CI Mass Spectra Research Articles

Application of Chemical Ionization in the Analysis of Ethylphosphonic Acid Derivatives.

The microsynthesis of 32 dialkyl derivatives of ethylphosphonic acid and the same number of monoalkyl derivatives was carried out to perform comparative studies using gas chromatography combined with mass spectrometry in chemical ionization mode which is one of the analytical techniques recommended by the Organisation for the Prohibition of Chemical Weapons (OPCW). The huge number of possible representatives makes it difficult to have complete spectral libraries of all substances in this class. Therefore, we decided to synthesize and instrumentally analyze only representatives of the selected series of homologues in this work. The analysis of the obtained results allowed us to find the rules for predicting mass spectra and the factors determining the retention parameters. Symmetrical diesters and monoesters of ethylphosphonic acid were selected for this study. During the conducted experiments using chemical ionization with methane as the reaction gas, protonated analyte molecules with high relative intensities were obtained; in many cases, these are base peaks in the spectrum. The obtained results allow grouping of the synthesized compounds depending on the introduced alkyl substituent. Retention data of the tested analytes were collected during the research by using electron ionization. The retention parameters of the tested compounds from each homologous series were also summarized and compared. Chemical Warfare Agents (CWA) analysis continues to be an important issue, especially in the context of the regular Proficiency Tests organized by the OPCW for identifying chemical compounds that are of interest to the Chemical Weapons Convention. Five compounds were synthesized whose spectra were not available in EI mass spectral libraries, and their retention indices were unknown. The identification of these substances was supported by the CI mass spectra and retention data, using previously developed relationships. Therefore, it is reasonable to conclude that the research method used is useful and effective.

Chemical Characterization and Quantitation of Phenols in Fuel Extracts by Using Gas Chromatography/Methane Chemical Ionization Triple Quadrupole Mass Spectrometry

The ability to detect, characterize, and quantify phenols in aviation fuels is critical as these compounds can negatively affect the storage stability of the fuel. However, some phenols inhibit free-radical autoxidation and hence are beneficial. The development of a method based on gas chromatography coupled with positive-ion-mode methane chemical ionization/triple quadrupole mass spectrometry [GC/(methane CI) QqQ] for the characterization and quantitation of phenols in fuels is reported here. Sixteen phenols, ranging from phenol to phenols with up to three alkyl groups of different chain lengths, were studied. Natural phenols (defined as phenols without tert-butyl groups) were protonated upon methane CI, which was associated with diagnostic fragmentation. For example, upon protonation, 2-, 3-, and 4-ethylphenols fragmented via the loss of ethylene, which facilitated their distinction from the isomeric 2,4-, 2,5-, and 3,4-dimethylphenols. Furthermore, the natural phenols formed stable adducts with C2H5+ and C3H5+ ions generated from methane upon CI. In contrast, additive phenols (with one or more tert-butyl groups) were predominantly ionized via electron abstraction to yield molecular radical cations and did not form adduct ions and generated some diagnostic fragment ions, such as ions of m/z 57 (tert-butyl cation). Most of the molecular radical cations of additive phenols also exhibited a methyl radical loss, while protonated additive phenols exhibited water loss. The limit of detection and the limit of quantitation were determined to be 1.3 μM (0.33 ppm) and 4.2 μM (1.08 ppm), respectively, and the linearity of quantitation was between 5 and 160 μM. Measurements of equimolar mixtures composed of additive and natural phenols demonstrated similar (within 10%) but not identical ionization efficiencies for these two compound types. Intra- and interday measurements of the signal intensities of the phenols were highly repeatable, with average relative standard deviations of 1.7 and 5.2%, respectively. The same method was employed to successfully characterize and quantify unknown phenols in alternative and petroleum-based jet fuel extracts. The petroleum-based Jet A fuel was found to contain a 1.5 times greater concentration of phenols than the alternative fuel. Jet A contained monomethylated phenols (108 Da), while the alternative fuel did not. Several phenols with molecular weights of 122, 136, and 150 Da were detected in both Jet A and the alternative fuel. The CI mass spectra suggested that some of these phenols had multiple methyl substituents. The information that can be acquired by using the GC/(CI) QqQ method will facilitate establishing links between the chemical compositions of fuels and fuel properties. Overall, the method was found to be robust and repeatable.

In Vivo ESR Spin Trapping Detection of Carbon-Centered α-Farnesene Radicals

Lyophilisates of the ascomycetes Penicillium solitum and Aspergillus niger converted alpha-farnesene to 7-hydroxyfarnesene as the major product. The radical mechanism of this bioconversion was proven by electron spin resonance (ESR) and GC-MS using the spin trapping technique. Intermediate carbon-centered radicals of alpha-farnesene were captured using two spin traps, 2-methyl-2-nitrosopropane and alpha-(4-pyridyl-1-oxide)- N- tert-butylnitrone, respectively. The evaluation of the coupling constants and hyperfine couplings of the ESR spectra showed that tertiary carbon radicals were trapped. The radical position at C7 of alpha-farnesene was derived from EI and CI mass spectra of the corresponding MNP spin adduct. The present study demonstrates that the complementary application of ESR and MS spectrometric data allows the detailed evaluation of a radical mechanism of a fungal terpene transformation reaction.

GC-MS detection and characterization of two laudanosine metabolites in urine as probable markers of atracurium administration

mentations, while the CI mass spectra exhibited both the protonated molecular ions and intense fragment ions (corresponding to base-peak ions in EI spectra) after TMS derivatization. However, the mass spectral libraries of both the National Institute of Standards and Technology (NIST) and Wiley characterized underivatized compound X1 as 1,2,3,4-tetrahydroisoquinoline6,7-dimethoxy-1-phenmethanol-2-methyl (TDPM) with match qualities of 96%. Nonetheless, this compound was excluded as a possible assignment of compound X1 based on the difference in molecular weights [313 for TDPM and 343 for X1 (Table 1)]. As can be deduced from the library match for compound X1 (i.e., TDPM) and as has been previously found for methyl-derivatized reticuline [1], the basepeak ions in EI-MS and intense fragment-peak ions in CI-MS, both of m/z 206 (Table 1), must have come from the dimethoxy-N-methyl-tetrahydroisoquinoline moiety (Fig. 1). The substantial similarities of the GC-MS data of compounds X1 and X2 to those of reticuline [1] offered the lead for their chemical structure elucidation. In reticuline (Fig. 1) characterization [1], the masses of 151 and 264 have been attributed to dimethoxybenzyl and methoxy-trimethylsilyloxy-N-methyl-tetrahydroisoquinoline moieties, respectively. Because the same values were observed for compound X2 and their sum accounts for the observed and calculated molecular weight of 415 (Table 1, Fig. 1), compound X2 can be assigned the chemical structure shown in Fig. 1 and given the chemical name 6-(or 7-)desmethyllaudanosine. Similarly, the masses of 137 and 209 observed for compound X1 (Table 1) could be associated with hydroxy-methoxybenzyl and methoxy-trimethylsilyloxy-benzyl moieties, respectively (Fig. 1). These masses (i.e., 137 and 209) together with the m/z 206 (which corresponds to Received: 20 June 2007 / Accepted: 16 August 2007 / Published online: 1 November 2007 © Japanese Association of Forensic Toxicology and Springer 2007

Dissociation Mechanism of HNIW Ions Investigated by Chemical Ionization and Electron Impact Mass Spectroscopy

AbstractChemical Ionization (CI) with Collision‐Induced Dissociation (CID) spectroscopy and Electron Impacting (EI) with metastable Mass analyzed Ion Kinetic Energy (MIKE) spectroscopy have been applied to study ionic dissociations of Hexanitrohexaazaisowurtzitane (HNIW). Similarities and differences between EI/MIKE and CI/CID mass spectra of HNIW were analyzed. In EI mass spectra, the ions [HNIW−n NO2]+ (n=2–5), such as the ion at m/z 347, were less frequent (1–2% relative abundance), but in CI mass spectra, these ions were very abundant. For some ions of large molar mass from HNIW, their dissociations pathways from parent ions to daughter ions were built according to CID and MIKE spectra. Molecular ions of HNIW with a protonated nitro group at five‐member ring seem more stable than at six‐member ring. The HNIW ions losing five of six nitro groups are very stable based on CID spectra, which agrees with some research results for thermal decomposition of HNIW in literature.

Identification and Quantification of Aerosol Polar Oxygenated Compounds Bearing Carboxylic or Hydroxyl Groups. 1. Method Development

In this study, a new analytical technique was developed for the identification and quantification of multifunctional compounds containing simultaneously at least one hydroxyl or one carboxylic group, or both. This technique is based on derivatizing first the carboxylic group(s) of the multifunctional compound using an alcohol (e.g., methanol, 1-butanol) in the presence of a relatively strong Lewis acid (BF3) as a catalyst. This esterification reaction quickly and quantitatively converts carboxylic acids to their ester forms. The second step is based on silylation of the ester compounds using bis(trimethylsilyl) trifluoroacetamide (BSTFA) as the derivatizing agent. For compounds bearing ketone groups in addition to carboxylic and hydroxyl groups, a third step was used based on PFBHA derivatization of the carbonyls. Different parameters including temperature, reaction time, and effect due to artifacts were optimized. A GC/MS in EI and in methane-CI mode was used for the analysis of these compounds. The new approach was tested on a number of multifunctional compounds. The interpretation of their EI (70 eV) and CI mass spectra shows that critical information is gained leading to unambiguous identification of unknown compounds. For example, when derivatized only with BF(3)-methanol, their mass spectra comprise primary ions at m/z M.+ + 1, M.+ + 29, and M.+ - 31 for compounds bearing only carboxylic groups and M.+ + 1, M.+ + 29, M.+ - 31, and M+. - 17 for those bearing hydroxyl and carboxylic groups. However, when a second derivatization (BSTFA) was used, compounds bearing hydroxyl and carboxylic groups simultaneously show, in addition to the ions observed before, ions at m/z M.+ + 73, M.+ - 15, M.+ - 59, M.+ - 75, M.+ - 89, and 73. To the best of our knowledge, this technique describes systematically for the first time a method for identifying multifunctional oxygenated compounds containing simultaneously one or more hydroxyl and carboxylic acid groups.

Ion trap mass spectrometry affords advances in the analytical and atmospheric chemistry of 2-hydroxy-2-methylpropanal, a proposed photooxidation product of 2-methyl-3-buten-2-ol

In the western United States, in areas where emissions of the biogenic hydrocarbon, 2-methyl-3-buten-2-ol (MBO) are high, MBO contributes significantly to the oxidative capacity of the atmosphere. Hydroxyl radical oxidation of MBO can play an important role in forming tropospheric ozone, and MBO reaction products may contribute to the formation of secondary organic aerosols [1–3]. Although 2-hdyroxy-2-methylpropanal was tentatively identified as a product from the reaction of MBO with ·OH in indoor chamber studies, the identity of the compound was not confirmed due to the lack of an authentic standard. Further, no data exists on the atmospheric generation and fate of 2-hydroxy-2-methylpropanal in the ambient environment. Herein, we provide further evidence that 2-hydroxy-2-methylpropanal is generated by ·OH reaction with MBO by identifying 2-hydroxy-2-methylpropanal in an indoor chamber experiment and in ambient air sampled in the Blodgett Forest, where MBO emissions are high. We analyzed 2-hydroxy-2-methylpropanal by using a method that relies on O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and bis-(trimethylsilyl) trifluoroacetamide (BSTFA) derivatization along with ion-trap mass spectrometry. Tentative identification of 2-hydroxy-2-methylpropanal was possible by using knowledge gained in this study regarding the mass spectrometry of PFBHA-BSTFA derivatives of carbonyls with primary, secondary, and tertiary −OH groups, and ado- and keto-acids. The identification was confirmed by comparing the methane CI mass spectra and relative gas chromatographic retention time obtained by analyzing 2-hydroxy-2-methylpropanal in a sample extract and a synthesized authentic standard. Since the standard became available at the end of this study (after all samples were analyzed), we also developed a method for semi-quantification of 2-hydroxy-2-methylpropanal, with a detection limit of 27 pptv in air. We used the method to provide the first ambient air measurements of 2-hydroxy-2-methylpropanal. The analyte is not commercially available, and hence other researchers who have not synthesized an authentic standard can employ the method.

Separation, identification, and quantification of amino acids in L-lysine fermentation potato juices by gas chromatography-mass spectrometry.

The amino acid composition of L-lysine fermentation juices from potatoes and cane molasses from a green biorefinery has been determined by gas chromatography-mass spectrometry. N-Methyl-N-tert(butyldimethylsilyl)tri-fluoroacetamide (MTBSTFA) was used as derivatization reagent to prepare the t-butyldimethylsilyl derivatives of the amino acids present in the juices. The amino acids in these derivatives were identified from both their EI and CI mass spectra and their retention times in the gas chromatogram, and they were quantified employing the GC response signals relative to cycloleucine as internal standard.

Gas Chromatography/Mass Spectrometry of Polyethylene Glycol Oligomers

Polyethylene glycol (PEG) oligomers, H(OC2H4O) nH, were analyzed by gas chromatography/mass spectrometry (GC/MS) for oligomers, n = 2–11, without indications of pyrolysis of the higher oligomers at oven temperatures of 330°C. The electron ionization (EI) mass spectra (70 eV and 12–14 eV) of these PEG oligomers contain only low molecular weight fragment ions and, essentially, no M+ ions. The low-voltage EI spectra contain more abundant high mass ions and allow easier identification of the PEG oligomers. The major fragment ions in all EI spectra are (C2H4O) xH+ at m/z 45, 89, 133 and 177. The base peak in the low-voltage spectra varies with molecular weight and suggests preferential cleavage at the second and third ether linkages. The relative molar sensitivities (70 eV EI) of PEG oligomers ( n = 1–6) are linear functions of molecular weight or polarizability ratios. The CH4 chemical ionization mass spectra of the PEG oligomers contain, predominantly, (C2H4O) xH+ ions at m/z 45, 89, 133 and 177. The relative abundances of MH+ ions vary markedly across the chromatographic peaks because these ions are formed predominantly by sample ion / sample molecule reactions. Proton transfer reactions from CH5+ and C2H5+ to the PEG oligomers are almost entirely dissociative. The i-C4H10 CI mass spectra of PEG oligomers contain MH+ as the base peaks. The relative abundances of MH+ ions do not vary significantly across the chromatographic peaks but do increase with increasing pressure of i-C4H10. The extent of decomposition of MH+ ions in i-C4H10 CI mass spectra increases with increasing molecular weight of the PEG oligomers. Relative molar sensitivities (CH4 CI and i-C4H10 CI) of PEG oligomers ( n = 1–6) are essentially the same linear functions of molecular weight ratio.

α-Phosphoryl sulfoxides. Part XII. The question of sulfinyl oxygen participation in the alkaline hydrolysis of α-phosphoryl sulfoxides

The course of the alkaline hydrolysis of (diphenoxyphosphoryl)methyl p-tolyl sulfoxide (8) has been elucidated by a combination of 18O isotopic labelling and mass spectrometric analysis of the hydrolysis products. The hydrolysis of the sulfoxide 8 containing 18O in the sulfinyl group afforded the corresponding phosphonic acid 9, which, upon methylation with diazomethane, was converted into [methoxy(phenoxy)phosphoryl]methyl p-tolyl sulfoxide (10) also containing 18O in the sulfinyl group, as demonstrated by the EI- and CI-mass spectra. The hydrolysis of 8 in 18O-enriched water followed by methylation with diazomethane gave the sulfoxide 10 in which 18O was incorporated into the phosphonic ester moiety. These results do not support a two-step mechanism for the hydrolysis of α-phosphoryl sulfoxides involving participation of the neighbouring sulfinyl group and formation of a cyclic oxathiaphosphetane intermediate. The latter is most probably formed in the mass spectrometric fragmentation process of α-phosphoryl sulfoxides.

Analysis of alkenes by copper ion chemical ionization gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry

A novel chemical ionization/fast atom bombardment (CI/FAB) source was used to analyse alkenes by chemical ionization mass spectrometry (CI-MS) using copper ions as the ionizing agent. The Cu(+)-CI mass spectra showed abundant pseudomolecular adduct ions [alkene-Cu](+) and characteristic fragment ions. Mass-analysed ion kinetic energy spectroscopy was used to study the product ions resulting from the decomposition of adduct ions and to eliminate background interferences derived from the copper ions. The major fragmentations permitted the localization of double bonds and minor fragments allowed the differentiation of alkene isomers. The CI/FAB source was coupled to a gas chromatograph and simple and complex mixtures of octene isomers were analysed by gas chromatography (GC)/Cu(+)-CI-MS and GC/Cu(+)-CI-MS/MS. Copyright 1999 John Wiley & Sons, Ltd.

The investigation of N‒dinitrophenyl derivatives of amino acids by electron/chemical ionization using a particle beam interface1

The EI and CI mass spectra of DNP‒amino acids and oligopeptides give characteristic mass spectra when a particle beam interface is used for introduction. They differ from mass spectra obtained after direct insertion into the ion source: In the particle beam interface the major part of the molecules suffers degradation by contact with metal surfaces such as decarboxylation and reduction of the nitro groups. The final products are benzimidazole derivatives carrying in 2‒position the residue of the respective amino acid. These products show characteristic fragmentation reactions which allow to identify isomeric amino acids. For DNP‒di‒ and oligopeptides an identification of the N‒terminal amino acid is always possible, that of the C‒terminus with restrictions.

Determination of linear alkylbenzenesulfonates and their degradation products in water samples by gas chromatography with ion-trap mass spectrometry

A method was developed for the analysis of linear alkylbenzenesulfonates (LAS) and their degradation products, sulfophenylcarboxylic acids (SPC), in samples of sewage effluent and river water. This method involved extraction of the samples by graphitized carbon black cartridge, esterification by a two-step thionyl chloride–trifluoroethanol derivatization procedure, and separation, identification and quantitation by ion-trap GC–MS with EI and low pressure CI modes. High selectivity with few signals was observed in the low pressure CI mass spectra of LAS and SPC. Enhanced sensitivity with protonated molecular ion chromatograms of homologous C 10–C 13 LAS by CI-MS permit the determination of LAS and SPC at trace concentrations in environmental samples. Recovery rates of LAS and SPC in spiked water samples ranged from 75 to 112% with R.S.D. values from 3 to 26%. The limit of quantitation for both LAS and SPC was estimated to be 0.01 μg/l in 100 ml of water sample.

Gas chromatography—chemical ionization mass spectrometry in amino acid analysis of pyoverdins

The application and advantages of positive chemical ionization with methane [CI(CH 4)] for gas chromatography-mass spectrometry (GC-MS) of perfluoroacyl amino acid alkyl esters are discussed. All investigated amino acids show [M + H] +, [M + C 2H 5] +, and [(M + H) − C 3H 6] +. By a comparison of the electron ionization (EI) and CI(CH 4) mass spectra the analysis of amino acid mixtures by GC-MS will give reliable results also in the case of isomeric compounds or of (partial) decomposition during analysis.

Gas-phase reactions of glycine, alanine, valine and their N-methyl derivatives with the nitrosonium ion, NO+.

The gas-phase reactions of the nitrosonium ion, NO+ with the amino acids glycine, alanine and valine and their N-methyl derivatives were investigated under chemical ionization mass spectrometric (CIMS) conditions. Two products were observed in all cases: the formation of the iminium ion and the formation of an [M-H]+ ion. The latter product is consistent with a reaction channel involving hydride abstraction by NO+, and was confirmed by (i) examining the Ar+CI mass spectra of the same amino acids under similar source conditions and (ii) examining the unimolecular fragmentation reactions of the [M + H]+ ions of the N-nitroso-N-methyl derivatives of each of the amino acids in a tandem mass spectrometer. Further insights into the reaction of glycine with NO+ were obtained by performing ab initio calculations (at the MP2/6-31G* parallel HF/6-31G* level). These results indicate that four reactions are thermodynamically viable for glycine: (i) hydride abstraction; (ii) iminium ion formation (with concomitant loss of HONO and CO); (iii) diazonium ion formation; and (iv) diazonium ion formation followed by loss of N2. Possible reasons why reactions (iii) and (iv) are not observed are discussed, and comparisons with solution reactivity and the gas-phase reactivity of NO+ are also made.

N-chloroaldimines. 4. Identification in a chlorinated municipal wastewater by gas chromatography/mass spectrometry

N-Chloroaldimines are formed in aqueous solution by chlorination of nonpolar α-amino acids with ≥2 equiv of aqueous chlorine at pH 7. Four N-chloroaldimines were identified in chlorinated municipal wastewater with varying degrees of confidence. The compounds were isolated from wastewater by ether extraction and concentrated by Kuderna-Danish evaporation before GC/MS analysis. The presence of N-chloroisobutyraldimine (I), a product of the chlorination of valine, was confirmed in two municipal wastewaters (primary effluents) by comparison of its retention time and EI and CI mass spectra with those of standards.

Stereochemical Effects in Chemical Ionization Mass Spectrometry Using Chiral Reagent Gases.

The gas chromatographic resolution of isoborneol and borneol enantiomers were achieved by capillary column coated with chiral stationary phase. The gas chromatography/chemical ionization mass spectrometry (GC/CIMS) were performed using (S)-(+)-1-amino-2-propanol, (R)-(−)-1-amino-2-propanol, (S)-(+)-2-amino-1-propanol, and (R)-(−)-2-amino-1-propanol as chiral reagent gases. The CI mass spectra could be obtained with good reproducibilities. It was found that the CI mass spectra of the enantiomers could be distinguished when a chiral reactant ion attached to a chiral functional group of the sample molecule.

Production of phomozin in sunflower following artificial inoculation with Phomopsis helianthi

Sunflower plants artificially infected by Phomopsis helianthi contain the phytotoxin phomozin which has been identified both by its HPLC-chromatographic behaviour, UV spectrum, EI and CI mass spectra, and biological activity. Phomozin is produced in vivo both in susceptible and, to a lesser extent, in tolerant cultivars of sunflower.

Porphyrin pyrrole sequencing: low-energy collision-induced dissociation of (M + 7H)+ generated in-situ during ammonia chemical ionization

A method for pyrrole sequencing of porphyrins, based on high-pressure ammonia chemical ionization mass spectrometry/mass spectrometry (CI-MS/MS), is presented. High-pressure ammonia CI of porphyrins promotes formation of reduced molecular species and tri-, di-, and monopyrrolic fragment ions. The masses and pattern of the pyrrolic fragment ions can be used to determine the pyrrole sequence of the porphyrin. However, because of the complex ion source chemistry involved, these CI mass spectra are difficult to reproduce and are complicated by a plethora of structurally uninformative peaks. As such, pyrrole sequence elucidation based on the CI mass spectrum alone can be arduous, especially in the case of asymmetrically substituted porphyrins. In this paper, the MS/MS daughter ion spectrum of in situ formed (M + 7H){sup +} (i.e., the protonated porphyrinogen) is used to determine the porphyrin pyrrole sequence. Low-energy (30-100 eV) collision-induced dissociation (CID) of (M + 7H){sup +}, using a hybrid mass spectrometer of BEqQ geometry, yields, specific patterns of tri-, di-, and monopyrrolic daughter ions from which the pyrrole sequence of the porphyrin and combined mass of the substituents on the individual pyrroles can be determined. Several porphyrins of different pyrrole sequence are used to demonstrate the CI-MS/MS sequencing method. Themore » capability of the CI-MS/MS method to sequence the pyrroles of porphyrins within a simple mixture of nonisobaric porphyrins is also demonstrated.« less

A new matrix system in fast atom bombardment mass spectrometry of prenylated- and geranylated-phenolic compounds.

A 1 : 1 (v/v) mixture of m-nitrobenzyl alcohol (m-NBA) and 2,2'-dithiodiethanol (DTDE, HOCH2CH2SSCH2CH2OH) was applied as a new matrix system to FAB mass spectra of prenylated- and geranylated-phenolic compounds, with which the matrix was relatively involatile and durable for a long period of time. This resulted in the good reproducibility of the FAB spectra. The FAB spectra were compared with the corresponding EI and CI mass spectra. The FAB spectra gave the intense molecular ions M+· and the fragment ions.