Atmospheric pressure chemical ionization of fluorinated phenols in atmospheric pressure chemical ionization mass spectrometry, tandem mass spectrometry, and ion mobility spectrometry

Atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) for fluorinated phenols (C6H5-xFxOH Where x = 0-5) in nitrogen with Cl- as the reagent ion yielded product ions of M Cl- through ion associations or (M-H)- through proton abstractions. Proton abstraction was controllable by potentials on the orifice and first lens, suggesting that some proton abstraction occurs through collision induced dissociation (CID) in the interface region. This was proven using CID of adduct ions (M Cl-) with Q2 studies where adduct ions were dissociated to Cl- or proton abstracted to (M-H)-. The extent of proton abstraction depended upon ion energy and structure in order of calculated acidities: pentafluorophenol > tetrafluorophenol > trifluorophenol > difluorophenol. Little or no proton abstraction occurred for fluorophenol, phenol, or benzyl alcohol analogs. Ion mobility spectrometry was used to determine if proton abstraction reactions passed through an adduct intermediate with thermalized ions and mobility spectra for all chemicals were obtained from 25 to 200 degrees C. Proton abstraction from M Cl- was not observed at any temperature for phenol, monofluorophenol, or difluorophenol. Mobility spectra for trifluorophenol revealed the kinetic transformations to (M-H)- either from M Cl- or from M2 Cl- directly. Proton abstraction was the predominant reaction for tetra- and penta-fluorophenols. Consequently, the evidence suggests that proton abstraction occurs from an adduct ion where the reaction barrier is reduced with increasing acidity of the O-H bond in C6H5-xFxOH.     

Investigations of taxoids by electrospray and atmospheric pressure chemical ionization with tandem mass spectrometry

The fragmentation behavior of taxoids was studied using electrospray (ESI) and atmospheric pressure chemical ionization (APCI) sources with multi-stage tandem mass spectrometry. In the positive ion mode taxoids gave prominent [M+Na]+ and [M+K]+ ions with the ESI source, and [M+NH4]+ or [M+H]+ ions with the APCI source. The MS/MS fragmentations of ions produced by APCI and ESI sources were very similar. For both sources, the presence of cinnamoyl or benzoyl groups could be characterized by initial losses of 148 or 122 u, respectively, from molecular adduct ions. However, the elimination of cinnamic acid was relatively difficult for the molecular adduct ions formed by APCI, and was comparable in importance to the loss of acetic acid. The other fragments involved losses of CH2CO, CO, and H2O. The 5/7/6 type taxoids underwent characteristic losses of 58 or 118 u from ions produced by both APCI and ESI sources. The fragmentation behavior was remarkably influenced by substitution locations. The elimination of the C-10 benzoyl group was usually the first fragmentation step, while that of the C-2 benzoyl group was relatively difficult. The acetoxyl group at C-7 was more active than those at C-2, C-9, and C-10, which in turn were more active than that at C-4. These fragmentation rules could facilitate the rapid screening and structural characterization of taxoids in plant extracts by high-performance liquid chromatography/mass spectrometry (HPLC/MS).     

Study of atmospheric pressure chemical ionization of PETN by ion mobility spectrometry/tandem mass spectrometry

We present the results of studying the effects of temperature and humidity of the reaction medium and the intensity of ultraviolet radiation on the atmospheric pressure chemical ionization of Penthrite. The peculiarities of the ion mobility spectra of this compound obtained by ion mobility spectrometry-tandem mass spectrometry are analyzed.     

Probing the mechanism of the Petasis olefination reaction by atmospheric pressure chemical ionization mass and tandem mass spectrometry

Atmospheric pressure chemical ionization mass (APCI-MS) and tandem mass spectrometry (APCI-MS/MS) is used to probe the mechanism of the Petasis olefination reaction. Oxatitanacycle intermediates 4 were transferred from solution to the gas phase, detected as 4H+ by APCI-MS with characteristic Ti-isotopic patterns, and structurally characterized by APCI-MS/MS. Detection of 4H+, which upon collision activation dissociates to both 3H+ and Cp(2)TiOH+, fully supports the Hughes mechanism as depicted above. [reaction: see text]     

Precursor ion scan profiles of acylcarnitines by atmospheric pressure thermal desorption chemical ionization tandem mass spectrometry

The fatty acyl esters of L-carnitine (acylcarnitines) are useful biomarkers for the diagnosis of some inborn errors of metabolism analyzed by liquid chromatography/tandem mass spectrometry. In this study the acylcarnitines were analyzed by atmospheric pressure thermal desorption chemical ionization using a commercial tandem mass spectrometer (APTDCI-MS/MS). The method is based on the precursor ion scan mode determination of underivatized acylcarnitines desorbed from samples by a hot desolvation gas flow and ionized by a corona pin discharge. During desorption/ionization step the temperature induces the degradation of acylcarnitines; nevertheless, the common fragment to all acylcarnitines [MH-59](+) is useful for analyzing their profile. APTDCI parameters, including angle of collection and incidence, gas flows and temperatures, were optimized for acylcarnitines. The experiments were performed drying 2 microL of an equimolar mixture of acylcarnitine standards on a glass slide. The specificity was evaluated by comparing product ion spectra and the precursor ion spectra of 85 m/z of acylcarnitines obtained by the APTDCI method and by electrospray ionization flow injection analysis (ESI-FIA). The method was also employed to analyze acylcarnitines extracted from a pathological dried blood spot and a control. The method enables analysis of biological samples and recognition of some acylcarnitines that are diagnostic markers of inherited metabolic diseases. The intrinsic high-throughput analysis of the ambient desorption ionization methods offers a new opportunity either for its potential application in clinical chemistry and for the expanded screening of some inborn errors of metabolism.     

Super‐atmospheric pressure chemical ionization mass spectrometry

Super‐atmospheric pressure chemical ionization (APCI) mass spectrometry was performed using a commercial mass spectrometer by pressurizing the ion source with compressed air up to 7 atm. Similar to typical APCI source, reactant ions in the experiment were generated with corona discharge using a needle electrode. Although a higher needle potential was necessary to initiate the corona discharge, discharge current and detected ion signal were stable at all tested pressures. A Roots booster pump with variable pumping speed was installed between the evacuation port of the mass spectrometer and the original rough pumps to maintain a same pressure in the first pumping stage of the mass spectrometer regardless of ion source pressure. Measurement of gaseous methamphetamine and research department explosive showed an increase in ion intensity with the ion source pressure until an optimum pressure at around 4–5 atm. Beyond 5 atm, the ion intensity decreased with further increase of pressure, likely due to greater ion losses inside the ion transport capillary. For benzene, it was found that besides molecular ion and protonated species, ion due to [M + 2H]⁺ which was not so common in APCI, was also observed with high ion abundance under super‐atmospheric pressure condition. Copyright © 2013 John Wiley & Sons, Ltd.     

High-throughput assay of rotenone in olive oil using atmospheric pressure chemical ionization tandem mass spectrometry

A high-throughput method is presented for the determination of rotenone in contaminated matrices. The procedure involves atmospheric pressure chemical ionization tandem mass spectrometry with a triple-quadrupole instrument and the use as internal standard of a cycloadduct derivative of rotenone itself. The method was applied to the evaluation of the decay of rotenone in olives and olive oil at various times after exposure to the contaminant.     

Comparison of electrospray ionization,atmospheric pressure chemical ionization and atmospheric pressure photoionization for determining estrogenic chemicals in water by liquid chromatography tandem mass spectrometry with chemical derivatizations

This study compared the sensitivities and matrix effects of four ionization modes and four reversed-phase liquid chromatographic (LC) systems on analyzing estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2), 4-nonylphenol (NP), 4-tert-octylphenol (OP), bisphenol A (BPA) and their derivatives of dansyl chloride or pentafluorobenzyl bromide (PFBBr) in water matrixes using a triple-quadrupole mass spectrometer with selected reaction monitoring (SRM). The four probes were electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI) and APCI/APPI; the four LC systems were ultra-performance liquid chromatography (UPLC) with or without post-column split, a mixed-mode column and two-dimensional LC (2D-LC). Dansylated compounds with ESI at UPLC condition had the most intense signals and less matrix effects of the various combinations of ionization and LC systems. The on-column limits of detection (LODs) of dansylated estrogens by SRM were 0.05–0.20 pg, and the LODs in sewage treatment plant effluent and in river water were 0.23–0.52 and 0.56–0.91 ng/L, respectively. The LODs using selected ion monitoring (SIM) reached low ng/L levels in real samples and measured concentrations were comparable with those of SRM.     

Fragmentation study of simvastatin and lovastatin using electrospray ionization tandem mass spectrometry

The fragmentation mechanism of simvastatin and lovastatin was investigated using both triple quadrupole and ion trap mass spectrometers. The elimination of the ester side-chain followed by dehydration and dissociation of the lactone moiety were observed as the main fragmentation pathways for both compounds. Another major fragmentation process was a C==C double-bond facilitated rearrangement. Our tandem mass spectrometric (MS/MS) data suggested that the beta-hydroxy group was involved in the fragmentation by interacting with the carboxyl group generated from the ring opening of the lactone. As a result, a facile neutral loss of 60 Da (CH(3)COOH or a combination of CH(2)==C==O and H(2)O) was detected. MS/MS studies of the structural analogs also provided evidence that the dehydration of the beta-hydroxy lactone generated preferentially the beta,gamma-unsaturated lactones.     

Chloride-enhanced atmospheric pressure chemical ionization mass spectrometry of polychlorinated n-alkanes

The use of high-performance liquid chromatography combined with chloride-enhanced atmospheric pressure chemical ionization for the determination of polychlorinated n-alkanes (PCAs, also called chlorinated paraffins or CPs) is described as an alternative to gas chromatographic methods. Atmospheric pressure chemical ionization in the negative ion mode formed exclusively [M+Cl](-) adduct ions and suppressed fragmentation when a chlorinated solvent was added. Limits of detection were 1-2 ng/microL for technical PCA mixtures. Response factors for single short-chain PCA homologues with different degrees of chlorination varied by not more than a factor of 6.5. The developed method was applied for the determination of the composition of technical PCA mixtures as well as for the analysis of PCAs in household commodities. Medium-chain PCAs were found in paint samples at concentrations of 8.2-11.5% (w/w), compared with 7.4-11.5% obtained by gas chromatography combined with electron ionization tandem mass spectrometry.     

Determination of selected sulfonamide antibiotics and trimethoprim in manure by electrospray and atmospheric pressure chemical ionization tandem mass spectrometry

A method for the determination of sulfonamides and trimethoprim in the complex matrix liquid manure has been developed using reversed-phase liquid chromatography and atmospheric pressure chemical ionization (APCI) tandem mass spectrometry. A comparison was made between electrospray and atmospheric pressure chemical ionization. APCI proved to be more robust and less sensitive to matrix effects. High-performance liquid chromatographic (HPLC) separation of the analytes was achieved in less than 7 min. The compounds were extracted with ethyl acetate and the extracts were cleaned up by solid-phase extraction on an aminopropyl column. Recoveries were not dependent on the concentration level. The mean recoveries were as follows: trimethoprim 79.0%, sulfadiazine 80.5%, N(4)-acetylsulfadiazine 91.0%, sulfamerazine 78.6%, sulfadimidine 77.2% and sulfamethoxazole 82.8%. Linearity was established over a concentration range of 5 to 5000 microg/kg with correlation coefficients greater than 0.99. The method had a limit of quantitation (LOQ) of 5 microg/kg manure.     

Analysis of hydroxylated polybrominated diphenyl ether metabolites by liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

Hydroxylated polybrominated diphenyl ether (OH‐PBDEs) metabolites have the potential to cause endocrine disruption as well as other health effects. Currently, gas chromatography/mass spectrometry (GC/MS) after derivatization is used for the analysis of OH‐PBDEs. However, there is a need for the direct analysis of OH‐PBDEs at relatively low concentrations in environmental and biological samples. Liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry (LC/APCI‐MS/MS) was evaluated for the analysis of nine OH‐PBDEs, ranging from tri‐ to hexabrominated. Separation of the nine isomeric metabolites was achieved with reversed‐phase liquid chromatography, followed by detection by APCI‐MS in negative mode. Notably, a significant decrease in ionization was observed in 6‐hydroxyl‐substituted PBDE metabolites in the presence of an ortho‐substituted bromine, relative to the other hydroxylated metabolites. This is probably due to the formation of dioxins in the source as a result of the high‐temperature conditions, which prevented ionization by hydrogen abstraction. The MS/MS experiments also provided evidence of the neutral losses of HBr and Br₂, indicating the possible use of neutral loss scanning and selected reaction monitoring (SRM) for the screening of brominated metabolites in samples. The applicability of LC/APCI‐MS/MS was demonstrated for the analysis of metabolites of BDEs 47 and 99 formed in human liver microsomes. The LC/APCI‐MS/MS method was able to detect metabolites that had previously been identified by GC/MS following derivatization. Copyright © 2010 John Wiley & Sons, Ltd.     

Structural characterization and isomer differentiation of chalcones by electrospray ionization tandem mass spectrometry

A series of chalcones were characterized by electrospray ionization tandem mass spectrometry (MS(n)). Several ionization modes were evaluated, including protonation, deprotonation and metal complexation, with metal complexation being the most efficient. Collision-activated dissociation (CAD) was used to characterize the structures, and losses commonly observed include H(2), H(2)O, CO and CO(2), in addition to methyl radicals for the methoxy-containing chalcones. CAD of the metal complexes, especially [Co(II) (chalcone-H) 2,2'-bipyridine](+), allowed the most effective differentiation of the isomeric chalcones with several diagnostic fragment ions appearing upon activation of the metal complexes. MS(n) experiments were performed to support identification of some fragment ions and to verify the proposed fragmentation pathways. In several cases, MS(n) indicated that specific neutral losses occurred by stepwise pathways, such as the neutral loss of 44 u as CH3* and HCO*, or CH(4) and CO, in addition to CO(2).     

Identification and determination of glycosides in tobacco leaves by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry

HPLC-atmospheric pressure chemical ionization MS (HPLC-APCI-MS) was used to screen and identify glycosides in tobacco leaf. MS/MS and MS3 and photodiode array (PDA) detection were also used in the characterization. A total of 12 glycosides were found and four of them were identified based on their abundant [M + H]+ ions, UV spectra, and MS/MS analysis and they are scopolin, rutin, quercetin-3-glycoside, and kaempferol-3-rutinoside. Analytical characteristics of the method were investigated. The contents of these glycosides were obtained and compared based on the relative peak area to the internal standard in seven kinds of tobacco leaf.