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Nanospray desorption electrospray ionization (nano-DESI) is one of the ambient desorption ionization methods for mass spectrometry (MS), and it utilizes a steady-state liquid junction formed between two microcapillaries to directly extract analytes from sample surfaces with minimal sample damage. In this study, we employed nano-DESI MS to perform a metabolite fingerprinting analysis directly from a Hypericum leaf surface. Moreover, we investigated whether changes in metabolite fingerprints with time can be related to metabolite distribution according to depth. From a raw Hypericum leaf, the mass spectral fingerprints of key metabolites, including flavonoids and prenylated phloroglucinols, were successfully obtained using ethanol as a nano-DESI solvent, and the changes in their intensities were observed with time via full mass scan experiments. In addition, the differential extraction patterns of the obtained mass spectral fingerprints were clearly visualized over time through selected ion monitoring and pseudo-selected reaction monitoring experiments. To examine the correlation between the time-dependent changes in the metabolite fingerprints and depth-wise metabolite distribution, we performed a nano-DESI MS analysis against leaves whose surface layers were removed multiple times by forming polymeric gum Arabic films on their surfaces, followed by detaching. The preliminary results showed that the changes in the metabolite fingerprints according to the number of peelings showed a similar pattern with those obtained from the raw leaves over time. [ABSTRACT FROM AUTHOR]

Reactive ionization with atmospheric pressure ionization (API) methods have been utilized for mass spectrometry (MS) to enhance ionization efficiency of an analyte, to recognize a specific functional group of an analyte, and to investigate reaction pathways or intermediates for a certain in situ reaction. Paper spray ionization (PSI) is one of the major API techniques for reactive ionization. In reactive PSI, one of the reactants is usually spotted onto a paper tip and the other reactant is delivered through a spraying solution. After in situ reaction, reaction products are transported to the end of the tip and ionized. In this study, we investigated reactions between isothiazolinones (ITs) and cysteamine (CA) by reactive PSI MS. An IT is a heterocyclic compound that has a conjugated ketone moiety and used as a biocide or a preservative. CA is a stable aminothiol that is often used as a bifunctional covalent modifier. Through reactive PSI MS of ITs with CA, we found that a covalent modification of an IT by CA was possible and sensitivities for ITs were improved compared to conventional PSI MS of ITs that did not employ CA. In addition, possible reaction pathways between ITs and CA during reactive PSI were suggested although we could not confirm a specific reaction pathway in the current study. [ABSTRACT FROM AUTHOR]

Citrullination is a post‐translational modification that converts arginine into citrulline through deimination. As citrullination is accompanied by only about 1 Da increase in mass, ion signals of a citrullinated peptide in a mass spectrum are always overlapped with the isotope peaks of its control (a noncitrullinated form). Therefore, off‐line, covalent labeling techniques on citrulline residues were usually employed to investigate citrullinated sites by mass spectrometry (MS). Recently, reactive desorption electrospray ionization (reactive DESI) MS was introduced as a tool for selective, in situ modification of target analytes. In reactive DESI MS, a chemical reagent that can readily react with a target analyte is sprayed onto a sample spot and resulting products are analyzed by MS. Here, we developed a reactive DESI MS method for determining the citrullinated sites in peptides by employing phenylglyoxal as a derivatization agent, and succeeded in selectively modifying a citrulline residue in a peptide. [ABSTRACT FROM AUTHOR]

We developed a modified paper spray ionization (PSI) platform, named as paper cone spray ionization (PCSI), for direct mass spectrometric analysis of raw solid samples. The major modification from conventional PSI was the geometry of the paper base: PCSI uses a triangular-pyramidal-shaped paper tip instead of a planar triangular-shaped one. This three-dimensional paper cone serves as a sample container, an in situ solid–liquid extraction chamber, an analyte transport channel, as well as an electrospray tip. Unlike conventional PSI mass spectrometry (MS), a weighing paper with relatively low permeability was found to be more suitable for PCSI MS than other papers. PCSI MS rapidly generated major chemical fingerprints from various solid materials including powdered tablets as well as raw and processed food materials without any sample pre-treatment. [ABSTRACT FROM AUTHOR]

In this note, we report that high quality ganglioside profiles with minimal loss of sialic acid residues can be obtained in the positive ion mode by using a 5-methoxysalicylic acid (MSA) matrix for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Our results showed that MSA produced much less sialic acid losses from gangliosides than DHB, although MSA and DHB are differ only by their functional groups at their 5-positions (-OH for DHB and -OCH for MSA). Furthermore, our data also demonstrated that addition of an alkali metal additive was effective for simplifying ganglioside profiles, but not necessary for stabilizing glycosidic bonds of gangliosides if MSA was used as a matrix. This suggests that MALDI MS with MSA has a potential to gain additional benefits from the positive-ion mode analyses without losing performance in ganglioside profiling. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This paper reviews the application of ambient desorption/ionization (ADI) mass spectrometry (MS) to the direct analysis of solid materials. First, ADI methods are introduced according to the sampling and desorption processes, including liquid extraction, plasma desorption, thermal desorption, and laser ablation/desorption, along with their practical features and limitations in the direct analysis of solid objects. Various cases of real-world analysis are also summarized: analysis of active compounds in pharmaceuticals and herbal medicines; analysis of food products for quality control and origin tracking; forensic analysis for sexual assault crimes, explosives, and illicit drug abuse; and surface contaminant analysis for food and environmental safety control. An overview of relevant discussions shows that ADI-MS techniques allow the direct desorption and ionization of analytes from untreated samples under ambient conditions, resulting in tremendous improvements in efficiency in speed and procedural simplicity. • Ambient desorption/ionization (ADI) methods enable fast direct MS analysis of solid materials with minimal sample preparation. • Features and limitations of each ionization technique in direct solid material analysis are discussed. • Applications in pharmaceutical, food, herbal, forensic, and environmental analyses are presented. [ABSTRACT FROM AUTHOR]

Sulfite, a widely used food additive, is subject to regulated labeling. The extraction of sulfite as the stable hydroxymethylsulfonate (HMS) form and its quantitative analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been recognized for their good sensitivity, selectivity, and versatility across various food materials. This study aimed to develop a cost-effective and simpler method for sulfite quantitation, while maintaining the superior sensitivity and selectivity of mass spectrometry (MS). To achieve this, we introduced paper spray ionization (PSI), an ambient desorption ionization technique that could achieve the direct measurement of analytes without employing separation. We also employed a novel internal standard (IS) structurally similar to the analyte, replacing the more expensive isotopically labeled IS. Although the PSI-MS/MS method developed in this study exhibited slightly lower analytical performance compared to the conventional LC-MS/MS, it remained effective for sulfite analysis in dried fruits. [ABSTRACT FROM AUTHOR]

Paper spray ionization (PSI) is an extractive ambient ionization technique for mass spectrometry (MS), whereby a triangular paper tip serves as the sampling base and the electrospray tip. During PSI, analytes are extracted and transported to the edge of the paper tip by the applied spraying solvent. Analytes can be purified from a sample matrix and separated from each other by this transportation process. In this study, we investigated and utilized the analyte transportation process of PSI for the in situ separation and analysis of lipid mixtures. We found that differential transport of phosphatidylcholine (PC) and triacylglycerol (TAG), the two most abundant lipid classes in animals, occurred during PSI. We also found that the order in which these lipids moved strongly depended on how the spraying solvent was applied to the paper base. The more polar PC moved faster than the less polar TAG during PSI, when a polar solvent was slowly fed into a paper tip, whereas TAG was transported faster than PC when excess solvent was applied to the tip at once. In addition, we achieved a complete separation and detection of PC and TAG by slowly supplying a nonpolar solvent to a PSI tip. [ABSTRACT FROM AUTHOR]

Gangliosides are amphiphilic, acidic glycosphingolipids possessing one or more sialic acid residues and several isobaric structural isomers with different abundances and bioactivities. Therefore, the distinction between these isomers is crucial for their proper profiling. Although liquid chromatography–mass spectrometry has been successfully employed for this purpose, the distinction process can still be improved, particularly regarding liquid chromatography. Recently, a reversed‐phase liquid chromatography method that could separate disialoganglioside isomers was reported; however, the distinction of trisialoganglioside isomers using reversed‐phase liquid chromatography has not been demonstrated. Here, we investigated the practicality of a reversed‐phase liquid chromatography with an octadecylsilane column for separating polysialoganglioside isomers and successfully achieved the isomer separation of disialogangliosides and trisialogangliosides for the first time. We also confirmed several crucial factors in the mobile‐phase composition, which affect the differential retention and mass spectral response of the isomers. First, an organic modifier, acetonitrile, exhibited superior selectivity against polysialogangliosides over methanol. Second, ammonium bicarbonate was the best ammonium salt additive among those tested, in terms of the separation efficiency and mass spectral response. Third, as the ammonium salt concentration increased, the negative electrospray ionization response was extensively suppressed, and the retention of gangliosides increased. [ABSTRACT FROM AUTHOR]

Paper spray ionization mass spectrometry (PSI MS) has emerged as a notable method for the rapid analysis of biological samples. However, the typical cellulose-based paper tip is incompatible with protein detection due to the strong interaction between cellulose hydroxyl groups and proteins. In this study, we utilized a commercially available polyolefin-based synthetic paper, Teslin®, as an alternative PSI substrate for simple protein analysis. We have named this method "droplet PSI" MS, as the aqueous protein solution droplet retains its shape on the Teslin® paper tip. For droplet PSI, no further chemical pretreatment was necessary for the Teslin® substrate; the only required preparation was shaping the Teslin® paper into a triangular tip. In droplet PSI MS, protein ion signals were instantly detected from a protein solution droplet upon applying a spray solvent in situ along with high voltage (HV). When compared with conventional PSI MS, our method demonstrated superior sensitivity. The droplet PSI MS utilizing Teslin® also showcased flexibility in real-time observation of protein alterations induced by an acid additive. Additionally, the effects of spray solvent composition and the application method were discussed. [ABSTRACT FROM AUTHOR]

Arginine residues in a protein can be enzymatically deiminated to citrulline residues, and this post-translational modification of proteins, called citrullination, has been known to be associated with autoimmune diseases such as rheumatoid arthritis. Since citrullination of an arginine residue causes a mass shift of only 1 Da, isotopic distribution patterns of citrullinated and its control (non-citrullinated) peptides overlap each other, and the resulting isotopic pattern is skewed with respect to that of the control peptide. Recently, Deforce and coworkers utilized the citrullination-induced skewed isotopic patterns for estimating the extent of citrullination ( J. Proteome Res. 2012, 11, 5245). However, electrospray ionization ( ESI), which Deforce and coworkers employed, is not fully suitable for this type of quantification because the number of potential charge sites on a citrullinated peptide is less than that on its control peptide and this leads to different ion abundances for a given charge state. In this study, we employed matrix-assisted laser desorption/ionization ( MALDI) instead of ESI for quantification of citrullination because the preference for singly charged ion formation by MALDI may overcome the aforementioned issue. Our results show that the isotopic patterns generated by MALDI time-of-flight ( TOF) mass spectrometry ( MS) reflect the citrullination contents better than those generated by ESI linear ion trap ( LIT) MS. [ABSTRACT FROM AUTHOR]

Paper cone spray ionization ( PCSI), an extractive ambient ionization method that is specialized for raw solid material analysis, was applied to chemical fingerprinting analysis of raw medicinal herbs. Experimental parameters of PCSI mass spectrometry ( MS) were first optimized against Salvia miltiorrhiza Bunge (danshen). Our results showed that simple alkyl alcohols, such as methanol and 2-propanol, generally worked well in both polarities and could generate representative chemical fingerprints instantly for a given herbal sample. In addition, in situ extraction from untreated herbal slices during PCSI MS was found to be enough to generate characteristic chemical signatures of a given medicinal herb. After optimization, representative fingerprints of various medicinal herbs, including Sophora flavescens (kushen) and Paeonia lactiflora Pall (shaoyao), were successfully obtained by PCSI MS. In addition, morphologically similar herbs, Cynanchum auriculatum and Cynanchum wilfordii, could be differentiated from each other by their chemical signatures by PCSI MS. [ABSTRACT FROM AUTHOR]

Triacylglycerols (TAGs), essential energy storage lipids, are easily detected by conventional MALDI MS when occurring on their own. However, their signals are easily overwhelmed by other lipids, mainly phosphatidylcholines (PCs) and, therefore, require purification. In order to profile TAGs from crude lipid mixtures without prefractionation, we investigated alternative matrixes that can suppress phospholipid ion signals and enhance cationization of TAGs. We found that an aqueous solution of citrate-capped gold nanoparticles (AuNPs) with a diameter of 12 nm is a superior matrix for the laser desorption/ionization mass spectrometry (LDI MS) of TAGs in crude lipid mixtures. The AuNP matrix effectively suppressed other lipid signals such as phospholipids and also provided 100 times lower detection limit for TAGs than 2,5-dihydroxybenzoic acid (DHB), the best conventional MALDI matrix for TAGs. The AuNP-assisted LDI MS enabled us to obtain detailed TAG profiles including minor species directly from crude beef lipid extracts without phospholipid interference. In addition, we could detect TAGs at a trace level from a total brain lipid extract. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Paper spray chemical ionization (PSCI) combined with mass spectrometry has been proposed as a sensitive method for the analysis of nonpolar aromatic compounds; however, the mechanism behind PSCI is not well understood. In the present study, the evidence for the occurrence of corona discharge is provided and its mechanism is proposed. Photographs taken with a highly sensitive camera evidently demonstrate the occurrence of corona discharge at the end of the triangular shape tip when a nonpolar solvent such as hexane was used at an applied potential of 6–7 kV. Nevertheless, corona discharge was not observed in the presence of a polar solvent. The occurrence of the corona discharge was attributed to charge accumulation in the dielectric layer generated by the nonpolar solvent on the fibers of the paper tip. Specifically, corona discharge was generated at the tip end when the charge approached a critical threshold. In the presence of a polar solvent, however, the dielectric layer was not generated and, hence, corona discharge was not observed. Based on this information, three nonpolar solvents were selected and their sensitivity for analyzing the phenanthrene and maltene fractions of crude oil was evaluated. Chlorobenzene provided the highest signal abundance; therefore, it was suggested as the optimum solvent for PSCI. Notably, the fundamental understanding of corona discharge in PSCI acquired in this study provides a basis for further improvement of this technique by way of surface modification. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • First application of PSI-MS on photodegraded and degraded spilled oil samples. • PSI-MS is shown to be a suitable technique for spilled oil analysis. • Parameter derived from PSI-MS spectra to estimate the degree of degradation of oils. Abstract Paper spray ionization mass spectrometry (PSI-MS) was applied for the first time to study temporal change of photo-oxidized and weathered oils subjected to degradation. PSI is chosen in this study because it is an optimal ionization technique for the analysis of degraded oils with limited sample quantity and prone to salt and particulate contamination. With PSI-MS, quantitative analysis of oils can be successfully performed with as little as 2 μg of oil sample. In addition, oil solutions containing up to 0.05% sodium chloride were successfully analyzed with PSI-MS. In the PSI-MS spectra of photo-degraded oils, the relative abundance of compounds having double equivalence value (DBE) ≥ 5 increased but those with DBE < 5 decreased in number. The summed abundance ratio of compounds having DBE < 5 and DBE ≥ 5 showed a negative exponential correlation with the duration of UV exposure in laboratory experiments. The same trend was observed from spilled oils obtained from the environment. Therefore, this ratio serves as an effective means to estimate the degree of weathering in spilled oils. [ABSTRACT FROM AUTHOR]

Antibiotics in environment can be of concern as they can enter the food chain posing risks to ecosystems and human health. Photodegradation has been considered as a promising way of naturally degrading antibiotics in environment. Antibiotics are usually present in mixtures in environment; however, previous studies focused on individual compounds. Therefore, this study investigated the effect of UV irradiation on the degradation of tetracycline (TC) and sulfathiazole (STH) in individual solutions and mixtures. Under dark conditions, the initial masses of TC and STH were reduced by about 35% and 26%, respectively, over a 35 d-reaction period. With UV irradiation TC and STH were completely removed within 14 d and 35 d, respectively, regardless of the initial concentrations. Both the TC and STH removals were faster (i.e., 2–4 times) when they were in mixtures. This may be partly attributed to the byproducts such as sulfate that can promote indirect photolysis and partly to the enhanced hydrolysis due to changes in the solution pH. Overall, this study suggests that when photodegradation is used to remove antibiotics in water, the removal kinetics of antibiotics individually and in mixtures can be considered to develop more efficient treatment technologies. [ABSTRACT FROM AUTHOR]

Phenols are significant environmental endocrine disruptors that can have adverse health effects on exposed individuals. Correlating phenol exposure to potential health implications requires the development of a comprehensive and sensitive analytical method capable of analyzing multiple phenols in a single sample preparation and analytical run. Currently, no such method is available for multiple classes of phenols due to electrospray ionization (ESI) limitations in concurrent ionization and lack of sensitivity to certain phenols, particularly alkylphenols. In this study, we investigated the influence of mobile phase compositions in ESI on concurrent ionization and analytical sensitivity of liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS/MS) during the analysis of multiple classes of phenols, and we propose a comprehensive and sensitive analytical method for various classes of phenols (i.e., bisphenols, parabens, benzophenones, chlorophenols, and alkylphenols). The proposed method was affected by 0.5 mM ammonium fluoride under methanol conditions. It enabled the concurrent ionization of all the phenols and significantly improved the analytical sensitivity for bisphenols and alkylphenols, which typically have poor ionization efficiency. This method, combined with a "dilute and shoot" approach, allowed us to simultaneously quantify 38 phenols with good chromatographic behavior and sensitivity. Furthermore, the method was successfully applied to the analysis of 61 urine samples collected from aquatic (swimming) and land (indoor volleyball and outdoor football) athletes. • Fluoride-assisted LC–ESI–MS/MS method to determine multiclass phenols in urine. • Ammonium fluoride and methanol as a phenol-specialized mobile-phase composition. • Dramatic sensitivity enhancement of alkylphenols and bisphenols by fluoride ions. • Fast, simple and practical sample preparation without uncontrolled sample loss. • Successful application to 61 urine samples from athletes. [ABSTRACT FROM AUTHOR]

A rapid and direct paper spray ionization/mass spectrometry (PSI/MS) method was developed for quantitative analysis of ephedrine, pseudoephedrine, norpseudoephedrine, and methylephedrine in human urine. This method involves the use of a triangular filter paper and high-resolution mass spectrometry, where the molecular ions of ephedrines were generated by applying high voltage after loading the spray solvent to the paper which urine sample was pre-loaded. Small amounts (2 μL) of urine spiked with an internal standard were directly analyzed for ephedrines. The PSI/MS method was validated for linearity, within- and between-run precision, accuracy, and limit of detection. The results showed good linearity ( R 2 ≥ 0.9928) and acceptable precision and accuracy. Furthermore, the accuracy of the method was assessed by analyzing a blind urine sample from World Anti-Doping Agency and comparing the measured concentrations with the nominal concentrations. This test resulted in accuracies ranging from 96.4 to 106.1%, indicating that the PSI/MS method has the potential to be an alternative technique for the fast quantitation of ephedrines in doping control analysis. [ABSTRACT FROM AUTHOR]

Environmental pollutants (EPOLs), such as phthalates, volatile organic compounds, phenols, parabens, polycyclic aromatic hydrocarbons, pyrethroids, and environmental tobacco smoke, are highly heterogeneous compounds. Recently, attention has been drawn to the assessment of the combinatory effects of multiple EPs. To correlate multiple exposures with potential health implications, advanced comprehensive analytical methods covering multiclass EPOLs are essential. However, because of several technical problems associated with enzyme hydrolysis, simultaneous extraction, and multiresidue liquid chromatography–tandem mass spectrometry analysis, it is difficult to establish a comprehensive method covering a number of EPOLs in a single sample preparation and analytical run. We developed tandem hybrid hydrolysis, modified direct injection, and a comprehensive mobile phase to overcome these technical problems and established a comprehensive analytical method for simultaneous biomonitoring of multiclass EPOLs. Tandem hybrid hydrolysis using β-glucuronidase and consecutive acid hydrolysis allowed selective hydrolysis of glucuronide- and sulfate-conjugated metabolites without phthalate degradation. The comprehensive mobile phase composed of 0.01% acetic acid and acetonitrile enabled us to simultaneously analyze 86 EPOLs, with good chromatographic behavior and ionization efficiency. Modified direct injection allowed a small amount of sample and simultaneous urinary extraction. The method was validated and applied to 39 urine samples from 19 mother–newborn pairs for multiple exposure assessment. Results showed that BP-3, a general component in sunblock products, and monoethyl phthalate, a metabolite of diethyl phthalate, exhibit a clear positive correlation between mothers and newborns. Therefore, the developed method has potential as a novel analytical tool for long-term, large-scale, and data-rich human biomonitoring of EPOLs. • Comprehensive LC–ESI/MS/MS method for multiclass environmental pollutants. • Tandem hybrid hydrolysis and direct injection method without extraction. • Comprehensive mobile phase composition consisted of 0.01% acetic acid. • Analytical tool suitable for large-scale human biomonitoring. [ABSTRACT FROM AUTHOR]

Gangliosides, acidic glycosphingolipids with one or more sialic acid residues, are challenging to analyze with matrix-assisted laser desorption/ionization ( MALDI) mass spectrometry ( MS) because loss of sialic acid residues is significant during ionization process, especially in the positive-ion mode. Recently, we showed that 5-methoxysalicylic acid ( MSA) could be a matrix of choice for ganglioside analysis in the positive-ion mode. In this study, we investigated whether GD1a and GD1b, structural isomers with two sialic acid residues, are distinguishable by MALDI MS or tandem MS ( MS/ MS) with MSA and a proper salt additive. Our results showed that characteristic fragment ions of GD1a and GD1b were successfully observed by the positive-ion mode MALDI MS/ MS and these diagnostic ions were more reliably detected with increased intensities when an alkali earth metal additive such as CaCl2 was employed instead of an alkali metal additive such as NaCl. [ABSTRACT FROM AUTHOR]

Multiple condensers are used for dual-use open cycle ocean thermal energy conversion to generate both electric power and desalinated water with preset ratios. Fundamentals of heat and mass transfer phenomena are scrutinized to identify optimal operational conditions of various OC-OTEC plant scales. Important control parameters include warm water temperature and its intake rate, vacuum pressure in the evaporator, and cold water temperature. Intake rate of the cold deep seawater is estimated based on the operational mode and conditions. Performances of the multiple condenser OC-OTEC system, power generation and seawater desalination capacities are analytically evaluated in terms of steam flow fractions, temperature of intake seawater, and vacuum pressure. This research provides unprecedented levels of theoretical depth, mathematical details, and design criteria for highly optimized dual-use OC-OTEC operations. Future research directions for OC-OTEC technologies are also discussed in detail. [ABSTRACT FROM AUTHOR]

RATIONALE: Quantifying polymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) with a conventional crystalline matrix generally suffers from poor sample-to-sample or shot-toshot reproducibility. An ionic-liquid matrix has been demonstrated to mitigate these reproducibility issues by providing a homogeneous sample surface, which is useful for quantifying polymers. In the present study, we evaluated the use of an ionic liquid matrix, i.e., 1-methylimidazolium α-cyano-4-hydroxycinnamate (1-MeIm-CHCA), to quantify polyhexamethylene guanidine (PHMG) samples that impose a critical health hazard when inhaled in the form of droplets. METHODS: MALDI-TOF mass spectra were acquired for PHMG oligomers using a variety of ionic-liquid matrices including 1-MeIm-CHCA. Calibration curves were constructed by plotting the sum of the PHMG oligomer peak areas versus PHMG sample concentration with a variety of peptide internal standards. RESULTS: Compared with the conventional crystalline matrix, the 1-MeIm-CHCA ionic-liquid matrix had much better reproducibility (lower standard deviations). Furthermore, by using an internal peptide standard, good linear calibration plots could be obtained over a range of PMHG concentrations of at least 4 orders of magnitude. CONCLUSIONS: This study successfully demonstrated that PHMG samples can be quantitatively characterized by MALDI-TOFMS with an ionic-liquid matrix and an internal standard. [ABSTRACT FROM AUTHOR]

Abstract: Enzymatic conversion of arginine to citrulline by peptidyl arginine deiminase is associated with peptide presentation and development of autoimmunity in rheumatoid arthritis. In order to facilitate identification of the citrullination site, citrulline residue was modified using 4-bromophenyl glyoxal, and 194Da mass increase and incorporation of the Br signature were confirmed by MALDI-TOF MS. Using this approach, we identified four and five citrullination sites of bovine serum albumin and bovine fibrinogen, respectively. MALDI-TOF/TOF MS was used to unambiguously identify two citrullination sites from bovine fibrinogen. [Copyright &y& Elsevier]

Abstract: Precise proteomic profiling of limited levels of disease tissue represents an extremely challenging task. Here, we present an effective and reproducible microproteomic workflow for sample sizes of only 10,000 cells that integrates selective sample procurement via laser capture microdissection (LCM), sample clean-up and protein level fractionation using short-range SDS-PAGE, followed by ultrasensitive LC–MS/MS analysis using a 10μm i.d. porous layer open tubular (PLOT) column. With 10,000 LCM captured mouse hepatocytes for method development and performance assessment, only 10% of the in-gel digest, equivalent to ∼1000 cells, was needed per LC–MS/MS analysis. The optimized workflow was applied to the differential proteomic analysis of 10,000 LCM collected primary and metastatic breast cancer cells from the same patient. More than 1100 proteins were identified from each injection with >1700 proteins identified from three LCM samples of 10,000 cells from the same patient (1123 with at least two unique peptides). Label free quantitation (spectral counting) was performed to identify differential protein expression between the primary and metastatic cell populations. Informatics analysis of the resulting data indicated that vesicular transport and extracellular remodeling processes were significantly altered between the two cell types. The ability to extract meaningful biological information from limited, but highly informative cell populations demonstrates the significant benefits of the described microproteomic workflow. [Copyright &y& Elsevier]

• Fluoride-assisted LC–ESI/MS/MS method for propofol determination. • High sensitive and practical method without derivatization. • Direct quantitation of propofol with the limit of detection at 0.15 ng mL−1. • Simultaneous analysis of phase II metabolites. The misuse of propofol for recreational purposes has become a serious social issue. Accordingly, practical and sensitive analytical methods to investigate the chronic abuse and toxicity of propofol are required. However, current propofol determination methods using liquid chromatography-mass spectrometry (LC-MS/MS) suffer from problems associated with loss in sample preparation due to its volatility and its poor ionization efficiency and collision-induced dissociation in mass spectrometry. Herein, we have developed a sensitive and accurate fluoride-assisted LC-MS/MS method combined with direct-injection for propofol determination. Ionization via fluoride-ion attachment/induced deprotonation, effected by ammonium fluoride in the mobile phase, was found to dramatically improve the sensitivity of propofol without derivatization. Furthermore, direct injection without derivatization enables the simultaneous analysis of propofol and its phase II metabolites without analyte loss. The optimal concentration of ammonium fluoride in the mobile phase was found to be 1 mM under methanol conditions. The linearity is good (R2 ≥ 0.999) and the intra- and inter-day precisions for propofol determination are between 1.9 and 8.7%. The accuracies range from 87.5% to 105.4% and the limits of detection and quantitation for propofol in urine are 0.15 and 0.44 ng mL−1, respectively. The present method was successfully applied to human urine and showed a sufficient sensitivity to determine propofol and five phase II metabolites over 48 h in human urine after administration. Consequently, the fluoride-assisted LC-MS/MS method was demonstrated to be sensitive, accurate, and practical for the determination of propofol and its metabolites. [ABSTRACT FROM AUTHOR]

Many studies have analyzed nicotine metabolites in blood and urine to determine the toxicity caused by smoking, and assess exposure to cigarettes. Recently, hair and nails have been used as alternative samples for the evaluation of smoking, as not only do they reflect long-term exposure but they are also stable and easy to collect. Liquid-liquid or solid-phase extraction has mainly been used to detect nicotine metabolites in biological samples; however, these have disadvantages, such as the use of toxic organic solvents and complex pretreatments. In this study, a modified QuEChERS method was proposed for the first time to prepare samples for the detection of nicotine metabolite cotinine (COT) and trans-3′-hydroxycotinine (3-HCOT) in hair and nails. High-performance liquid chromatography–tandem mass spectrometry (LC–MS/MS) was used to analyze traces of nicotine metabolites. The established method was validated for selectivity, linearity, lower limit of quantitation, accuracy, precision and recovery. In comparison with conventional liquid-liquid extraction (LLE), the proposed method was more robust, and resulted in higher recoveries with favorable analytical sensitivity. Using this method, clinical samples from 26 Korean infants were successfully analyzed. This method is expected to be applicable in the routine analysis of nicotine metabolites for environmental and biological exposure monitoring. [ABSTRACT FROM AUTHOR]

The application of dried blood spots in clinical research is becoming increasingly popular owing to its convenient collection, storage, and transportation compared to that of conventional biological samples. The potential of trimethylamine N -oxide and its related compounds as biomarkers for various cardiovascular diseases, such as atherosclerosis, stroke, thrombosis, and heart failure, was recently highlighted, which was the driving force behind the development of an analytical method to identify trimethylamine N -oxide and eight related compounds in dried blood spots. In the proposed method, a novel "on-spot reaction" approach was introduced to overcome the low loading efficiency of trimethylamine in dried blood spots. Upon the addition of 50 μL of blood onto the filter paper pretreated with dilute HCl, an acid–base neutralization reaction in the blood spots transformed the volatile trimethylamine to a salt. Next, a punched disc with a diameter of 6.0 mm was eluted by agitation with 20 mM ammonium formate for 10 min and derivatized with 1.0 M ethyl bromoacetate at 80 °C for 60 min. A surrogate analyte approach was employed for quantification of these endogenous compounds in the complex matrix. Analysis was carried out using zwitterionic hydrophilic interaction liquid chromatography–high-resolution mass spectrometry. The established method was validated and applied to monitor real samples from 30 clinical cases. The proposed new methodology based on dried blood spots could greatly improve the convenience, analytical sensitivity, and selectivity of cardiovascular disease testing. Image 1 • DBS-based method to detect trimethylamine N -oxide-related compounds was proposed. • A novel on-spot reaction can improve loading efficiency of trimethylamine in DBS. • Chemical derivatization and surrogate analyte approach were employed. • The established method was validated and successfully applied in 30 real samples. • This can provide a simple approach to regular check-up for cardiovascular disease. [ABSTRACT FROM AUTHOR]

Ternary mixed valent bismuth oxides (Bi 2 O 4 -Bi 4 O 7 -BiO 2-x) with rich oxygen vacancy acting as electron mediator have been successfully prepared through one-pot hydrothermal strategy, which demonstrates greatly improved UV, visible, and near-infrared (NIR) light-driven photocatalytic performance for photodegradation of bisphenol A (BPA). • Bi 2 O 4 -Bi 4 O 7 -BiO 2-x with rich oxygen vacancy photocatalyst was fabricated. • Bi 2 O 4 -Bi 4 O 7 -BiO 2-x revealed enhanced full spectrum driven photocatalytic activity. • A full spectrum photocatalytic mechanism was proposed by experiments and DFT study. To fully utilize the solar light, photocatalyst with broad spectrum response from UV to near-infrared (NIR) is desirable. In this work, ternary mixed valent Bi 2 O 4 -Bi 4 O 7 -BiO 2-x with rich oxygen vacancy has been synthesized through one-pot hydrothermal treatment of NaBiO 3. The results showed that through adjusting the hydrothermal conditions, oxygen vacancy-rich Bi 2 O 4 -Bi 4 O 7 -BiO 2-x nanocomposites with much higher efficiency than single or mixed bismuth oxides (Bi 2 O 4 , Bi 4 O 7 , BiO 2-x and Bi 4 O 7 -BiO 2-x ,) can be synthesized for photocatalytic degradation of bisphenol A (BPA) under UV, visible, and NIR light irradiation. In addition, the liquid chromatography-mass spectrometer (LC–MS) characterization demonstrated that BPA was oxidized to 4-isopropenyphenol first and the rings were opened sequentially under NIR light irradiation. Further detection of reactive species indicated that holes, O 2 −, and OH were the main oxidizing species in the degradation system. The experimental observations and density functional theory (DFT) calculations suggested that both type-II and the Z-scheme charge transfer with oxygen vacancies as electrons and holes mediators were formed at the interfaces of Bi 2 O 4 , Bi 4 O 7 , and BiO 2-x , resulting in a very efficient separation of photogenerated charge carriers in the composite. This work adds to the growing potential of mixed valent bismuth oxides based photocatalysts and is expected to accelerate the pace of the development of new-generation photocatalysts with high efficiency utilizing full-spectrum solar light. [ABSTRACT FROM AUTHOR]