-rich aqueous samples such as milk and plasma usually require complex sample preparation steps prior to instrumental analysis. This study proposed a novel cotton fiber-supported liquid extraction (CF-SLE) method for convenient sample preparation. Natural cotton fiber was directly loaded into a syringe tube to conveniently construct the extraction device. No filter frits were required due to the fibrous feature of the cotton fibers. The cost of the extraction device was less than 0.5 CNY, and the costly syringe tube could be easily reused to decrease the cost further. Extraction used a simple two-step protocol: protein-rich aqueous sample loading and elution. Emulsification and centrifugation steps involved in the classic liquid-liquid extraction were avoided. As a proof-of-concept study, the glucocorticoids in milk and plasma were extracted with satisfactory extraction recoveries. Coupled with liquid chromatography-tandem mass spectrometry, a sensitive quantification method was established with excellent linearity (R² > 0.991) as well as good accuracy (85.7-117.3%) and precision (<14.3%). This system is simple, low-cost, reproducible, and easy to automate. Thus, the proposed CF-SLE method is promising for the routine sample preparation of protein-rich aqueous samples prior to instrumental analysis.

The Influence of Intracellular Glutathione Levels on the Induction of Nrf2-Mediated Gene Expression by α-Dicarbonyl Precursors of Advanced Glycation End Products

α-Dicarbonyl compounds, particularly methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG), are highly reactive precursors for the formation of advanced glycation end products (AGEs). They are formed in vivo and during food processing. This study aimed to investigate the role of intracellular glutathione (GSH) levels in the induction of Nrf2-mediated gene expression by α-dicarbonyl compounds. The reactions between α-dicarbonyl compounds (MGO, GO, and 3-DG) and GSH were studied by LC-MS in a cell-free system. It was shown that these three α-dicarbonyl compounds react instantaneously with GSH, with the GSH-mediated scavenging decreasing in the order MGO > GO > 3DG. Furthermore, in a cell-based reporter gene assay MGO, GO, and 3-DG were able to induce Nrf2-mediated gene expression in a dose-dependent manner. Modulation of intracellular GSH levels showed that the cytotoxicity and induction of the Nrf2-mediated pathway by MGO, GO and 3-DG was significantly enhanced by depletion of GSH, while a decrease in Nrf2-activation by MGO and GO but not 3-DG was observed upon an increase of the cellular GSH levels. Our results reveal subtle differences in the role of GSH in protection against the three typical α-dicarbonyl compounds and in their induction of Nrf2-mediated gene expression, and point at a dual biological effect of the α-dicarbonyl compounds, being reactive toxic electrophiles and -as a consequence- able to induce Nrf2-mediated protective gene expression, with MGO being most reactive.

NH2NH-MOF: a reaction matrix for the specific determination of small aldehydes by MALDI-MS

Efficient determination of aldehydes by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is hampered mainly by the low mass and unstable nature of analytes. In the present work, we propose a combined strategy of a reactive metal-organic framework (MOF) matrix for the derivatization and detection of aldehydes. A novel reactive MOF matrix (NH₂NH-MOF) was synthesized in two steps. First, NR₃⁺-MOF was synthesized via Cu²⁺ and the quaternary amine ligand 4,4'-bipyridinium, 1,1″-(1,2-ethanediyl)bis-, dibromide (PyEtBr). Then, -NHNH₂ was introduced to NR₃⁺-MOF through electrostatic adsorption between the -NR₃⁺ and -HSO₃^- of 4-hydrazinylbenzenesulfonic acid to synthesize NH₂NH-MOF. The acid-base chemistry of NH₂NH-MOF led to uniform cocrystallization of the aldehyde-matrix mixtures and helped to achieve the detection of low-weight aldehydes with good relative standard deviations (RSDs = 0.07-12.35%). It was confirmed that this strategy can accurately quantify formaldehyde, valeraldehyde, and benzaldehyde with good linearity (r > 0.97). Furthermore, this strategy was applied to quantitatively detect benzaldehyde in wastewater, thus showing potential applications in environmental pollutant detection.

Progress and Challenges in Quantifying Carbonyl-Metabolomic Phenomes with LC-MS/MS

Carbonyl-containing metabolites widely exist in biological samples and have important physiological functions. Thus, accurate and sensitive quantitative analysis of carbonyl-containing metabolites is crucial to provide insight into metabolic pathways as well as disease mechanisms. Although reversed phase liquid chromatography electrospray ionization mass spectrometry (RPLC-ESI-MS) is widely used due to the powerful separation capability of RPLC and high specificity and sensitivity of MS, but it is often challenging to directly analyze carbonyl-containing metabolites using RPLC-ESI-MS due to the poor ionization efficiency of neutral carbonyl groups in ESI. Modification of carbonyl-containing metabolites by a chemical derivatization strategy can overcome the obstacle of sensitivity; however, it is insufficient to achieve accurate quantification due to instrument drift and matrix effects. The emergence of stable isotope-coded derivatization (ICD) provides a good solution to the problems encountered above. Thus, LC-MS methods that utilize ICD have been applied in metabolomics including quantitative targeted analysis and untargeted profiling analysis. In addition, ICD makes multiplex or multichannel submetabolome analysis possible, which not only reduces instrument running time but also avoids the variation of MS response. In this review, representative derivatization reagents and typical applications in absolute quantification and submetabolome profiling are discussed to highlight the superiority of the ICD strategy for detection of carbonyl-containing metabolites.

Towards Aldehydomics: Untargeted Trapping and Analysis of Reactive Diet-Related Carbonyl Compounds Formed in the Intestinal Lumen

Lipid peroxidation and subsequent formation of toxic aldehydes, such as 4-hydroxynonenal, is known to be involved in numerous pathophysiological processes, possibly including the development of colorectal cancer. This work aimed at the development of an untargeted approach using high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) for tracking aldehydes in both suspect screening and untargeted methods in fecal water, representing the aqueous environment of colon epithelial cells. This original approach is based on the introduction of a characteristic isotopic labeling by selective derivatization of the carbonyl function using a brominated reagent. Following a metabolomics workflow, the developed methodology was applied to the characterization of aldehyde compounds formed by lipid peroxidation in rats fed two different diets differentially prone to lipoperoxidation. Derivatized aldehydes were first selectively detected on the basis of their isotopic pattern, then annotated and finally identified by tandem mass spectrometry. This original approach allowed us to evidence the occurrence of expected aldehydes according to their fatty acid precursors in the diet, and to characterize other aldehydes differentiating the different diets.

[Recent advances in chemical derivatization-based chromatography-mass spectrometry methods for analysis of aldehyde biomarkers]

Human exposure to chemical pollutants in the environment can cause a variety of diseases, including cancer, diabetes, cardiovascular disease, and neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, etc.). Exogenous and environmental pollutant exposure-induced endogenous aldehydes are highly reactive electrophilic compounds that can form covalently modified products with a variety of important biological molecules in the human body, thus inducing toxic effects. Exposome research has become a hotspot since it was first proposed in 2005. Exposure studies can map the complex relationships between biomarkers and disease risk. Therefore, the measurable and characteristic changes of all biomarkers together constitute a key basis for exposome research. Aldehydes are among the main components of chemical exposure. Because of the physical and chemical properties of aldehydes and the existence of multiple matrix interferences in the samples, it is particularly difficult to analyze and characterize them. The analysis and detection methods for aldehydes mainly include sensing analysis, electrochemical methods, fluorescence imaging, chromatography, mass spectrometry (MS), and chromatography-MS. Analytical techniques based on gas chromatography-MS (GC-MS) and liquid chromatography-MS (LC-MS) have emerged as the main methods for chemical exposome research. Chemical derivatization, especially stable isotope labeling derivatization (also known as chemical isotope labeling) combined with LC-MS analytical techniques, can help circumvent the problems encountered in targeted and non-targeted metabolome and exposome analysis. The combination of chemical derivatization with chromatography-MS is one of the most important solutions for the accurate analysis of aldehydes in complex samples. Over the past five years, the development and application of chromatography-MS analytical methods based on chemical derivatization have become key topics in aldehyde analysis. This paper summarizes and reviews the latest progress in GC-MS and LC-MS methods based on chemical derivatization (2015-2020). The review focuses on analytical method development for aldehyde exposure biomarkers in bio-matrices (blood, urine, saliva, biological tissue, etc.). Various derivatization reagents for labeling small-molecule aldehydes, qualitative/quantitative analytical methods and their application value, advantages/disadvantages of different analytical methods for aldehyde exposure biomarkers, and future development trends are also included. The manuscript contents may aid the integrated development of exposome, metabolomics, and lipidomics, as well as research on the environment, ecology, and health. To clarify the complex actions of exogenous and endogenous aldehydes in physiological and pathological events, it is necessary to improve the analysis and characterization techniques and tools for studying the "aldehydome." With the development and application of sophisticated mass spectrometers, advances in high-performance chromatographic separation and bioinformatics, and advent of single-cell analysis and MS imaging, future aldehyde exposome analytical methods will have higher sensitivity and throughput. This in turn would be more useful for screening and identifying unknown aldehyde compounds and discovering new exposome biomarkers.

Microextraction on a screw for determination of trace amounts of hexanal and heptanal as lung cancer biomarkers

Solid phase microextraction on a screw was utilized for the extraction of hexanal and heptanal as lung cancer biomarkers from urine samples. Reduced graphene oxide (rGO) was coated on the surface of a stainless-steel set screw by electrophoretic deposition method. The screw was located inside a glass cover, and the created channel acted as the sample solution flow pass. A 5 mL glass syringe was connected to a syringe pump to direct the sample and the eluent through the channel. The extraction procedure was followed by gas chromatography/mass spectrometry (GC/MS) for separation and determination of the extracted aldehydes. The effective parameters on the extraction efficiencies of the analytes were identified and optimized. Under the optimal extraction conditions, the extraction time was as short as 10 min. The calibration curves indicated good linearity (R² > 0.97) within the concentration range of 1.0-50 μg L^-1. The obtained limits of detection (LODs) for hexanal and heptanal were down to 0.4 and 0.3 μg L^-1, respectively. Considering the repeatability, simplicity, and eco-friendliness of this simple extraction method, it can be efficiently used for preconcentration of aldehydes in different samples.