Negative-ion Chemical Ionization Mass Spectra Research Articles

Quantification of Carbonate by Gas Chromatography−Mass Spectrometry

Carbon dioxide and carbonates are widely distributed in nature, are constituents of inorganic and organic matter, and are essential in vegetable and animal organisms. CO(2) is the principal greenhouse gas in the atmosphere. In human blood, CO(2)/HCO(3)(-) is an important buffering system. Quantification of bicarbonate and carbonate in inorganic and organic matter and in biological fluids such as blood or blood plasma by means of the GC-MS technology has been impossible so far, presumably because of the lack of suitable derivatization reactions to produce volatile and thermally stable derivatives. Here, a novel derivatization reaction is described for carbonate that allows for its quantification in aqueous alkaline solutions and alkalinized plasma and urine. Carbonate in acetonic solutions of these matrices (1:4 v/v) and added (13)C-labeled carbonate for use as the internal standard were heated in the presence of the derivatization agent pentafluorobenzyl (PFB) bromide for 60 min and 50 °C. Investigations with (12)CO(3)(2-), (13)CO(3)(2-), (CH(3))(2)CO, and (CD(3))(2)CO in alkaline solutions and GC-MS and GC-MS/MS analyses under negative-ion chemical ionization (NICI) or electron ionization (EI) conditions of toluene extracts of the reactants revealed formation of two minor [i.e., PFB-OCOOH and O=CO(2)-(PFB)(2)] and two major [i.e., CH(3)COCH(2)-C(OH)(OPFB)(2) and CH(3)COCH=C(OPFB)(2)] carbonate derivatives. The latter have different retention times (7.9 and 7.5 min, respectively) but virtually identical EI and NICI mass spectra. It is assumed that CH(3)COCH(2)-C(OH)(OPFB)(2) is formed from the reaction of the carbonate dianion with two molecules of PFB bromide to form the diPFB ester of carbonic acid, which further reacts with one molecule of acetone. Subsequent loss of water finally generates the major derivative CH(3)COCH=C(OPFB)(2). This derivatization reaction was utilized to quantify total CO(2)/HCO(3)(-)/CO(3)(2-) (tCO(2)) in human plasma and urine by GC-MS in the NICI mode by selected ion monitoring of the anions [M-H](-) of CH(3)COCH=C(OPFB)(2) at m/z 461 for the endogenous species and m/z 462 for the internal standard (13)CO(3)(2-). Oral intake of the carboanhydrase inhibitor drug acetazolamide by two healthy volunteers resulted in temporary increased excretion of tCO(2) in the urine. The method is specific for carbonate, accurate, sensitive and should be applicable to various matrices including human fluids and environmental samples.

Evidence for in situ ethanolamine phospholipid adducts with hydroxy-alkenals

Hydroxy-alkenals, such as 4-hydroxy-2(E)-nonenal (4-HNE; from n-6 fatty acids), are degradation products of fatty acid hydroperoxides, including those generated by free radical attack of membrane polyunsaturated fatty acyl moieties. The cytotoxic effects of hydroxy-alkenals are well known and are mainly attributable to their interaction with different molecules to form covalent adducts. Indeed, ethanolamine phospholipids (PEs) can be covalently modified in a cellular system by hydroxy-alkenals, such as 4-HNE, 4-hydroxy-2(E)-hexenal (4-HHE; from n-3 fatty acids), and 4-hydroxy-dodecadienal (4-HDDE; from the 12-lipoxygenase product of arachidonic acid), to form mainly Michael adducts. In this study, we describe the formation of PE Michael adducts in human blood platelets in response to oxidative stress and in retinas of streptozotocin-induced diabetic rats. We have successfully characterized and evaluated, for the first time, PEs coupled with 4-HHE, 4-HNE, and 4-HDDE by gas chromatography-mass spectrometry measurement of their ethanolamine moieties. We also report that aggregation of isolated human blood platelets enriched with PE-4-hydroxy-alkenal Michael adducts was altered. These data suggest that these adducts could be used as specific markers of membrane disorders occurring in pathophysiological states with associated oxidative stress and might affect cell function.

Novel approach to separation and identification of organometallic compounds in complex mixtures by means of particle beam liquid chromatography/mass spectrometry: the case of diphosphine-substituted selenido iron and ruthenium clusters

The particle beam liquid chromatography/mass spectrometry (PB LC/MS) characterization of diphosphine-substituted selenido iron and ruthenium clusters is reported. The clusters considered result from the reaction between the diphosphine diselenides (Ph2PSe)2R [R = CH2, dppmSe2; R = CH2CH2, dppeSe2; R = (C5H4)2Fe, dppfcSe2] and Fe3(CO)12 and Ru3(CO)12. Complex reaction mixtures were separated under adsorption chromatographic conditions and characterized on-line by means of the positive-ion and negative-ion chemical ionization mass spectra of the eluates. The PB LC/MS analysis of the crude reaction mixtures proved useful, avoiding sample manipulation and/or sample degradation; this is particularly important for those compounds sensitive to oxygen or light, or which are unstable in solution. The spectra obtained showed characteristic fragmentation patterns and detailed structural information. © 1998 John Wiley & Sons, Ltd.

Normal-phase and reversed-phase high-performance liquid chromatographic behaviour and particle beam mass spectrometric characterization of alkyne-substituted iron–carbonyl clusters

The chromatographic behaviour of seven iron–carbonyl compounds substituted with alkynes R 2C 2 was studied both in normal-phase and reversed-phase chromatography. Several kinds of stationary phases were considered, including silica, CN, C 18 and phenyl columns. Positive-ion and negative-ion chemical ionization mass spectra of the compounds obtained with a particle beam MS system in flow injection analysis are reported. LC–MS experiments were performed for confirmation purposes and in order to check the integrity of the analytes after the LC separation.

Use of Particle Beam Liquid Chromatography/Mass Spectrometry for the Characterization of Chromium Aminocarbene Complexes

Chromium carbenes are used in organic synthesis as reagents to obtain molecules of biological interest. In this work a particle beam (PB) coupled liquid chromatography/mass spectrometry (LC/MS) system was used for the characterization of a mixture of chromium aminocarbene complexes. Three of them are new compounds. The separation of the examined complexes was performed using normal-phase chromatography. The acquisition of electron ionization, positive-ion and negative-ion chemical ionization mass spectra of the eluates was accomplished. The capability of PB LC/MS technique in the on-line characterization of organometallic compounds is highlighted. In addition, the fragmentation patterns of all the compounds considered are discussed. © 1997 John Wiley & Sons, Ltd.

Negative-ion Chemical Ionization of Amphetamine Derivatives

The negative-ion chemical ionization (NICI) mass spectra of the heptafluorobutyryl (HFB) and pentafluorobenzoyl (PFBz) derivatives of several amphetamines and N-substituted amphetamines were obtained. The HFB derivatives of amphetamine and its ring-substituted congeners were each found to undergo predominant loss of one molecule of hydrogen fluoride, while the corresponding PFBz derivatives each underwent sequential loss of two molecules of hydrogen fluoride followed by the loss of either a methyl or an aryl group. The HFB derivatives of the N-substituted amphetamines were found to undergo sequential loss of four molecules of hydrogen fluoride while the corresponding PFBz derivatives produced high-abundance molecular ions. NICI mass spectra of deuterium-labelled amphetamine derivatives were obtained and the order of hydrogen elimination was studied. These findings explain previous observations of hydrogen fluoride loss by the amphetamine derivatives and define potential applications of NICI mass spectrometry to the analysis of these compounds.

Negativeion Chemical Ionization of Amphetamine Derivatives

The negative-ion chemical ionization (NICI) mass spectra of the heptafluorobutyryl (HFB) and pentafluorobenzoyl (PFBz) derivatives of several amphetamines and N-substituted amphetamines were obtained. The HFB derivatives of amphetamine and its ring-substituted congeners were each found to undergo predominant loss of one molecule of hydrogen fluoride, while the corresponding PFBz derivatives each underwent sequential loss of two molecules of hydrogen fluoride followed by the loss of either a methyl or an aryl group. The HFB derivatives of the N-substituted amphetamines were found to undergo sequential loss of four molecules of hydrogen fluoride while the corresponding PFBz derivatives produced high-abundance molecular ions. NICI mass spectra of deuterium-labelled amphetamine derivatives were obtained and the order of hydrogen elimination was studied. These findings explain previous observations of hydrogen fluoride loss by the amphetamine derivatives and define potential applications of NICI mass spectrometry to the analysis of these compounds.

Characterization of chromium-carbene complexes by high-performance liquid chromatography-mass spectrometry with particle beam interface

High-performance liquid chromatography (HPLC) coupled with mass spectrometric (MS) detection was used to separate and characterize a series of chromium -aminocarbene and alkoxycarbene complexes of the Fischer type, some of which were synthesized as new compounds. Chromium-carbene complexes are known to have interesting photochemical properties. The separation of all the compounds examined was performed under normal-phase conditions and a particle beam LC-MS interface was used. The acquisition of positive-ion and negative-ion chemical ionization mass spectra of the eluates was performed. The use of the LC-PB-MS system demonstrated the potential role of this technique in the elucidation of the structure of polar organometallic compounds, such as the carbene complexes of chromium examined.

Comparison of high resolution gas chromatography with electron impact and negative ion mass spectrometry detection for the determination of coplanar polychlorobiphenyl congeners in sewage sludges.

The three most toxic coplanar PCB 77, 126 and 169 have been identified and quantified at ultra trace levels (0.02-4.8 ng/gdw) in swiss sewage sludge samples applying high resolution capillary gas chromatography (HRGC) and electron impact (EI) as well as negative ion chemical ionization (NCI) mass spectrometry (MS). NCI mass spectra have been dominated by the molecular ion as base peak and virtually no fragmentation has been observed. Detection limits of the planar PCB under single ion monitoring (SIM) conditions have been typically 100 fg for NCI-MS and 1 pg for EI-MS. NCI-MS was the preferred detection method for the determination of very low concentrations of these important contaminants in sewage sludge samples.

Negative ions generated by reactions with oxygen in the chemical ionization source. II. The use of wall‐catalyzed oxidation reactions for differentiation of polycyclic aromatic hydrocarbons and their methyl derivatives

AbstractPolycyclic aromatic hydrocarbons (PAH) undergo wall‐catalyzed oxidation reactions, in conjunction with electron‐and ion‐molecule reactions, when oxygen is present in the chemical ionization source. Under conditions that promote these wall‐catalyzed oxidation reactions (addition of oxygen, elevated ion source temperature) oxidized products are easily detected by measurement of the negative ion chemical ionization (NICI) mass spectra. The NICI mass spectra are dominated by ions that result from electron‐capture ionization of oxidation products such as ketones, quinones and anhydrides. In this study the NICI mass spectra of 30 PAH and 46 methyl‐substituted PAH were measured. These spectra can be used to differentiate certain isomeric PAH based upon differences in molecular structure. Of particular interest are ions that appear in the spectra of methyl‐substituted PAH, which can provide information regarding the position of methyl substituents.

Formation of an unusual MH− ion in the methane negative-ion chemical ionization mass spectra of chlorprothixene and aromatic sulfur compounds

The methane negative-ion chemical ionization (NCI) mass spectrum of chlorprothixene shows an unusual MH− ion. This ion can be accounted for by electron capture followed by H˙ transfer from the reagent gas. The most probable site of electron attachment was concluded to be related to the sulfur atom of the thioxanthene ring based on the observation of analogous ions for structurally related compounds, all containing a heterocyclic sulfur. The MH− ion observed with methane as the reagent gas was shifted to MD− when tetradeuteromethane was used in place of methane. The ratio of [M H]− to MH− did not change with emission current suggesting that the process is independent of the radical concentration in the CI plasma. Consistent with this observation is the lack of CH3˙ or C2H5˙ adduct ions in the NCI mass spectrum and the fact that gold-plating the ion source did not decrease the proportion of MH−. Also, this mechanism is consistent with thermochemical considerations of reactions of a phenyl radical with various alkanes and observations of ions formed by methane NCI from model compounds. Therefore, unlike other MH− ions observed in methane NCI mass spectra, the mechanism of formation does not appear to involve a hydrogen radical addition followed by electron capture.

Negative ion chemical ionization mass spectrometry—binding of molecules to bromide and iodide anions

AbstractThe analytical potential of negative ion chemical ionization (NICI) mass spectrometry utilizing dibromodifluoro‐methane (CF2Br2) and iodomethane (CH3I)/methane (CH4) as reagent gases is examined. The NICI mass spectrum of CF2Br2 contains Br−, [HBr2]− and [CF2Br3]− anions. Weak acids (i.e. those acids with approximately ΔH°(acid) values between 1674 and 1464 kJ mol−1) react with Br− to produce minor yields of the hydrogen−bonded bromide attachment [MH + Br]− anion or are unreactive. Strong acids (i.e. those acids with approximately ΔH°(acid) > 1464 kJ mol−1) produce primarily [MH + Br]− anions with a minor yield of proton transfer [M  H]− anion. The NICI spectrum of CH3I/CH4 is dominated by I−. Weak acids react with I− to yield minor amounts of [MH + 1]− or are unreactive. Strong acids produce only [MH + l]− anions. From a consideration of the gas‐phase basicity of the halide anion and the binding energy of the hydrogen‐bonded halide attachment adduct, thermochemical data are used as a potential guide to rationalize or predict the ions observed in NICI mass spectra.

Differentiation of methyl substituted fluorenes, anthracenes and benz[a]anthracenes using surface‐catalyzed oxidation reactions and negative ion chemical ionization mass spectrometry

AbstractMethyl‐substituted polycyclic aromatic hydrocarbons (PAH) are shown to undergo surface‐catalyzed reactions with oxygen. These reactions generate oxidized products, which include aldehydes, quinones, and anhydrides. The products dominate the O2/N2 negative ion chemical ionization (NICI) mass spectra of methyl‐PAH when the ion source temperature is elevated to 300°C. The NICI mass spectra of methyl‐PAH measured under these conditions show ions that can be used to distinguish the position of methyl groups substituted on fluorene, anthracene, and benz[a]anthracene isomers.

Positive and negative ion chemical ionization mass spectra of amino acid carboxy-n-butyl EsterN-Pentafluoropropionate Derivatives

The positive and negative chemical ionization mass spectra of 29 amino acid carboxy-n-butyl ester N-(O,S)-Pentafluoropropionate derivatives hae been determined. The positive ion (PI) mass spectra conform to the expected fragmentation patterns for this amino acid derivative but their methane negative ion chemical ionization (NICI) mass spectra displayed marked differences between various amino acid classes and bvetween positional isomers within the same class. Isomeric butyric acid (α, β and γ) and tyrosine (o, m amd p-hydroxylation) derivatives all had remarkably difterent NICI mass spectra. Aliphatic amino acid CO2-n-butyl-N-PFP derivatives (except glycine) can be readily recognized by a characteristic fragmentation process corresponding to [M–H–C4CO2H]−. Deuterium labellung studies were used to delineate some of the major NICI fragmentation processes. While the PICI mass spectra all gave comparable detection responses differences were observed with various amino acids when operating in the NICI mode. The order of sensitivity of detection for six representative amino acid-carboxy-n-butyl-N-PFP derivatives were: hydroxyproline > lysine > cysteine > glycine=leucine=methionine in the ratio of 100:20:7:1. In PICI mass spectrometry derivatized leucine yielded a response 25 times less than its NICI mass spectrometric value.

Preparation of pentafluorobenzyl esters of arachidonic acid lipoxygenase metabolites : Analysis by gas chromatography and negative-ion chemical ionization mass spectrometry

5-Hydroxyeicosatetraenoic acid (5-HETE) and leukotriene B 4 have recently been shown to possess potent chemotactic and chemokinetic properties. Because of the very low concentrations found in certain biological systems, negative-ion chemical ionization mass spectrometry has been investigated as a potential assay method for detecting these compounds. A facile derivatization to form the pentafluorobenzyl esters, and clean up are reported for these compounds at the 15-ng level. Gas chromatographic properties, negative-ion chemical ionization mass spectra, and positive-ion electron impact spectra are reported for the pentafluorobenzyl ester, trimethylsilyl ether derivatives of 5-HETE and leukotriene B 4 isomers.

Determination of isomeric polycyclic aromatic hydrocarbons in air particulate matter by high-resolution gas chromatography/negative ion chemical ionization mass spectrometry

High-resolution gas chromatography combined with electron capture negative ion chemical ionization (NICI) mass spectrometry looks to be a promising method for the detection of mutagenic and/or carcinogenic polycyclic aromatic hydrocarbons (PAH). When methane/nitrous oxide mixtures are used as reagent gas, (M - H)/sup -/, M/sup -/, (M + OH)/sup -/, (M - H + NO)/sup -/, and (M - H + N/sub 2/O)/sup -/ are formed in the ion source. Many isomeric PAH can be identified by significant differences in the abundance of these ions. NICI mass spectra and response factors obtained by both techniques are reported for 22 reference PAH. Some practical and instrumental aspects of the NICI mode are discussed. The method has been used for differentiation of isomeric benzofluoranthenes and benzofluorenes from methylfluoranthenes as well as for the determination of PAH in air particulate extracts. 2 figures, 3 tables.

Formation and reactions of negative ions relevant to chemical ionization mass spectrometry. I. CL mass spectra of organic compounds produced by F- reactions.

A systematic study of the negative-ion chemical ionization mass spectra produced by the reaction of F(-) with a wide variety of organic compounds has been accomplished. A time-of-flight mass spectrometer fitted with a modified high pressure ion source was employed for these experiments. The F(-) reagent ion was generated from CF(3)H or NF(3), typically at an ion source pressure of 100 mum. In pure NF(3), F(-) is the major ion formed and constitutes more than 90% of the total ion intensity. While F(-) is also the major primary ion formed in pure CF(3)H, it undergoes rapid ion-molecule reactions at elevated source pressures, yielding (HF)(n)F(-) (n = 1-3) ions, which makes CF(3)H less suitable as a chemical ionization reagent gas. Among the organic compounds investigated were carboxylic acids, ketones, aldehydes, esters, alcohols, phenols, halides, nitriles, nitrobenzene, ethers, amines and hydrocarbons. An intense (M - 1)(-) ion was observed in the F(-) chemical ionization mass spectra of carboxylic acids, ketones, aldehydes and phenols. Alcohols yield only (M + F)(-) ions upon reaction with F(-). A weaker (M + F)(-) ion was also detected in the F(-) chemical ionization spectra of carboxylic acids, aldehydes, ketones and nitriles. The F(-) chemical ionization mass spectra of esters, halides, nitriles, nitrobenzene and ethers are characterized primarily by the ions, RCOO(-), X(-), CN(-), NO(2) (-), and OR(-), respectively. In addition, esters show a very weak (M - 1)(-) ion (except formates). In the F(-) chemical ionization spectra of some aliphatic alkanes and o-xylene, a very weak (M + F)(-) ion was observed. Amines and aliphatic alkenes exhibit only insignificant fragment ions under similar conditions, while aromatic hydrocarbons, such as benzene and toluene are not reactive at all with the F(-) ion. The mechanisms of the various reactions mentioned are discussed, and several experimental complications are noted. In still other studies, the effects of varying several experimental parameters, including source pressure, relative proportions of the reagent and analyte, and other ion source parameters, on the observed chemical ionization mass spectra were also investigated. In a mixture of NF(3) and n-butanol, for example, the ratio of the intensities of the ions characteristic of the alcohol to that of the (HF)(n)F(-) ion was found to decrease with increasing sample pressure, with increasing NF(3) pressure, and with increasing electron energy. No significant effects on the spectra were observed to result from variation of the source repeller field or the source temperature. The addition of argon to the source as a potential moderator did not alter the F(-) chemical ionization spectrum significantly, but the use of oxygen appears to inhibit formation of the (HF)(n)F(-) cluster ion. The advantages of using F(-) as a chemical ionization reagent are discussed, and comparisons are made with other reagent ions.