Positive-mode Electrospray Ionization Mass Spectrometry Research Articles

Simple and rapid determination of triclabendazole and its metabolites in bovine and goat muscle tissue.

Triclabendazole (TCB) is widely used for prevention and treatment of parasitic infections in animals. Improper use can result in drug residues in animal tissues and cause health problems to humans through consumption. A simple and reliable analytical method for the determination of TCB and its metabolites in bovine and goat muscle using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed and validated. Analytes were extracted using acetonitrile and purified using enhanced matrix removal cartridge. Chromatographic separation was carried out on a BEH Shield RP18 column. The analytes were detected in positive-mode electrospray ionization mass spectrometry using multiple reaction monitoring. Average recoveries of 96.1%-105.6% with coefficients of variation of 1.9%-8.4% were obtained at fortification levels of 0.5, 2.5, 25, and 50 μg/kg for TCB and 5.0, 25, 250, and 500 μg/kg for its metabolites (triclabendazole sulfoxide, triclabendazole sulfone, and keto-TCB). A good linear regression was obtained with the mixed standard solutions in the range of 0.05-20 μg/L for TCB and 0.5-200 μg/L for its metabolites. The limit of quantification and limit of detection ranged from 0.05 to 0.75 μg/kg and from 0.1 to 1.5μg/kg, respectively. Moreover, this method was successfully applied to 33 real samples.

Analysis of Amygdalin in Various Matrices Using Electrospray Ionization and Flowing Atmospheric-Pressure Afterglow Mass Spectrometry.

Amygdalin is a natural cyanogenic compound that plants produce in the fight against insects and herbivores. Excessive amounts of amygdalin by animals and humans can potentially lead to fatal intoxication. However, studies confirm that amygdalin has antitumor properties, including the ability to inhibit the proliferation of cancer cells and to induce their apoptosis. The analysis of amygdalin in various matrices is an important analytical problem today. The publication presents the methodology of direct determination of amygdalin in water, sewage, and biological materials using electrospray ionization mass spectrometry (ESI-MS) and a new analytical method using flowing atmospheric-pressure afterglow mass spectrometry (FAPA-MS). The methods of analyte pre-concentration using a magnetic, molecularly imprinted polymer (mag-MIP) and the influence of interferents on the recorded spectra were discussed. Analytical parameters in ESI-MS and FAPA-MS methods were established. The linearity range was 4.5 µg L−1–45 mg L−1 in positive mode ESI-MS and FAPA-MS. The limit of detection (LOD) for ESI-MS was 0.101 ± 0.003 µg L−1 and the limit of quantification (LOQ) was 0.303 ± 0.009 µg L−1. In FAPA-MS, the LOD was 0.050 ± 0.002 µg L−1 and the LOQ was 0.150 ± 0.006 µg L−1. The content of amygdalin in various matrices was determined.

Analysis of oligonucleotides by ion-pair reversed-phase liquid chromatography coupled with positive mode electrospray ionization mass spectrometry.

Oligonucleotides are usually analyzed by ion-pair reversed-phase liquid chromatography (IP-RPLC) coupled with negative mode electrospray ionization mass spectrometry (ESI-MS) due to their highly negative charged phosphodiester backbones. Herein, the signal suppression effect of triethylamine (TEA) adducts caused the ion-pair reagent TEA/hexafluoroisopropanol (HFIP) is greatly alleviated after improving the in-source energy in positive mode ESI-MS. This strategy is applied for different RNA sequencing through analyzing their formic acid hydrolysates via IP-RPLC MS. Comparing with negative ion mode, we demonstrate that IP-RPLC MS analysis in positive ion mode is more suitable for RNA sequencing with fewer contaminant interferences. Finally, simultaneous online separation and detection of oligonucleotides and protein digests are achieved in positive ion mode IP-RPLC MS analysis with little interference to each other.

Residential water-soluble organic gases: chemical characterization of a substantial contributor to indoor exposures.

Characterization of residential indoor air is important to understanding exposures to airborne chemicals. While it is well known that non-polar VOCs are elevated indoors, polar VOCs remain poorly characterized. Recent measurements showed that total polar water-soluble organic gas (WSOG) concentrations are also much higher indoors than directly outdoors (on average 15× greater at 13 homes, on a carbon-mass basis). This work aims to chemically characterize these WSOG mixtures. Acetic, lactic, and formic acids account for 41% on average (30-54% across homes), of the total WSOG-carbon collected inside each home. Remaining WSOGs were characterized via high-resolution positive-mode electrospray ionization mass spectrometry. In total, 98 individual molecular formulas were detected. On average 67% contained the elements CHO, 11% CHN, 11% CHON, and 11% contained sulfur, phosphorus, or chlorine. Some molecular formulas are consistent with compounds having known indoor sources such as diethylene glycol (m/z+ 117.091, C4H10O3), hexamethylenetetramine (m/z+ 141.113, C6H12N4), and methacrylamide (m/z+ 86.060, C4H7NO). Exposure pathways, potential doses, and implications are discussed.

Structural Diversity of Nucleosomes Characterized by Native Mass Spectrometry.

Histone tails, which protrude from nucleosome core particles (NCPs), play crucial roles in the regulation of DNA transcription, replication, and repair. In this study, structural diversity of nucleosomes was investigated in detail by analyzing the observed charge states of nucleosomes reconstituted with various lengths of DNA using positive-mode electrospray ionization mass spectrometry (ESI-MS) and molecular dynamics (MD) simulation. Here, we show that canonical NCPs, having 147 bp DNA closely wrapped around a histone octamer, can be classified into three groups by charge state, with the least-charged group being more populated than the highly charged and intermediate groups. Ions with low charge showed small collision cross sections (CCSs), suggesting that the histone tails are generally compact in the gas phase, whereas the minor populations with higher charges appeared to have more loosened structure. Overlapping dinucleosomes, which contain 14 histone proteins closely packed with 250 bp DNA, showed similar characteristics. In contrast, mononucleosomes reconstituted with a histone octamer and longer DNA (≥250 bp), which have DNA regions uninvolved in the core-structure formation, showed only low-charge ions. This was also true for dinucleosomes with free DNA regions. These results suggest that free DNA regions affect the nucleosome structures. To investigate the possible structures of NCP observed in ESI-MS, computational structural calculations in solution and in vacuo were performed. They suggested that conformers with large CCS values have slightly loosened structure with extended tail regions, which might relate to the biological function of histone tails.

Identification of an Eight-Electron Superatomic Cluster and Its Alloy in One Co-crystal Structure

Herein we report a crystal structure of [Au0.5Ag0.5@Ag20{S2P(OiPr)2}12](PF6) [Cl@Ag8{S2P(OiPr)2}6](PF6) (1), which compositions were supported by positive-mode electrospray ionization mass spectrometry. The structural elucidation indicates that the encapsulated atom of an Ag13 the entered icosahedron can be replaced by a gold atom. Surprisingly, the capping Ag atoms on the surface of an icosahedron in 1 reveal a different arrangement from the previously reported [Ag21{S2P(OiPr)2}12](PF6) of C3 symmetry. Besides, the preference for the central silver atom being oxidized by Au(I) is rationalized by the DFT calculations on three different computed [AuAg20{S2PH2}12]+ models having C1, C3, and T symmetry, respectively.

Determination of true ratios of different N-glycan structures in electrospray ionization mass spectrometry

An ideal method for the analysis of N-glycans would both identify the isomeric structure and deliver a true picture of the relative, if not absolute, amounts of the various structures in one sample. Porous graphitic carbon chromatography coupled with electrospray ionization mass spectrometry (ESI-MS) detection has emerged as a method with a particularly high potential of resolving isomeric oligosaccharides, but little attention has so far been paid to quantitation of the results obtained. In this work, we isolated a range of structures from Man5 to complex type N-glycans with zero to four sialic acids and blended them into an equimolar “glyco tune mix”. When subjected to liquid chromatography–ESI-MS in positive and negative modes, the glyco tune mix clearly demonstrated the futility of quantitation of N-glycans of different overall composition, different number of sialic acids, and strongly differing size without compensation for their very different molar responses. Relative quantitation of human plasma N-glycans was performed with correction factors deduced from this external glyco tune mix. Addition of just one isotope-coded internal standard with enzymatically added 13C-galactose led to absolute quantification in the same experiment.Graphical Discrepancy between desirable (grey bars) and real (green bars) relative ion abundance of equimolar amounts of glycans in positive mode ESI-MS.

Circular Dichroism and Voltammetry, Assisted by Multivariate Curve Resolution, and Mass Spectrometry of the Competitive Metal Binding by Phytochelatin PC5

The competitive binding of Cd(2+) and Pb(2+) by the phytochelatin (γGlu-Cys)5-Gly (PC5) has been examined by several analytical techniques. Positive-mode electrospray ionization mass spectrometry (ESI-MS) is used to determine the stoichiometries of the complexes, while voltammetric and spectroscopic data are analyzed by multivariate curve resolution with alternating least-squares (MCR-ALS) and some recently developed chemometric tools, which allows one to follow the displacement induced by Cd(2+) or Pb(2+) in the binding of Pb(2+) or Cd(2+), respectively, by PC5, and to obtain a complete overview of the processes involved. Differential pulse polarography (DPP) signals of these systems present, besides overlapping peaks due to free metal ion and metal complexes, interference of mercury anodic signals. Circular dichroism (CD) spectroscopy is a useful complementary technique due to the absence of these types of signals and its selective response to different species. A tentative complexation/electrochemical model is proposed for Cd(2+) and Pb(2+) competition toward PC5 complexation. The formation of the previously unreported ternary CdPb(PC5) complex was suggested by DPP and CD spectroscopy experiments and confirmed by ESI-MS.

Detection of nucleotides in positive-mode electrospray ionization mass spectrometry using multiply-charged cationic ion-pairing reagents

Nucleotides are a class of molecules that play an essential role in biological systems. A new method has been developed in the detection of nucleotides. These molecules can exist as monomers or constituents of oligomers and polymers. As such, they carry from one to several negative charges. In this study, different cationic ion-pairing reagents were used to complex with each of the 28 nucleotide monomers and nucleotide containing compounds. By using this method, this discrete set of anions was able to be detected in the positive-mode electrospray ionization mass spectrometry, as positively charged complexes. Tandem mass spectrometry experiments were also completed on the ion-pairing reagents that performed the best in the single ion monitoring (SIM) ion mode, and the sensitivity was lowered even further for most of the anions. Limits of detection for compounds such as thymidine diphosphate were improved as much as 100 times compared to the positive SIM mode, and 750 times when compared to the negative mode. A few nucleotides did not show a significant increase in sensitivity when analyzed in the positive ion mode, but in general the new method developed herein resulted in a much greater sensitivity than traditional detection in the negative mode.

Evaluation of tetracationic salts as gas‐phase ion‐pairing agents for the detection of trivalent anions in positive mode electrospray ionization mass spectrometry

In previous studies, new electrospray ionization mass spectrometry (ESI-MS) approaches were developed for the highly sensitive detection of singly and doubly charged anions in positive mode ESI-MS by using specially synthesized dicationic and tricationic ion-pairing agents, respectively. By detecting the positively charged ion complex in the positive mode, limits of detection (LODs) for the anions can be lowered by several magnitudes. In this work, we used eighteen newly synthesized tetracationic ion-pairing agents, constructed with different geometries, linkages and cation moieties, for the detection of eighteen triply charged anions of different structural motifs. The LODs for these anions were from ten to several thousand times lower in the positive selective ion monitoring (SIM) mode than in the negative mode. These tetracationic agents also were shown to be useful for the detection of -1 and -2 anions. In addition, the LODs for -3 anions can be further lowered by monitoring the product fragments of the ion-pairing complexes in the single reaction monitoring (SRM) mode.