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Chemical Ionization (chemical + ionization)
Kinds of Chemical Ionization Terms modified by Chemical Ionization Selected AbstractsA simplified method for HPLC-MS analysis of sterols in vegetable oilEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 12 2008Antonio Segura Carretero Abstract We have developed a liquid-chromatographic method using atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) detection in positive mode. This method was used to separate and identify 15,sterols and 2,dihydroxy triterpenes in saponified oils, enabling the analysis of these compounds directly from saponified samples without recourse to thin-layer chromatography; this fact thus significantly simplifies the process. The analyses were made using a Waters Atlantis 5,µm dC18 150×2.1,mm column with a gradient of acetonitrile/water (0.01% acetic acid) at a flow rate of 0.5,mL/min and a column temperature of 30,°C. The quantification of several of these compounds in soybean oil, palm oil, seed oil, sunflower oil, olive-pomace oil and virgin olive oil was carried out using their commercial standards, and the results were compared satisfactorily with the official method. [source] Indirect identification of isoprenoid quinones in Escherichia coli by LC-MS with atmospheric pressure chemical ionization in negative modeJOURNAL OF BASIC MICROBIOLOGY, Issue 6 2004Mengchun Gao Dr. A novel analytical method was applied for identification of isoprenoid quinones in Escherichia coli by liquid chromatography atmospheric press chemical ionization mass spectrometry in negative mode (LC-NI-APCI-MS). Extraction and clean-up of sample were carried out on Sep-Pak Plus Silica solid-phase extraction cartridges. Ubiquinone-7 (UQ-7), Ubiquinone-8 (UQ-8) and Mequinone-8 (MK-8) were determined directly using combined information on retention time, molecular ion mass, fragment ion masses and UV characteristic spectrometry without any standard reagent. It was found that UQ-8 was the major component of isoprenoid quinones in Escherichia coli under aerobic condition. Compared with UQ-8, the relative abundance of UQ-7 and MK-8 is only 15% and 14%, respectively. The average recoveries of UQ-6, UQ-10 and vitamin K1 in Escherichia coli were investigated by standard spiking experiment. The recoveries were achieved in the range from 94 to 106%, and the relative standard deviations (RSD) of the triplicate analysis of the spiked samples (UQ-6, UQ-10 and vitamin K1) ranged from 3 to 8%. The detection limits of LC-NI-APCI-MS were estimated to be 5, 40 and 0.8 ,g/g dry cell for UQ-6, UQ-10 and vitamin K1, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Development of ambient sampling chemi/chemical ion source with dielectric barrier dischargeJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 8 2010Lee Chuin Chen Abstract The development of a new configuration of chemical ionization (CI)-based ion source is presented. The ambient air containing the gaseous sample is sniffed into an enclosed ionization chamber which is of sub-ambient pressure, and is subsequently mixed with metastable species in front of the ion inlet of the mass spectrometer. Metastable helium atoms (He*) are used in this study as the primary ionizing agents and are generated from a dielectric barrier discharge (DBD) source. The DBD is powered by an AC high-voltage supply and the configuration of the electrodes is in such a way that the generated plasma is confined within the discharge tube and is not extended into the ionization chamber. The construction of the ion source is simple, and volatile compounds released from the bulky sample can also be analyzed directly by approaching the sample to the sampling nozzle. When combined with heated nitrogen or other desorption methods, its application can also be extended to non-volatile compounds, and the consumption for helium can be kept minimum solely for maintaining the stable discharge and gas phase ionization. Applications to non-proximate sample analysis, direct determination of active ingredients in drug tablets and the detection of trace explosive such as hexamethylene triperoxide diamine are demonstrated. Copyright © 2010 John Wiley & Sons, Ltd. [source] Dimerization of ionized 4-(methyl mercapto)-phenol during ESI, APCI and APPI mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2009Lianming Wu Abstract A novel ion/molecule reaction was observed to occur under electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photo ionization (APPI) conditions, leading to dimerization of ionized 4-(methyl mercapto)-phenol followed by fast H· loss. The reaction is particularly favored during ESI, which suggests that this ion/molecule reaction can occur both in the solution inside the ESI-charged droplets and in the gas-phase environment of most other atmospheric pressure ionization techniques. The dimerization reaction is inherent to the electrolytic process during ESI, whereas it is more by ion/molecule chemistry in nature during APCI and APPI. From the tandem mass spectrometry (MS/MS) data, accurate mass measurements, hydrogen/deuterium (H/D) exchange experiments and density functional theory (DFT) calculations, two methyl sulfonium ions appear to be the most likely products of this electrophilic aromatic substitution reaction. The possible occurrence of this unexpected reaction complicates mass spectral data interpretation and can be misleading in terms of structural assignment as reported herein for 4-(methyl mercapto)-phenol. Copyright © 2009 John Wiley & Sons, Ltd. [source] Introduction of HPLC/orbitrap mass spectrometry as screening method for doping controlJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2008E. D. Virus Abstract A new doping control screening method has been developed, for the analysis of doping agents in human urine, using HPLC/orbitrap with in-source collision-induced dissociation and atmospheric pressure chemical ionization. The developed method allows the detection of 29 compounds, including agents with antiestrogenic activity, ,2 agonists, exogenous anabolic steroids, and other anabolic agents. The mass accuracy of this method is better at 2 ppm using an external reference. The detection limit for all compounds tested was better than 100 pg/ml. The recoveries of most analytes were above 70%. The measured median repeatability values for doping agents included in the method at concentrations of 1 and 10 ng/ml were 21 and 17%, respectively. The relative standard deviation (RSD) of the intraday precision (n = 6) ranged from RSD = 16,22%, whereas the interday precision (n = 18), ranged from RSD = 17,26%, depending on the solute concentration investigated. Copyright © 2008 John Wiley & Sons, Ltd. [source] Optimization of the ESI and APCI experimental variables for the LC/MS determination of s-triazines, methylcarbamates, organophosphorous, benzimidazoles, carboxamide and phenylurea compounds in orange samplesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2007Guilherme M. Titato Abstract In this work, ten selected pesticides of different chemical groups, indicated to orange culture, were extracted and determined by liquid chromatography,mass spectrometry using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) operating in the positive ion detection mode. Applying a variables selection technique verified that cone voltage, source temperature and drying-gas flow-rate are the critical variables when the ESI was used, while cone voltage was found to be the only critical variable for the MS system, operating with the APCI ionization mode. After optimization of the most important parameters through the variables selection technique, the selected ion-recording (SIR) mode, monitoring the [M + H]+ species for all the compounds, was applied for the method validation of the pesticides, in both ionization modes. In orange samples, matrix effects did not interfere with the determination of the pesticides. Pesticides quantification limits ranged from 10 to 50 µg kg,1 for ESI and from 8.2 to 45 µg kg,1 for APCI. Linearity was studied from LOQ upto 200 times LOQ values (r > 0.98). Recoveries obtained were in the range of 70.2,100.5% (RSDs less than 10%). In order to guarantee that the identification and confirmation of the studied pesticides in real samples were unequivocal, characteristic fragment ions of the pesticides were obtained by varying the cone voltage (in-source CID). Copyright © 2007 John Wiley & Sons, Ltd. [source] Screening, library-assisted identification and validated quantification of 23 benzodiazepines, flumazenil, zaleplone, zolpidem and zopiclone in plasma by liquid chromatography/mass spectrometry with atmospheric pressure chemical ionizationJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 8 2004Carsten Kratzsch Abstract A liquid chromatographic/mass spectrometric assay with atmospheric pressure chemical ionization (LC/APCI-MS) is presented for fast and reliable screening and identification and also for precise and sensitive quantification in plasma of the 23 benzodiazepines alprazolam, bromazepam, brotizolam, camazepam, chlordiazepoxide, clobazam, clonazepam, diazepam, flunitrazepam, flurazepam, desalkylflurazepam, lorazepam, lormetazepam, medazepam, metaclazepam, midazolam, nitrazepam, nordazepam, oxazepam, prazepam, temazepam and tetrazepam, triazolam, their antagonist flumazenil and the benzodiazepine BZ1 (omega 1) receptor agonists zaleplone, zolpidem and zopiclone. It allows confirmation of the diagnosis of an overdose situation and monitoring of psychiatric patients' compliance. The analytes were isolated from plasma using liquid,liquid extraction and were separated on a Merck LiChroCART column with Superspher 60 RP Select B as the stationary phase. Gradient elution was performed using aqueous ammonium formate and acetonitrile. After screening and identification in the scan mode using the authors' LC/MS library, the analytes were quantified in the selected-ion monitoring mode. The quantification assay was fully validated. It was found to be selective proved to be linear from sub-therapeutic to over therapeutic concentrations for all analytes, except bromazepam. The corresponding reference levels the assay's accuracy and precision data for all studied substances are listed. The accuracy and precision data were within the required limits with the exception of those for bromazepam. The analytes were stable in frozen plasma for at least 1 month. The validated assay was successfully applied to several authentic plasma samples from patients treated or intoxicated with various benzodiazepines or with zaleplone, zolpidem or zopiclone. It has proven to be appropriate for the isolation, separation, screening, identification and quantification of the drugs mentioned above in plasma for clinical toxicology, e.g. in cases of poisoning, and forensic toxicology, e.g. in cases of driving under the influence of drugs. Copyright © 2004 John Wiley & Sons, Ltd. [source] Direct-temperature mass spectrometric detection of volatile terpenoids and natural terpenoid polymersin fresh and artificially aged resinsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2003Dominique Scalarone Abstract Electron impact (EI) ionization and ammonia chemical ionization (NH3/CI) direct-temperature mass spectrometry (DTMS) was used to characterize five natural terpenoid resins: dammar, mastic, colophony, Manila copal and sandarac. Compositional differences were highlighted by the identification of low molecular mass compounds, ranging from di- to triterpenoids, and polymeric components, based on polycadinene and polycommunic acid. Photo-ageing processes occurring under accelerated indoor and outdoor exposure conditions were also investigated. NH3/CI and tetramethylammonium hydroxide EI were applied to increase the sensitivity towards highly oxidized molecules. Oxidation and cross-linking reactions were found to affect mostly triterpenoid resins and diterpenoid abietane and pimarane molecules. Oxidation proceeds through a radical mechanism, generally starting from conjugated double bonds. Oxygen atoms are incorporated in the terpenoid structures in the form of alcohols, ketones and carboxylic acids. Oxidized cadinene oligomers released by pyrolytic degradation of the polycadinene fraction of dammar were detected even in unaged samples. Evidence is given indicating the occurrence of cleavages in the cross-linked polycommunic structure of aged sandarac and Manila copal. Bond scissions produce oligomeric fragments based on the communic acid structure and sufficiently volatile to be desorbed at low temperature in DTMS measurements. Copyright © 2003 John Wiley & Sons, Ltd. [source] Determination of 17,-estradiol in bovine plasma: development of a highly sensitive technique by ion trap gas chromatography,tandem mass spectrometry using negative chemical ionization,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2002Giancarlo Biancotto Abstract A novel approach to the determination of 17,-estradiol in bovine plasma is presented. The observed enhanced sensitivity is gained by the application of tandem mass spectrometry (MS) fragmentation to a stable, well characterized negative ion produced by chemical ionization (methane as reagent gas). A specific derivatizing reactant is employed (pentafluorobenzyl bromide), combined with bis-trimethylsilyltrifluoroacetamide, to favor the formation of a diagnostic precursor negative ion. Plasma samples are purified through a C18 solid phase extraction column and derivatized before gas chromatography,MS analysis. The accuracy and the precision of the method, tested over a set of spiked samples, were satisfactory. The limit of detection was found to be 5 pg ml,1 and the limit of quantification was fixed at 20 pg ml,1. The fragmentation pattern is fully explained and the method is applicable for the official analysis of bovine plasma for the detection of 17,-estradiol according to the European criteria 256/93 and to the draft SANCO/1805/2000 rev. 3. The quantification of incurred positive samples was performed according to the proposed procedure and compared with the results obtained by standardized radio immuno assay; the estimated concentrations were significantly similar. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of eluent on the ionization efficiency of flavonoids by ion spray, atmospheric pressure chemical ionization, and atmospheric pressure photoionization mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2001Jussi-Pekka Rauha Abstract The effect of nine different eluent compositions on the ionization efficiency of five flavonoids was studied using ion spray (IS), atmospheric pressure chemical ionization (APCI), and the novel atmospheric pressure photoionization (APPI), in positive and negative ion modes. The eluent composition had a great effect on the ionization efficiency, and the optimal ionization conditions were achieved in positive ion IS and APCI using 0.4% formic acid (pH 2.3) as a buffer, and in negative ion IS and APCI using ammonium acetate buffer adjusted to pH 4.0. For APPI work, the eluent of choice appeared to be a mixture of organic solvent and 5 mM aqueous ammonium acetate. The limits of detection (LODs) were determined in scan mode for the analytes by liquid chromatography/mass spectrometry using IS, APCI and APPI interfaces. The results show that negative ion IS with an eluent system consisting of acidic ammonium acetate buffer provides the best conditions for detection of flavonoids in mass spectrometry mode, their LODs being between 0.8 and 13 µM for an injection volume of 20 µl. Copyright © 2001 John Wiley & Sons, Ltd. [source] Reactions of gaseous ions.JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2001Editor's Note: The following paper is the first in a series that describes the gas phase reactions of positive ions derived from compounds such as methane and ethylene with other gas phase molecules to produce secondary ions. These very careful experiments formed the basis of chemical ionization, one of the ionization techniques that revolutionized mass spectrometry at that time and a technique still very much in use today. At elevated pressures in a mass spectrometer ion source reactions occur between certain ions and the neutral species present. We have studied the various secondary ions formed in methane and ethylene at elevated pressures and have determined the reactions by which they are formed and the rates of these reactions. The rates are all extremely fast. The reaction rates have been treated by classical collision theory and it has been shown that to a fair approximation the cross-sections and reaction rate constants can be predicted from a simple balance of rotational and polarization forces. [Reprinted from J. Am. Chem. Soc. 1957; 79: 2419.] Copyright © 1957 by the American Chemical Society and reprinted by permission of the copyright owner. [source] Simultaneous characterization of isoflavonoids and astragalosides in two Astragalus species by high-performance liquid chromatography coupled with atmospheric pressure chemical ionization tandem mass spectrometryJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2007Xi Zhang Abstract A method was developed for the simultaneous identification of astragalosides (AGs) and isoflavonoids (IFs) in the roots of Astragalus membranaceus and Astragalus mongholicus by HPLC coupled with atmospheric pressure chemical ionization MS/MS (HPLC-APCI-MS/MS). Diagnostic fragment ions of AGs and different group of IFs were obtained with one AG and eight IF standards analyzed by CID-MS, which were adopted as characteristic MS/MS fingerprints for further identification of these compounds in the two Astragalus species by using HPLC-APCI-MS/MS. A total of 20 IFs and 10 AGs were identified or tentatively identified. Among them, six IFs were detected in A. membranaceus for the first time and five IFs were firstly identified in A. mongholicus. The results indicate that HPLC-APCI-MS/MS is a powerful tool for the simultaneous characterization of IFs and AGs in complex matrix. [source] Characterization via liquid chromatography coupled to diode array detector and tandem mass spectrometry of supercritical fluid antioxidant extracts of Spirulina platensis microalgaJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9-10 2005Jose A. Mendiola Abstract Spirulina platensis microalga has been extracted on a pilot scale plant using supercritical fluid extraction (SFE) under various extraction conditions. The extraction yield and the antioxidant activity of the extracts were evaluated in order to select those extracts with both the highest antioxidant capacity and a good extraction yield. These extracts were characterized using LC coupled to diode array detection (DAD) and LC coupled to mass spectrometry (MS) with two different interfaces, atmospheric pressure chemical ionization (APCI) and electrospray (ESI) which allowed us to perform tandem MS by using an ion trap analyzer. The best extraction conditions were as follows: CO2 with 10% of modifier (ethanol) as extraction solvent, 55°C (extraction temperature) and 220 bar (extraction pressure). Fractionation was achieved by cascade depressurization providing two extracts with different activity and chemical composition. Several compounds have been identified in the extracts, corresponding to different carotenoids previously identified in Spirulina platensis microalga along with chlorophyll a and some degradation products. Also, the structure of some phenolic compounds could be tentatively identified. The antioxidant activity of the extracts could be attributed to some of the above mentioned compounds. [source] Matrix effects in quantitative pesticide analysis using liquid chromatography,mass spectrometryMASS SPECTROMETRY REVIEWS, Issue 6 2006W.M.A. Niessen Abstract Combined liquid chromatography,mass spectrometry using electrospray or atmospheric-pressure chemical ionization has become an important tool in the quantitative analysis of pesticide residues in various matrices in relation to environmental analysis, food safety, and biological exposure monitoring. One of the major problems in the quantitative analysis using LC,MS is that compound and matrix-dependent response suppression or enhancement may occur, the so-called matrix effect. This article reviews issues related to matrix effects, focusing on quantitative pesticide analysis, but also paying attention to expertise with respect to matrix effects acquired in other application areas of LC,MS, especially quantitative bioanalysis in the course of drug development. © 2006 Wiley Periodicals, Inc. [source] Selected ion flow tube mass spectrometry (SIFT-MS) for on-line trace gas analysisMASS SPECTROMETRY REVIEWS, Issue 5 2005David Smith Abstract Selected ion flow tube mass spectrometry (SIFT-MS) is a new analytical technique for the real-time quantification of several trace gases simultaneously in air and breath. It relies on chemical ionization of the trace gas molecules in air/breath samples introduced into helium carrier gas using H3O+, NO+, and O precursor ions. Reactions between the precursor ions and trace gas molecules proceed for an accurately defined time, the precursor and product ions being detected and counted by a downstream mass spectrometer, thus effecting quantification. Absolute concentrations of trace gases in single breath exhalation can be determined by SIFT-MS down to ppb levels, obviating sample collection and calibration. Illustrative examples of SIFT-MS studies include (i) analysis of gases from combustion engines, animals and their waste, and food; (ii) breath and urinary headspace studies of metabolites, ethanol metabolism, elevated acetone during ovulation, and exogenous compounds; and (iii) urinary infection and the presence of tumors, the influence of dialysis on breath ammonia, acetone, and isoprene, and acetaldehyde released by cancer cells in vitro. Flowing afterglow mass spectrometry (FA-MS) is briefly described, which allows on-line quantification of deuterium in breath water vapor. © 2004 Wiley Periodicals, Inc., Mass Spec Rev 24:661,700, 2005 [source] Gas-phase formation of protonated benzene during collision-induced dissociation of certain protonated mono-substituted aromatic molecules produced in electrospray ionizationRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2010Min Li Protonated benzene, C6H, has been studied extensively to understand the structure and energy of a protonated organic molecule in the gas phase. The formation of C6H is either through direct protonation of benzene, i.e., chemical ionization, or through fragmentation of certain radical cations produced from electron ionization or photon ionization. We report a novel observation of C6H as a product ion formed in the collision-induced dissociation (CID) of protonated benzamide and related molecules produced via electrospray ionization (ESI). The formation of C6H from these even-electron precursor ions during the CID process, which has not been previously reported, is proposed to occur from the protonated molecules via a proton migration in a five-membered ring intermediate followed by the cleavage of the mono-substituent CC bond and concurrent formation of an ion-molecule complex. This unique mechanism has been scrutinized by examining some deuterated molecules and a series of structurally related model compounds. This finding provides a convenient mean to generate C6H, a reactive intermediate of considerable interest, for further physical or chemical investigation. Further studies indicate that the occurrence of C6H in liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) appears to be a rather common phenomenon for many compounds that contain ,benzoyl-type' moieties. Hence, the observation of the C6H ion in LC/ESI-MS/MS can be used as an informative fragmentation pathway which should facilitate the identification of a great number of compounds containing the ,benzoyl-type' and similar structural features. These compounds are frequently present in food and pharmaceutical products as leachable impurities that require strict control and rapid elucidation of their identities. Copyright © 2010 John Wiley & Sons, Ltd. [source] Systematic investigation of ion suppression and enhancement effects of fourteen stable-isotope-labeled internal standards by their native analogues using atmospheric-pressure chemical ionization and electrospray ionization and the relevance for multi-analyte liquid chromatographic/mass spectrometric proceduresRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2010Daniela Remane In clinical and forensic toxicology, multi-analyte procedures are very useful to quantify drugs and poisons of different classes in one run. For liquid chromatographic/tandem mass spectrometric (LC/MS/MS) multi-analyte procedures, often only a limited number of stable-isotope-labeled internal standards (SIL-ISs) are available. If an SIL-IS is used for quantification of other analytes, it must be excluded that the co-eluting native analyte influences its ionization. Therefore, the effect of ion suppression and enhancement of fourteen SIL-ISs caused by their native analogues has been studied. It could be shown that the native analyte concentration influenced the extent of ion suppression and enhancement effects leading to more suppression with increasing analyte concentration especially when electrospray ionization (ESI) was used. Using atmospheric-pressure chemical ionization (APCI), methanolic solution showed mainly enhancement effects, whereas no ion suppression and enhancement effect, with one exception, occurred when plasma extracts were used under these conditions. Such differences were not observed using ESI. With ESI, eleven SIL-ISs showed relevant suppression effects, but only one analyte showed suppression effects when APCI was used. The presented study showed that ion suppression and enhancement tests using matrix-based samples of different sources are essential for the selection of ISs, particularly if used for several analytes to avoid incorrect quantification. In conclusion, only SIL-ISs should be selected for which no suppression and enhancement effects can be observed. If not enough ISs are free of ionization interferences, a different ionization technique should be considered. Copyright © 2010 John Wiley & Sons, Ltd. [source] Gas chromatography coupled to electron capture negative ion mass spectrometry with nitrogen as the reagent gas , an alternative method for the determination of polybrominated compoundsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2009Natalie Rosenfelder Gas chromatography in combination with electron capture negative ion mass spectrometry (GC/ECNI-MS) is a sensitive method for the determination of polybrominated compounds in environmental and food samples via detection of the bromide ion isotopes m/z 79 and 81. The standard reagent gas for inducing chemical ionization in GC/ECNI-MS is methane. However, the use of methane has some drawbacks as it promotes carbonization of the filament and ion source. In this study, we explored the suitability of nitrogen as reagent gas for the determination of brominated flame retardants (polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs), allyl-2,4,6-tribromophenyl ether (ATE) and 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE)) and halogenated natural products (for instance, methoxylated tetrabrominated diphenylethers and polybrominated hexahydroxanthene derivatives). An ion source temperature of 250°C and a nitrogen pressure of 7 Torr in the ion source gave the highest response for m/z 79 and 81 of virtually all investigated polybrominated compounds. Using these conditions, nitrogen-mediated GC/ECNI-MS usually gave higher sensitivity than the method with methane previously used in our lab. In addition, the ion source was not contaminated to the same degree and the lifetime of the filament was significantly increased. Moreover, the response factors of the different polybrominated compounds with the exception of 2,4,6-tribromophenol were more uniform than with methane. Nitrogen is available at very high purity at relatively low price. Copyright © 2009 John Wiley & Sons, Ltd. [source] Drug impurity profiling by capillary electrophoresis/mass spectrometry using various ionization techniquesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2009Paul Hommerson Capillary electrophoresis/mass spectrometry (CE/MS) is predominantly carried out using electrospray ionization (ESI). Recently, atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) have become available for CE/MS. With the VUV lamp turned off, the APPI source may also be used for CE/MS by thermospray ionization (TSI). In the present study the suitability of ESI, APCI, APPI and TSI for drug impurity profiling by CE/MS in the positive ion mode is evaluated. The drugs carbachol, lidocaine and proguanil and their potential impurities were used as test compounds, representing different molecular polarities. A background electrolyte of 100,mM acetic acid (pH 4.5) provided baseline separation of nearly all impurities from the respective drugs. APPI yielded both even- and odd-electron ions, whereas the other ionization techniques produced even-electron ions only. In-source fragmentation was more pronounced with APCI and APPI than with ESI and TSI, which was most obvious for proguanil and its impurities. In general, ESI and TSI appeared the most efficient ionization techniques for impurities that are charged in solution achieving detection limits of 100,ng/mL (full-scan mode). APPI and APCI showed a lower efficiency, but allowed ionization of low and high polarity analytes, although quaternary ammonium compounds (e.g. carbachol) could not be detected. Largely neutral compounds, such as the lidocaine impurity 2,6-dimethylaniline, could not be detected by TSI, and yielded similar detection limits (500,ng/mL) for ESI, APPI and APCI. In many cases, impurity detection at the 0.1% (w/w) level was possible when 1,mg/mL of parent drug was injected with at least one of the CE/MS systems. Overall, the tested CE/MS systems provide complementary information as illustrated by the detection and identification of an unknown impurity in carbachol. Copyright © 2009 John Wiley & Sons, Ltd. [source] Identification of organic hydroperoxides and hydroperoxy acids in secondary organic aerosol formed during the ozonolysis of different monoterpenes and sesquiterpenes by on-line analysis using atmospheric pressure chemical ionization ion trap mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2009Marc-Christopher Reinnig On-line ion trap mass spectrometry (ITMS) enables the real-time characterization of reaction products of secondary organic aerosol (SOA). The analysis was conducted by directly introducing the aerosol particles into the ion source. Positive-ion chemical ionization at atmospheric pressure (APCI(+)) ITMS was used for the characterization of constituents of biogenic SOA produced in reaction-chamber experiments. APCI in the positive-ion mode usually enables the detection of [M+H]+ ions of the individual SOA components. In this paper the identification of organic peroxides from biogenic volatile organic compounds (VOCs) by on-line APCI-ITMS is presented. Organic peroxides containing a hydroperoxy group, generated by gas-phase ozonolysis of monoterpenes (, -pinene and , -pinene) and sesquiterpenes (, -cedrene and , -copaene), could be detected via on-line APCI(+)-MS/MS experiments. A characteristic neutral loss of 34,Da (hydrogen peroxide, H2O2) in the on-line MS/MS spectra is a clear indication for the existence of an organic peroxide, containing a hydroperoxy functional group. Copyright © 2009 John Wiley & Sons, Ltd. [source] Analysis of oligomeric peroxides in synthetic triacetone triperoxide samples by tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 3 2009Michael E. Sigman Oligomeric peroxides formed in the synthesis of triacetone triperoxide (TATP) have been analyzed by mass spectrometry utilizing both electrospray ionization (ESI) and chemical ionization (CI) to form sodiated adducts (by ESI) and ammonium adducts (by CI and ESI). Tandem mass spectrometry and deuterium isotopic labeling experiments have been used to elucidate the collision-induced dissociation (CID) mechanisms for the adducts. The CID mechanisms differ for the sodium and ammonium adducts and vary with the size of the oligoperoxide. The sodium adducts of the oligoperoxides, H[OOC(CH3)2]nOOH, do not cyclize under CID, whereas the ammonium adducts of the smaller oligoperoides (n,<,6) do form the cyclic peroxides under CID. Larger oligoperoxide adducts with both sodium and ammonium undergo dissociation through cleavage of the backbone under CID to form acyl- and hydroperoxy-terminated oligomers of the general form CH3C(O)[OOC(CH3)2]xOOH, where x is an integer less than the original oligoperoxide degree of oligomerization. The oligoperoxide distribution is shown to vary batch-to-batch in the synthesis of TATP and the post-blast distribution differs slightly from the distribution in the uninitiated material. The oligoperoxides are shown to be decomposed under gentle heating. Copyright © 2009 John Wiley & Sons, Ltd. [source] Precursor ion scan profiles of acylcarnitines by atmospheric pressure thermal desorption chemical ionization tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2008Giuseppe Paglia 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,µL 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. Copyright © 2008 John Wiley & Sons, Ltd. [source] Microsynthesis and mass spectral study of Chemical Weapons Convention related 2-alkyl-1,3,6,2-dioxathiaphosphocane-2-oxidesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2008Meehir Palit Chemical Weapons Convention (CWC)-related compounds where the phosphorus atom is part of a ring have very limited representation in mass spectral libraries and the open literature. Here we report electron ionization (EI), chemical ionization (CI) and electrospray ionization tandem mass spectrometry (ESI-MSn) spectra and retention indices for 2-alkyl-1,3,6,2-dioxathiaphosphocane-2-oxides (alkyl C1 to C3) which are new cyclic chemicals covered under the CWC. The EI mass spectra show a pattern of ion fragmentation that is similar to that of other cyclic phosphonates in that loss of the alkylphosphonic acid as a neutral loss is more important than the presence of the protonated alkylphosphonic acid. In contrast to other cyclic phosphonates, the 2-alkyl-1,3,6,2-dioxathiaphosphocane-2-oxides show almost no protonated alkylphosphonic acid and as a result the spectra do not carry the same distinctive signature of the phosphorus,carbon bond that is required for the chemical to be covered under the CWC. Copyright © 2008 John Wiley & Sons, Ltd. [source] Mass spectrometry in the characterization of ambers.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2008Amber is a fossil resin constituted of organic polymers derived through complex maturation processes of the original plant resin. A classification of eight samples of amber of different geological age (Miocene to Triassic) and geographical origin is here proposed using direct mass spectrometric techniques, i.e. laser desorption ionization (LDI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), in order to obtain a fingerprint related to the amber origin. Differences and similarities were detected among the spectra with the four methods, showing quite complex spectra, full of ionic species in the mass range investigated (up to m/z 2000). The evaluation required statistical analysis involving multivariate techniques. Cluster analysis or principal component analysis (PCA) generally did not show a clear clustering with respect to the age of samples, except for the APPI method, which allowed a satisfying clustering. Using the total ion current (TIC) obtained by the different analytical approaches on equal quantities of the different amber samples and plotted against the age, the only significant correlation appeared to be that involving APPI. To validate the method, four amber samples from Cretaceous of Spain were analyzed. Also in this case a significant correlation with age was found only with APPI data. PCA obtained with TIC values from all the MS methods showed a fair grouping of samples, according to their age. Three main clusters could be detected, belonging to younger, intermediate and older fossil resins, respectively. This MS analysis on crude amber, either solid or extract, followed by appropriate multivariate statistical evaluation, can provide useful information on amber age. The best results are those obtained by APPI, indicating that the quantity of amber soluble components that can be photoionized decreases with increasing age, in agreement with the formation of highly stable, insoluble polymers. Copyright © 2008 John Wiley & Sons, Ltd. [source] Surface-activated chemical ionization and high-flow gradient chromatography to reduce matrix effectRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2006Simone Cristoni The new atmospheric pressure chemical ionization source, named surface-activated chemical ionization (SACI), has been used in conjunction with high-flow gradient chromatography to reduce the matrix effect. This high-flow gradient chromatography approach avoids the co-elution of analyte and biological matrix compounds that leads to a reduction in quantitation errors due to matrix effect. However, this approach cannot be employed with the classical electrospray ionization (ESI) source that usually works at low eluent flow (<,300,µL/min). SACI can work at high eluent flow (100,2000,µL/min) and can be employed in conjunction with high-flow gradient chromatography. The reduction in matrix effect in tacrolimus analysis in protein-precipitated blood samples, an important immunosuppressive agent for renal transplantation, is presented and discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] Development and validation of a liquid chromatographic/tandem mass spectrometric method for the determination of sertraline in human plasmaRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2006Xiaoyan Chen A sensitive and rapid liquid chromatographic/tandem mass spectrometric method was developed and validated for the determination of sertraline in human plasma. The analyte and internal standard (IS, diphenhydramine) were extracted with 3,mL of diethyl ether/dichloromethane (2:1, v/v) from 0.25,mL plasma, then separated on a Zorbax Eclipse XDB C18 column using methanol/water/formic acid (75:25:0.1, v/v/v) as the mobile phase. The triple quadrupole mass spectrometry was applied via an atmospheric pressure chemical ionization (APCI) source for detection. The fragmentation pattern of the protonated sertraline was elucidated with the aid of product mass spectra of isotopologous peaks. Quantification was performed using selected reaction monitoring of the transitions of m/z 306,,,159 for sertraline and m/z 256,,,167 for the IS. The method was linear over the concentration range of 0.10,100,ng/mL. The intra-day and inter-day precisions, expressed by relative standard deviation, were both less than 6.7%. Assay accuracies were within ±6.9% as terms of relative error. The lower limit of quantification (LLOQ) was identifiable and reproducible at 0.10,ng/mL with a precision of 8.3% and an accuracy of 9.6%. The validated method has been successfully applied for the pharmacokinetic study and bioequivalence evaluation of sertraline in 18 healthy volunteers after a single oral administration of 50,mg sertraline hydrochloride tablets. Copyright © 2006 John Wiley & Sons, Ltd. [source] Simultaneous quantitative determination of cyclosporine A and its three main metabolites (AM1, AM4N and AM9) in human blood by liquid chromatography/mass spectrometry using a rapid sample processing methodRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2006Nozomu Koseki We have developed a sensitive and specific liquid chromatography/mass spectrometry (LC/MS) method for the simultaneous determination of cyclosporine A (CsA) and its three main metabolites (AM1, AM4N and AM9) in human blood. Following protein precipitation, supernatant was directly injected into the LC/MS system. Chromatographic separation was accomplished on a Symmetry C8 (4.6,×,75,mm, 3.5,µm) column with a linear gradient elution prior to detection by atmospheric pressure chemical ionization (APCI) MS using selected ion monitoring (SIM) in positive mode. This method can be applied to single mass equipment. The analytical range for each analyte was set at 1,2500,ng/mL using 100,µL of blood sample. The analytical method was fully validated according to FDA guidance. Intra-day mean accuracy and precision were 95.2,113.5% and 0.9,8.9%, respectively. Inter-day mean accuracy and precision were 95.8,107.0% and 1.5,10.7%, respectively. In blood all analytes were stable during three freeze/thaw cycles, for 24,h at room temperature and for 12 months at or below ,15°C. Stability was also confirmed in processed samples for 24,h at 10°C and for 6 months at 4°C in methanol. In addition, we confirmed the method could avoid matrix effects from transplant subjects' samples. This LC/MS technique provided an excellent method for simultaneous quantitative determination of CsA and its three metabolites for evaluation of their pharmacokinetic profiles. Copyright © 2006 John Wiley & Sons, Ltd. [source] Surface-activated chemical ionization versus electrospray ionization in the study of selected aluminium(III)/ligand solution equilibriaRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2006Valerio B. Di Marco No abstract is available for this article. [source] Differentiation of isobaric compounds using chemical ionization reaction mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2005Kevin P. Wyche The technique of proton transfer reaction mass spectrometry (PTR-MS) couples a proton transfer reagent, usually H3O+, with a drift tube and mass spectrometer to determine concentrations of volatile organic compounds. Here we describe a first attempt to use chemical ionization (CI) reagents other than proton transfer species inside a PTR-MS instrument. The ability to switch to other types of CI reagents provides an extra dimension to the technique. This capability is demonstrated by focusing on the ability to distinguish several isobaric aldehydes and ketones, including the atmospherically important molecules methacrolein and methyl vinyl ketone. Two CI reagents were selected, H3O+ and NO+, both being cleanly generated in a low intensity radioactive source prior to injection into the drift tube. By recording spectra with both of these reagents, the contributions from different isobaric molecules can be separated by virtue of their unique spectrometric ,fingerprints'. The work demonstrates that this form of instrumentation is not restricted to proton transfer reagents and is the basis of a more general technique, chemical ionization reaction mass spectrometry (CIRMS). Copyright © 2005 John Wiley & Sons, Ltd. [source] Using a triple-quadrupole mass spectrometer in accurate mass mode and an ion correlation program to identify compounds,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2005Andrew H. Grange Atomic masses and isotopic abundances are independent and complementary properties for discriminating among ion compositions. The number of possible ion compositions is greatly reduced by accurately measuring exact masses of monoisotopic ions and the relative isotopic abundances (RIAs) of the ions greater in mass by +1,Da and +2,Da. When both properties are measured, a mass error limit of 6,10,mDa (<,31,ppm at 320,Da) and an RIA error limit of 10% are generally adequate for determining unique ion compositions for precursor and fragment ions produced from small molecules (less than 320,Da in this study). ,Inherent interferences', i.e., mass peaks seen in the product ion mass spectrum of the monoisotopic [M+H]+ ion of an analyte that are ,2, ,1, +1, or +2,Da different in mass from monoisotopic fragment ion masses, distort measured RIAs. This problem is overcome using an ion correlation program to compare the numbers of atoms of each element in a precursor ion to the sum of those in each fragment ion and its corresponding neutral loss. Synergy occurs when accurate measurement of only one pair of +1,Da and +2,Da RIAs for the precursor ion or a fragment ion rejects all but one possible ion composition for that ion, thereby indirectly rejecting all but one fragment ion-neutral loss combination for other exact masses. A triple-quadrupole mass spectrometer with accurate mass capability, using atmospheric pressure chemical ionization (APCI), was used to measure masses and RIAs of precursor and fragment ions. Nine chemicals were investigated as simulated unknowns. Mass accuracy and RIA accuracy were sufficient to determine unique compositions for all precursor ions and all but two of 40 fragment ions, and the two corresponding neutral losses. Interrogation of the chemical literature provided between one and three possible compounds for each of the nine analytes. This approach for identifying compounds compensates for the lack of commercial ESI and APCI mass spectral libraries, which precludes making tentative identifications based on spectral matches. Published in 2005 by John Wiley & Sons, Ltd. [source] | |||||||||||||