Specificity enhancement by electrospray ionization multistage mass spectrometry – a valuable tool for differentiation and identification of ‘V’‐type chemical warfare agents

The use of chemical warfare agents has become an issue of emerging concern. One of the challenges in analytical monitoring of the extremely toxic ‘V’‐type chemical weapons [O‐alkyl S‐(2‐dialkylamino)ethyl alkylphosphonothiolates] is to distinguish and identify compounds of similar structure. MS analysis of these compounds reveals mostly fragment/product ions representing the amine‐containing residue. Hence, isomers or derivatives with the same amine residue exhibit similar mass spectral patterns in both classical EI/MS and electrospray ionization‐MS, leading to unavoidable ambiguity in the identification of the phosphonate moiety. A set of five ‘V’‐type agents, including O‐ethyl S‐(2‐diisopropylamino)ethyl methylphosphonothiolate (VX), O‐isobutyl S‐(2‐diethylamino)ethyl methylphosphonothiolate (RVX) and O‐ethyl S‐(2‐diethylamino)ethyl methylphosphonothiolate (VM) were studied by liquid chromatography/electrospray ionization/MS, utilizing a QTRAP mass detector. MS/MS enhanced product ion scans and multistage MS³ experiments were carried out. Based on the results, possible fragmentation pathways were proposed, and a method for the differentiation and identification of structural isomers and derivatives of ‘V’‐type chemical warfare agents was obtained. MS/MS enhanced product ion scans at various collision energies provided information‐rich spectra, although many of the product ions obtained were at low abundance. Employing MS³ experiments enhanced the selectivity for those low abundance product ions and provided spectra indicative of the different phosphonate groups. Study of the fragmentation pathways, revealing some less expected structures, was carried out and allowed the formulation of mechanistic rules and the determination of sets of ions typical of specific groups, for example, methylphosphonothiolates versus ethylphosphonothiolates. The new group‐specific ions elucidated in this work are also useful for screening unknown ‘V’‐type agents and related compounds, utilizing precursor ion scan experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Electrochemical oxidation and cleavage of peptides analyzed with on-line mass spectrometric detection

An on-line electrochemistry/electrospray mass spectrometry system (EC/MS) is described that allows fast analysis of the oxidation products of peptides. A range of peptides was oxidized in an electrochemical cell by application of a potential ramp from 0 to 1.5 V during passage of the sample. Electrochemical oxidation of peptides was found to occur readily when tyrosine was present. Tyrosine was found to be oxidized between 0.5 and 1.0 V to various oxidation products, including peptide fragments formed by hydrolysis at the C-terminal side of tyrosine. The results confirm earlier knowledge on the mechanisms and reaction products of chemical and electrochemical peptide oxidation. Methionine residues are also readily oxidized, but do not induce peptide cleavage. At potentials higher than about 1.1 V, additional oxidation products were observed in some peptides, including loss of 28 Da from the C-terminus and dimerization. The tyrosine-specific cleavage reaction suggests a possible use of the EC/MS system as an on-line protein digestion and peptide mapping system. In addition, the system can be used to distinguish phosphorylated from unphosphorylated tyrosine residues. Four forms of the ZAP-70 peptide ALGADDSYYTAR with both, either or neither tyrosine phosphorylated were subjected to a 0-1.5 V potential ramp. Oxidation of, and cleavage adjacent to, tyrosine was observed exclusively at unphosphorylated tyrosine residues.     

On‐Line Electrochemistry/Electrospray Ionization Mass Spectrometry (EC/ESI‐MS) for the Generation and Identification of Nucleotide Oxidation Products

The oxidation behavior of DNA and RNA nucleotides is studied by an on‐line set‐up consisting of an electrochemical thin‐layer cell (EC) directly coupled to electrospray ionization mass spectrometry (ESI‐MS). This set‐up allows the generation of nucleotide oxidation products in the electrochemical cell at increasing potentials. Moreover, the products are determined directly, without isolation or derivatization steps, by electrospray ionization time of flight mass spectrometry (ESI‐ToF/MS). The dependence of the mass spectra on the applied potential is displayed as ‘mass voltammograms’. An advanced set‐up, consisting of the electrochemical cell coupled to electrospray ionization tandem mass spectrometry (EC/ESI‐MS/MS) allows further structure elucidation based on fragmentation experiments. The electrochemical conversion is performed using a boron doped diamond (BDD) working electrode, which is known to generate hydroxyl radicals at high potentials. The capability of the EC‐MS system to generate highly relevant oxidation products which also occur upon oxidative damage in vivo is demonstrated in this study by the formation of well known biomarkers for DNA damage, including 2′‐deoxy‐8‐oxo‐guanosine 5′‐monophosphate.     

Structural determination of the novel fragmentation routes of morphine opiate receptor antagonists using electrospray ionization quadrupole time-of-flight tandem mass spectrometry

Electrospray ionization quadrupole time-of-flight (ESI-QqToF) mass spectra of naltrindole hydrochloride 1, naltriben mesylate 2, and naltrexone hydrochloride 3, a common series of morphine opiate receptor antagonists, were recorded using different declustering potentials. Low-energy collision-induced dissociation (CID) MS/MS experiments established the fragmentation routes of these compounds. In addition, re-confirmation of the various established fragmentation routes was effected by conducting a series of ESI-CID-QqTof-MS/MS experiments using non-conventional quasi MS(n) (up to MS8) product ion scans, which were initiated by CID in the atmospheric pressure/vacuum interface using a higher declustering potential. Precursor ion scan analyses were also performed with a conventional quadrupole-hexapole-quadrupole tandem mass spectrometer and allowed the confirmation of the genesis of some diagnostic ions.     

Comparison of GC–MS and MEKC methods for caffeine determination in preworkout supplements

In this study, GC–MS‐ and MEKC‐based methods for determination of caffeine (CAF) in preworkout supplements were developed and validated. The proposed protocols utilized minimal sample preparation (simple dilution and syringe filtration). The developed methods achieved satisfactory validation parameters, i.e. good linearity (R² > 0.9988 and R² > 0.9985 for GC–MS‐ and MEKC‐based method, respectively), satisfactory intra‐ and interaccuracy (within 92.6–100.7% for method utilizing GC–MS and 92.1–110.3% for protocol based on MEKC) and precision (CV < 15.9% and CV < 6.3% for GC–MS‐ and MEKC‐based method, respectively) and recovery (within 100.1–100.8% for method utilizing GC–MS and 101.5–106.2% for protocol based on MEKC). The LOD was 0.03 and 3 μg/mL for method utilizing GC–MS and MEKC, respectively. The CAF concentrations determined by GC–MS‐ and MEKC‐based methods were found to be in the range of 8.53–11.23 and 8.20–11.61 μg/mL, respectively. Taking into consideration information on the labels, the investigated supplements were found to contain from 110.0 to 167.3% of the declared CAF content, which confirmed the literature reports on incompatibility of the declared product compositions with real ones. Nevertheless, the consumption of examined supplements as recommended by producers did not lead to exceeding the CAF safe limit of 400 mg per day. Additionally, the MEKC‐based method allowed for detection and identification of vitamin B3 and B6 in all of the investigated supplement samples, which demonstrated that MEKC‐based protocols may be an appropriate assays for simultaneous determination of CAF and vitamins.     

A flow system with an electrochemical reduction cell for spectrophotometric determinations of major constituents in Fe/V alloys

Insertion of an electrochemical cell in a flow injection system to evaluate the on-line reduction of ionic species is presented. The cell comprised Pt electrodes installed in two sections separated by a Nafion membrane. The sample was injected into an acidic carrier stream and passed through the cathode compartment of the electrolytic chamber where the species were reduced as consequence of an applied DC voltage. The sample solution leaving the cell received a confluent reagent stream (1,10-phenanthroline buffered at pH 4.7) and the reacted products were dropped off in an open tube for gas/liquid separation. Efficiency of the Fe(3+) to Fe(2+) reduction in acidic medium was evaluated in the presence of strongly reducing species of V and Mo by monitoring the Fe(II) colored complex. Interferences from Pb(2+), Co(2+), Ni(2+), Zn(2+), Cu(2+), V(5+) and Mo(6+) were evaluated. Production of strongly reducing species of V at the electrolytic cell presented higher efficiency for Fe reduction than the electrolytic chamber itself. Total reduction of Fe(3+) in solutions containing up to 10 mg l(-1) Fe plus 100 mg l(-1) V or 100 mg l(-1) of Mo was achieved by the electrolytic process at 2 A. The quantitative determination of Fe and V in low silicon Fe/V alloys was achieved. Accuracy was assessed with the certified Euro-standard 577-1 ferrovanadium alloy produced by the Bureau of Analysed Samples Limited and no difference at the 95% confident level was found.     

镀锡电解液中有机添加剂的电化学氧化

应用循环伏安法(CV)研究镀锡液有机添加剂PSA(苯酚磺酸)、EN(α-萘酚聚氧乙烯醚)和ENSA(α-萘酚磺酸聚氧乙烯醚)的阳极伏安行为.实验证明,PSA溶液在1.2 V附近产生一个阳极氧化峰,EN和ENSA溶液在0.95 V和1.3 V都出现阳极氧化峰.恒电流电解后用HPLC(高效液相色谱)和EI/MS(电子轰击质谱)分析该有机添加剂的阳极氧化产物,讨论其相关的电化学反应机理.     

Structural elucidation of V‐type nerve agents by liquid chromatography/electrospray ionization mass spectrometry

V‐nerve agents present information‐poor spectra, both in GC‐EI‐MS and LC‐ESI‐MS/MS, with dominant fragments/product ions corresponding to the amine‐containing residue. Hence, derivatives/isomers with the same amine residue exhibit similar mass spectral patterns, leading to ambiguity in the phosphonate structure. We present a simple approach for their structural elucidation based on two complementary experiments: ESI‐MS/MS of the original compound, which provides information about the amine moiety, and ESI‐MS/MS of the phosphonic acid hydrolysis products generated by N‐iodosuccinimide, which provides ions' characteristic of the phosphonate structure. This approach enables the structural elucidation of the original V‐agents with a higher degree of certainty.     

Structural determination of the novel fragmentation routes of zwitteronic morphine opiate antagonists naloxonazine and naloxone hydrochlorides using electrospray ionization tandem mass spectrometry

Electrospray ionization quadrupole time-of-flight (ESI-QqToF) mass spectra of the zwitteronic salts naloxonazine dihydrochloride 1 and naloxone hydrochloride 2, a common series of morphine opiate receptor antagonists, were recorded using different declustering potentials. The singly charged ion [M+H-2HCl](+) at m/z 651.3170 and the doubly charged ion [M+2H-2HCl](2+) at m/z 326.1700 were noted for naloxonazine dihydrochloride 1; and the singly charged ion [M+H-HCl](+) at m/z 328.1541 was observed for naloxone hydrochloride 2. Low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) experiments established the fragmentation routes of these compounds. In addition to the characteristic diagnostic product ions obtained, we noticed the formation of a series of radical product ions for the zwitteronic compounds 1 and 2, and also the formation of a distonic ion product formed from the singly charged ion [M+H-HCl](+) of naloxone hydrochloride 2. Confirmation of the various established fragmentation routes was effected by conducting a series of ESI-CID-QqTof-MS/MS product ion scans, which were initiated by CID in the atmospheric pressure/vacuum interface using a higher declustering potential. Deuterium labeling was also performed on the zwitteronic salts 1 and 2, in which the hydrogen atoms of the OH and NH groups were exchanged with deuterium atoms. Low-energy CID-QqTof-MS/MS product ion scans of the singly charged and doubly charged deuteriated molecules confirmed the initial fragmentation patterns proposed for the protonated molecules. Precursor ion scan analyses were also performed with a conventional quadrupole-hexapole-quadrupole tandem mass spectrometer and allowed the confirmation of the genesis of some diagnostic ions.     

Investigation of the electrochemical oxidation products of zotepine and their fragmentation using on-line electrochemistry/electrospray ionization mass spectrometry

When zotepine, an antipsychotic drug, was electrochemically oxidized using electrospray ionization mass spectrometry (ESI-MS) coupled with a microflow electrolytic cell, [M + 16 + H]+ (m/z 348), [M-H]+ (m/z 330) and [M-14 + H]+ (m/z 318) were observed as electrochemical oxidation product ions (M represents the zotepine molecule). Although a major fragment ion that was derived from the dimethyl aminoethyl moiety was observed only at m/z 72 in the collision-induced dissociation (CID) spectrum of zotepine, new fragments such as m/z 315 and 286 ions could be generated in the CID spectrum by combining electrochemical oxidation and CID. Since these fragments were relatively specific with high ion strength, it was thought that they would be useful for developing a sensitive LC-MS/MS assay. The S-oxide and N-demethylated products were detected by electrolysis assuring that a portion of P450 metabolites of zotepine could be mimicked by the electrochemistry/electrospray ionization mass spectrometry (EC/ESI-MS) system.     

Electrolysis-reducing electrodes for electrokinetic devices

Direct current electrokinetic systems generally require Faradaic reactions to occur at a pair of electrodes to maintain an electric field in an electrolyte connecting them. The vast majority of such systems, e.g. electrophoretic separations (capillary electrophoresis) or electroosmotic pumps (EOPs), employ electrolysis of the solvent in these reactions. In many cases, the electrolytic products, such as H+ and OH? in the case of water, can negatively influence the chemical or biological species being transported or separated, and gaseous products such as O? and H? can break the electrochemical circuit in microfluidic devices. This article presents an EOP that employs the oxidation/reduction of the conjugated polymer poly(3,4-ethylenedioxythiophene), rather than electrolysis of a solvent, to drive flow in a capillary. Devices made with poly(3,4-ethylenedioxythiophene) electrodes are compared with devices made with Pt electrodes in terms of flow and local pH change at the electrodes. Furthermore, we demonstrate that flow is driven for applied potentials under 2?V, and the electrodes are stable for potentials of at least 100?V. Electrochemically active electrodes like those presented here minimize the disadvantage of integrated EOP in, e.g. lab-on-a-chip applications, and may open new possibilities, especially for battery-powered disposable point-of-care devices.     

乙二醇在电解银表面的氧化

用超高真空程序升温反应谱和瞬时应答方法研究了乙二醇在电解银表面的氧化，实验表明，室温下乙二醇吸附在电解银表面，并在３４３Ｋ分解给出一组产物群，预吸附氧与乙二醇反应时，在３４３Ｋ，４３３Ｋ和６１２Ｋ处给出三组产物群，它们分别对应于不同的表面反应，并给出了电解银催化乙二醇制乙二醛的活性结果。     

Confirmation of sulfamethazine, sulfathiazole, and sulfadimethoxine residues in condensed milk and soft-cheese products by liquid chromatography/tandem mass spectrometry

A liquid chromatography/tandem mass spectrometry method (LC/MS/MS) is described for the simultaneous detection of 3 sulfonamide drug residues at 1.25 ppb in condensed milk and soft-cheese products. The 3 sulfonamide drugs of interest are sulfathiazole (STZ), sulfamethazine (SMZ), and sulfadimethoxine (SDM). The method includes extraction of the product with phosphate buffer, centrifugation of the diluted product, and application of a portion of the extract onto a polymeric solid-phase extraction cartridge. The cartridge is washed with water, and the sulfonamides are eluted with methanol. After evaporation, the residue is dissolved in 0.1% formic acid solution, and the solution is filtered before analysis by LC/MS/MS. The LC/MS/MS program involved a series of time-scheduled selected-reaction monitoring transitions. The transitions of MH+ to the common product ions at m/z 156, 108, and 92 were monitored for each residue. In addition, SMZ and SDM had a fourth significant and unique product ion transition that could be measured. Validation was performed with control and fortified-control condensed bovine milk with 2.5, 5, and 10 ppb sulfonamides. This method was applied to imported flavored and unflavored condensed milk and cream cheese bars. The presence of STZ and SMZ residues was confirmed in 3 out of 6 products.     

A chip-type thin-layer electrochemical cell coupled with capillary electrophoresis for online separation of electrode reaction products

A coupling technique of thin-layer electrolysis with high-performance capillary electrophoresis/UV–vis technique(EC/HPCE/UV–vis) is developed for online separation and determination of electrode reaction products. A chip-type thin-layer electrolytic (CTE) cell was designed and fabricated, which contains a capillary channel and a background electrolyte reservoir, allowing rapid electrolysis, direct sampling and online electrophoretic separation. This chip-type setup was characterized based on an electrophoresis expression of Nernst equation that was applied to the redox equilibrium of o-tolidine at different potentials. The utility of the method was demonstrated by separating and determining the electro-oxidation products of quercetin in different pH media. Two main products were always found in the studied time, potential and pH ranges. The variety of products increased not only with increasing potential but also with increasing pH value, and in total, at least 13 products were observed in the electropherograms. This work illustrates a novel example of capillary electrophoresis used online with thin-layer electrolysis to separate and detect electrode reaction products.     

Analysis of pesticide residues in fruits, vegetables, and milk by gas chromatography/tandem mass spectrometry.

A method for detection, quantitation, and confirmation of more than 100 pesticides by gas chromatography (GC) with ion trap mass spectrometry (MS/MS) has been developed. The sensitivity of this method for many analytes is equal to or lower than those of selective GC detectors such as flame photometric detectors and electrolytic conductivity detectors. Using MS/MS, very low detection limits and good confirmation (1 precursor ion and 2 or more product ions) are achieved simultaneously. The entire list of pesticides is screened with 2 injections per sample. Samples are introduced onto the column by a temperature-programmed cold injection to maximize response. Each pesticide is run with its own unique set of parameters, which fragment the compound, retaining only the precursor ion. This ion is then refragmented to create a product spectrum. The selectivity of MS/MS gives a very clean spectrum, making compound identification and confirmation clear, even with a relatively dirty food matrix. If care is taken to maintain the injection port and guard column, this method can reliably identify and confirm more than 100 pesticides at the low parts-per-billion range.     

Mechanistic study of colchicine's reduction behavior

Electrochemistry/mass spectrometry (EC/MS) using two different types of electrolytic cells was employed for the systematic mechanistic study of colchicine's reduction, both in aqueous and non-aqueous media. In aqueous media, at around − 1 V vs. Ag/AgCl, colchicine suffers a single-electron reduction to a transient anion radical, which after a follow-up protonation leads to a neutral free radical (E_rC_i mechanism). Depending on the experimental conditions, the latter undergoes some dimerization. At more negative potentials (− 1.4 V vs. Ag/AgCl) and pH < 7, the free radical is undergoing another single-electron reduction and a subsequent protonation. In the absence of protons (aprotic media), the one-electron reduction gives the anion radical. This process becomes fully reversible at high scan rates (≥ 10 V/s).     

Rapid screening and identification of cytochalasins by electrospray tandem mass spectrometry

The cytochalasin class of fungal metabolites was analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) with the aim of developing a methodology for their rapid identification in microbial extracts. ESI-MS analyses of reference cytochalasins were performed and several product ions were produced in MS/MS experiments on parent ions that are structurally characteristic. A precursor ion search was performed to detect cytochalasins in an ethyl acetate extract of fungal strain RK97-F21. Three cytochalasins were detected and one of the components was identified as epoxycytochalasin H by comparing the tandem mass spectra of the product ions with those of reference compounds. This finding was further validated by LC/MS and LC/MS/MS experiments.     

Adsorption Study of CO2 on Reticulated Vitreous Carbon (RVC) Covered with Platinum

Abstract

An electrode consisting of platinized reticulated vitreous carbon (Pt/RVC) which behaves as a conventional platinized platinum electrode is described. The Pt/RVC electrode has been used to study the products of CO₂ reduction by H_ad at potentials below 0.0V vs. NHE in acidic solution. Formic acid is proposed as the main product of this reaction.     

Products of SO2 adsorption on fuel cell electrocatalysts by combination of sulfur K-edge XANES and electrochemistry

Electrochemical adsorption of SO(2) on platinum is complicated by the change in sulfur oxidation state with potential. Here, we attempt to identify SO(2) adsorption products on catalyst coated membranes (CCMs) at different electrode potentials using a combination of in situ sulfur K-edge XANES (X-ray absorption near-edge structure) spectroscopy and electrochemical techniques. CCMs employed platinum nanoparticles supported on Vulcan carbon (Pt/VC). SO(2) was adsorbed from a SO(2)/N(2) gas mixture while holding the Pt/VC-electrode potential at 0.1, 0.5, 0.7, and 0.9 V vs a reversible hydrogen electrode (RHE). Sulfur adatoms (S(0)) are identified as the SO(2) adsorption products at 0.1 V, while mixtures of S(0), SO(2), and sulfate/bisulfate ((bi)sulfate) ions are suggested as SO(2) adsorption products at 0.5 and 0.7 V. At 0.9 V, SO(2) is completely oxidized to (bi)sulfate ions. The identity of adsorbed SO(2) species on Pt/VC catalysts at different electrode potentials is confirmed by modeling of XANES spectra using FEFF8 and a linear combination of experimental spectra from sulfur standards. Results on SO(2) speciation gained from XANES are used to compare platinum-sulfur electronic interactions for Pt(3)Co/VC versus Pt/VC catalysts in order to understand the difference between the two catalysts in terms of SO(2) contamination.