Abstract: A stir bar sorptive extraction method coupled with deep eutectic solvent based solidification of floating organic droplets-dispersive liquid-liquid microextraction has been used for the simultaneous derivatization and extraction of some acidic pesticides in tomato samples. In this method, initially the analytes are adsorbed on a coated stir bar from tomato juice filled in a narrow tube. After extraction, the stir bar is removed and a water-miscible deep eutectic solvent is used to elute the analytes. Afterward, a derivatization agent and a water-immiscible deep eutectic solvent (as an extraction solvent) with melting point near to room temperature are added to the obtained eluant at µL-levels and the obtained mixture is rapidly injected into deionized water. Under the optimum conditions, the introduced method indicated high enhancement (1543-3353) and enrichment (2530-2999) factors, low limits of detection (7-14 ng/L) and quantification (23-47 ng/L), good linearity (r2 ≥ 0.9982), and satisfactory repeatabilities (relative standard deviation ≤12% for intra- and inter-day precisions at a concentration of 100 ng/L of each analyte). Finally, the proposed method was applied in analysis of the analytes in tomato samples.

Abstract: Plasma-free metanephrines and catecholamines are essential markers in the biochemical diagnosis and follow-up of neuroendocrine tumors and inborn errors of metabolism. However, their low circulating concentrations (in the nanomolar range) and poor fragmentation characteristics hinder facile simultaneous quantification by liquid chromatography and tandem mass spectrometry (LC-MS/MS). Here, we present a sensitive and simple matrix derivatization procedure using propionic anhydride that enables simultaneous quantification of unconjugated l-DOPA, catecholamines, and metanephrines in plasma by LC-MS/MS. Dilution of propionic anhydride 1:4 (v/v) in acetonitrile in combination with 50 μL of plasma resulted in the highest mass spectrometric response. In plasma, derivatization resulted in stable derivatives and increased sensitivity by a factor of 4-30 compared with a previous LC-MS/MS method for measuring plasma metanephrines in our laboratory. Furthermore, propionylation increased specificity, especially for 3-methoxytyramine, by preventing interference from antihypertensive medication (β-blockers). The method was validated according to international guidelines and correlated with a hydrophilic interaction LC-MS/MS method for measuring plasma metanephrines (R2 > 0.99) and high-performance liquid chromatography with an electrochemical detection method for measuring plasma catecholamines (R2 > 0.85). Reference intervals for l-DOPA, catecholamines, and metanephrines in n = 115 healthy individuals were established. Our work shows that analytes in the subnanomolar range in plasma can be derivatized in situ without any preceding sample extraction. The developed method shows improved sensitivity and selectivity over existing methods and enables simultaneous quantification of several classes of amines.

Abstract: Glycosylation is a major protein post-translational modification whose dysregulation has been associated with many diseases. Herein, an on-tissue chemical derivatization strategy based on positively charged hydrazine reagent (Girard's reagent P) coupled with matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) was developed for analysis of N-glycans from FFPE treated tissue sections. The performance of the proposed approach was evaluated by analysis of monosaccharides, oligosaccharides, N-glycans released from glycoproteins, as well as MS imaging of N-glycans from human cancer tissue sections. The results demonstrated that the signal-to-noise ratios for target saccharides were notably improved after chemical derivatization, in which signals were enhanced by 230-fold for glucose and over 28-fold for maltooctaose. Improved glycome coverage was obtained for N-glycans derived from glycoproteins and tissue samples after chemical derivatization. Furthermore, on-tissue derivatization was applied for MALDI-MSI of N-glycans from human laryngeal cancer and ovarian cancer tissues. Differentially expressed N-glycans among the tumor region, adjacent normal tissue region, and tumor proximal collagen stroma region were imaged, revealing that high-mannose type N-glycans were predominantly expressed in the tumor region. Overall, our results indicate that the on-tissue labeling strategy coupled with MALDI-MSI shows great potential to spatially characterize N-glycan expression within heterogeneous tissue samples with enhanced sensitivity. This study provides a promising approach to better understand the pathogenesis of cancer related aberrant glycosylation, which is beneficial to the design of improved clinical diagnosis and therapeutic strategies.

Abstract: Sustainable biopolymers are promising raw resources for the development of novel biomaterials with vast potential in various application fields. Nonetheless, the processing and derivatization of bi...

Abstract: Carboxyl-containing metabolites (CCMs) play indispensable roles in cell energy metabolism and cell-cell signaling. Profiling tissue CCMs with spatial signatures is significant for the understanding of molecular histology and may provide new clues to uncover the complex metabolic reprogramming of organisms in response to external or internal stimuli. Here, we develop a sensitive on-tissue CCMs derivatization method, coupled with matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI), to visualize the spatial distributions of CCMs in biological tissues. A novel reagent, N,N,N-trimethyl-2-(piperazin-1-yl)ethan-1-aminium iodide (TMPA), was synthesized and used for the on-tissue derivatization of CCMs. Meanwhile, the on-tissue derivatization efficiency was significantly improved by introducing acetonitrile gas in the incubation system. With this methodology, a total of 28 CCMs, including 5 tricarboxylic acid cycle intermediates, 20 fatty acids, and 3 bile acids, were successfully detected and imaged in rat kidney tissues. More importantly, the introduction of a quaternary ammonium group into the chemical structure of CCMs enables simultaneous MALDI-MS imaging of tricarboxylic acid cycle intermediates, fatty acids, bile acids, and their metabolic pathway-related metabolites such as carnitines, cholines, glycerophosphocholine, phospholipids, and so on in the positive ion mode. This on-tissue derivatization MALDI-MSI approach was proven to be a powerful tool for probing the distributions and spatial metabolic networks of CMMs in biological tissues.

Abstract: In this work, we developed a rapid and high-sensitivity method for simultaneous analyses of fatty alcohols, fatty aldehydes, and sterols by combining the optimized derivatization reaction with electrospray ionization-ion mobility-mass spectrometry (ESI-IM-MS). Pyridine and thionyl chloride were used as derivatization reagents as they were easily removed after the derivatization reaction and could generate permanently charged tags on different functional groups including hydroxyls and aldehydes. Through this one-step derivatization reaction, the sensitivity of detection for fatty alcohols, fatty aldehydes, and sterols was significantly increased. Moreover, the introduction of ion mobility spectrometry (IMS), offering an additional resolution power, ensured more sensitive and accurate detection of derivative products without increasing analytical time. Being connected with high-performance liquid chromatography, more than 15 kinds of compounds were analyzed within 4 min. Relative quantification using peak intensity ratios between d0-/d5-labeled ions were subsequently applied for analyzing these 15 kinds of compounds in human thyroid carcinoma and para-carcinoma tissues. The results showed significant differences in content of some analytes between these two kinds of tissues (p < 0.05). The correlations between most of the analytes in thyroid carcinoma tissues are better than the correlations in para-carcinoma tissues.

Abstract: Histamine level determination in fish and fish products is important for human safety, fish quality and food industry. For this reason, a rapid, robust, and precise method is needed. To achieve this objective, an HPLC method with fluorescence detection was developed and validated. Histamine in fish samples was efficiently extracted with perchloric acid, and purified with ion-exchange solid-phase extraction cartridge. A pre-column derivatization was adopted with ortho-phthalaldehyde (OPA) in the presence of the reducing agent 2-mercaptoethanol, and the stability of the histamine-OPA derivatives was achieved with the acidification of the reaction medium. In terms of validation, besides the excellent linear correlations, satisfactory recoveries at all spiking levels ranging between 0 and 200 mg kg−1 were attained, with limit of detection calculated at 1.8 mg kg−1, whereas limit of quantification determined at 5 mg kg−1. The proposed method was successfully used in the analysis of reference materials and proficiency tests, and was found to be suitable, accurate, and rapid for detection and quantification of histamine in various fish samples.

Abstract: A chemical-derivatization-triggered aggregation-induced emission (AIE) method for the highly selective determination of hydrogen sulfide (H2S) in wine matrices by high-performance liquid chromatography with fluorescence detection (HPLC-FLD) was developed. The detection strategy was developed based on the chemical derivatization of H2S using a low-cost AIE-active fluorescence derivatization reagent, N-(3-iodine-2-oxopropyl)pyrene methamine (NIPM), to trigger specific AIE at 475 nm, which was red-shifted sharply to the maximum emission wavelength as compared with NIPM monomers of 375 nm, effectively quenching the interference from other thiol-containing compounds. With the aid of specific AIE and the effective separation of HPLC, the proposed method showed high selectivity and sensitivity toward H2S. The limits of detection (LODs) at the sub-nM level of 0.25 nmol/L in the wine-beer sample and 0.30 nmol/L in red wine sample were obtained. To certify its applicability, this proposed strategy was successfully applied for the determination of H2S in wine matrices.

Abstract: Monitoring of biogenic amines in food is important for quality control, in terms of freshness evaluation and even more for food safety. A novel and cost-effective method was developed and validated for the determination of the main biogenic amines: histamine, putrescine, cadaverine, spermidine and spermine in fish tissues. The method includes extraction of amines with perchloric acid, pre-column derivatization with Pyrene Sulfonyl Chloride (PSCl), extraction of derivatives with toluene, back-dissolution in ACN after evaporation and determination by reversed phase high performance liquid chromatography with UV and intramolecular excimer fluorescence detection. The structure of the pyrene-derivatives was confirmed by liquid chromatography-mass spectrometry with electrospray ionization. The standard addition technique was applied for the quantitation due to significant matrix effect, while the use of 1,7-diaminoheptane as internal standard offered an additional confirmation tool for the identification of the analytes. Method repeatability expressed as %RSD ranged between 7.4-14% for the different amines and recovery ranged from 67% for histamine up to 114% for spermine. The limits of detection ranged between 0.1-1.4 mg kg-1 and the limits of quantification between 0.3-4.2 mg kg-1. The method was applied to canned fish samples and the concentrations of the individual biogenic amines were below the detection limit up to 40.1 mg kg-1, while their sum was within the range 4.1-49.6 mg kg-1.

Abstract: Mapping the complete molecular composition of a lipidome is considered an important goal of lipidomics for unraveling pathways and mechanisms behind lipid homeostasis. Conventional dissociation methods of mass spectrometry (MS) usually cannot give detailed structural information on lipids such as locations of carbon-carbon double bonds (C═C) in acyl chains. Double-bond derivatization via the Paterno-Buchi (PB) reaction has been demonstrated as a simple and highly efficient method for identification of C═C locations of different classes of lipids when paired with tandem mass spectrometry (MS/MS). In this work, reversed-phase lipid chromatography (RPLC)-MS was coupled with an online PB reaction to achieve enhanced analysis of isomers and isobars of phospholipids. A new acetone-containing mobile phase was developed that showed good elution performance for the separation of phospholipids by C18 columns. An improved flow microreactor was developed, enabling online derivatization of phospholipid C═C in 20 s. The workflow of RPLC-PB-MS/MS was developed and optimized for identification of C═C locations in isobaric ether-linked and diacyl phospholipids, 13C isobars, and acyl chain isomers in biological lipid extracts. Separation and identification of C═C locations of cis/trans phospholipid isomers were achieved for lipid standards. The incorporation of the PB reaction into the RPLC-MS workflow enabled analysis of phospholipid isomers and isobars with high confidence, demonstrating its potential for high-throughput phospholipid identification from complex mixtures.

Abstract: An antimalarial lipopeptide, ikoamide, was isolated from an Okeania sp. marine cyanobacterium. Its gross structure was established by spectroscopic analyses, and the absolute configuration was clarified based on a combination of chiral-phase HPLC analyses, spectroscopic analyses, and derivatization reactions. Ikoamide showed strong antimalarial activity with an IC50 value of 0.14 μM without cytotoxicity against human cancer cell lines at 10 μM.

Abstract: Sample pretreatment is the first and the most important step of an analytical procedure. In routine analysis, liquid–liquid microextraction (LLE) is the most widely used sample pre-treatment techni...

Abstract: Short-chain fatty acids (SCFAs) were identified as critical markers in the diagnosis of chronic and metabolic diseases, but a sensitive and stable method to determine SCFAs in feces is a challenge for analysts due to the high volatility. Herein, a sensitive and accurate method to determine SCFAs adopting precolumn derivatization coupled with gas chromatography-mass spectrometry (GC-MS) has been developed. Benzyl chloroformate (BCF) was chosen as the reaction reagent and emulsified derivatization was applied to homogenize the reaction system. Higher sensitivity, wider application and satisfactory derivatization efficiency were obtained using the developed method. An excellent method validation showed a good linearity ranging from 0.9947 to 0.9998. At the same time, the intra-day and inter-day precision were achieved in the range of 0.56% to 13.07%. The lower limits of detection of all target analytes varied from 0.1 to 5 pg. The recovery ranged from 80.87% to 119.03%, and storage stability under three different conditions was also determined. This method was also successfully applied to the analysis of SCFAs in mice fecal samples to illustrate the significant differences between normal and type 2 diabetes mellitus mice.

Abstract: Determination of the L- and D-amino acid composition in proteins is important for monitoring process-induced racemization, and thereby protein quality loss, in food and feed. Such analysis has so far been challenging due to the need for sample hydrolysis, which generates racemization, thereby leading to an overestimation of D-amino acids. Here, validation of an LC-MS/MS-based method for the simultaneous determination of L- and D-amino acids in complex biological matrixes, like food and feed, was performed in combination with deuterated HCl hydrolysis. This approach eliminated a racemization-induced bias in the L- and D-amino acid ratios. The LC-MS/MS method was applied for the analysis of 18 free amino acids, with a quantification limit of either 12.5 or 62 ng/mL, except for D-phenylalanine, for which quantification was impaired by background interference from the derivatization agent. For hydrolyzed samples, the composition of 10 L- and D-amino acids pairs could be determined in protein. The average relative standard deviation was 5.5% and 6.1%, depending on the type of hydrolysis tubes. The method was applied on a green protein isolate (lucerne), which contained an average of 0.3% D-amino acids. In conclusion, this method allows for an unbiased analysis of L- and D-amino acid ratios in complex protein samples, such as food and feed.

Abstract: For single living cell mass spectrometry measurement, sensitivity is of great significance due to the extremely complicated chemical components of the cytoplasm. Higher sensitivity is always highly desired, especially for chemicals with low concentrations or poor mass spectrometry responses. Here, a quaternary ammonium salt group-based charge tag was designed to enhance the analytical performance for cysteine within single cells using induced nanoelectrospray mass spectrometry. While the charge tag was coupled to the analyte via biocompatible click reaction, viability of the living cells was maintained during in situ derivatization and following analysis. Enhanced sensitivity under physiological conditions for cysteine, at pH 7.4 and with highly concentrated salts, was achieved due to higher ionization efficiency of the charge tag. Therefore, the cysteine levels in single living HeLa cells and HepG2 cells were found to be in the range of 62.0 ± 3.4 μM and 49.6 ± 7.2 μM, respectively. Furthermore, the low cysteine levels in living single HeLa cells could be monitored, in the presence of cystine transporter inhibitor. Thus, this method provides a general strategy for in situ chemical derivatization for signal amplification in the field of single cell mass spectrometry.