Negative Chemical Ionization Mass Spectra Research Articles

Mass spectra of methyl esters of brominated fatty acids and their presence in soft drinks and cocktail syrups

Brominated vegetable oil (BVO) is frequently used as a solubility transmitter in soft drinks. Being banned in Europe and Japan but permitted in the United States and Canada, there is a need for analytical methods suitable for use in food control. Brominated fatty acids in BVO are usually determined by gas chromatography (GC) after their conversion into the corresponding methyl esters. GC with mass spectrometry (MS) was used to record the electron ionization (EI) and negative ion chemical ionization (NICI) mass spectra of relevant brominated fatty acid methyl esters synthesized for this purpose. Brominated fatty acids obtained from transesterified BVO from soft drink and syrup samples were also analyzed. GC/NICI-MS was the most sensitive method for the detection of brominated fatty acids but GC/EI-MS was found to be more suited for quantification due to the formation of more selective fragment ions in the higher mass range. Suitable ions were selected for determination of the methyl esters of brominated fatty acids in the selected ion monitoring (SIM) mode. Artifacts produced by the transesterification of BVO with boron trifluoride were observed and discussed. BVO was also quantified in three syrup samples commercially produced for use in cocktails/long drinks. In one of the syrup samples that tested positive, BVO was not labelled in the ingredient list. Bromination experiments produced evidence that one or more Br2 -18:0 isomers identified as a shoulder peak of threo-9,10-dibromooctadecanoic acid in several soft drink and syrup samples originated from the bromination of partly hydrogenated plant oil. BVO was determined for the first time in syrup samples. Attention should be paid to the problem of BVO occurring unlabeled in soft drinks and cocktail syrups imported from North America.

Identification and Structural Elucidation of Corrosion Inhibiting Long-Chain N-1-Alkyl-1,3-propanediamines by GC–MS

Gas chromatography–mass spectrometry has been used to identify long-chain (C8–C18) N-1-alkyl-1,3-propanediamines after derivatization with trifluoroacetic anhydride. Electron impact ionization and negative chemical ionization mass spectra of trifluoroacetylated derivatives of the identified N-1-alkyl-1,3-propanediamines are presented for the first time. The corrosion inhibiting long-chain N-1-alkyl-1,3-propanediamines were applied in the preparation and investigation of a new anticorrosive and antifouling formulation for water–steam circuit of energy systems in the power industry. Using the GC–MS data, it was possible to identify residues of the N-1-alkyl-1,3-propanediamines in complex samples of boiler water from the power plant after solid-phase extraction and acylation.

Mass spectral studies of perfluorooctane sulfonate derivatives separated by high‐resolution gas chromatography

The mass spectral characteristics of perfluorooctane sulfonate (PFOS, C(8)F(17)SO(3)-) isomers present in technical PFOS were obtained using high-resolution gas chromatography (HRGC) combined with mass spectrometry (MS). To make PFOS amenable to HRGC separation, a simple derivatization procedure was developed. The method involved the conversion of PFOS into the iso-propyl ester using iso-propanol as the derivatization reagent under acidic conditions. Mass spectra were generated employing electron ionization (EI) and negative chemical ionization (NCI). Interpretation of fragment ions was possible due to the use of deuterium-labeled iso-propanol as derivatization reagent, which induced mass shifts in the electron ionization (EI) and negative chemical ionization (NCI) mass spectra. HRMS allowed the accurate mass measurement of important EI fragments and confirmed the derivatization reaction as well as the proposed fragmentation pathway involving rearrangement. Moreover, the high resolution provided by HRGC enabled the separation of eleven PFOS isomers present in the technical product. This is an improvement over the previously reported high-performance liquid chromatography (HPLC) separation. A complete identification of all isomers was not possible due to lack of pure reference materials. Finally, the developed derivatization procedure was successfully applied to perfluoroalkyl carboxylates (PFCA) and corresponding fragmentation involving rearrangement of the derivatized PFCA was observed. The described qualitative derivatization offers a promising alternative technique for the separation and identification of isomers of perfluoroalkyl sulfonates and carboxylates by HRGC/MS.

Nitramine Anion Fragmentation: A Mass Spectrometric and Ab Initio Study

The fragment ion formation characteristics of the radical anions generated from hexahydro-1,3,5-trinitrotriazine (RDX) and its three nitroso metabolites were studied using GC/MS with negative chemical ionization (NCI) to understand the fragmentation mechanisms responsible for the formation of the most abundant ions observed in their NCI mass spectra. Ab initio and density functional theory calculations were used to calculate relative free energies for different fragment ion structures suggested by the m/z values of the most abundant ions observed in the NCI mass spectra. The NCI mass spectra of the four nitramines are dominated by ions formed by the cleavage of nitrogen-nitrogen and carbon-nitrogen bonds in the atrazine ring. The most abundant anions in the NCI mass spectra of these nitramines have the general formulas C(2)H(4)N(3)O (m/z 86) and C(2)H(4)N(3)O(2) (m/z 102). The analyses of isotope-labeled standards indicate that these two ions are formed by neutral losses that include two exocylic nitrogens and one atrazine ring nitrogen. Our calculations and observations of the nitramine mass spectra suggest that the m/z 86 and m/z 102 ions are formed from either the (M--NO)(-) or (M--NO(2))(-) fragment anions by a single fragmentation reaction producing neutral losses of CH(2)N(2)O or CH(2)N(2)O(2) rather than a set of sequential reactions involving neutral losses of HNO(2) or HNO and HCN.

Solid-phase extraction-gas chromatography and solid-phase extraction-gas chromatography–mass spectrometry determination of corrosion inhibiting long-chain primary alkyl amines in chemical treatment of boiler water in water-steam systems of power plants

Gas chromatography with simultaneous flame-ionization detection (FID) and a nitrogen-phosphorus detection (NPD) as well as gas chromatography–mass spectrometry (GC/MS) has been used to characterize long-chain primary alkyl amines after derivatization with trifluoroacetic anhydride (TFAA). Electron impact ionization- (EI) and negative chemical ionization (NCI) mass spectra of trifluoroacetylated derivatives of the identified tert-octadecylamines are presented for the first time. The corrosion inhibiting alkyl amines were applied in a water-steam circuit of energy systems in the power industry. Solid-phase extraction (SPE) with octadecyl bonded silica (C 18) sorbents followed by gas chromatography were used for quantification of the investigated tert-octadecylamines in boiler water, superheated steam and condensate samples from the power plant. The estimated values were: 89 μg l −1 ( n = 5, RSD = 7.8%), 45 μg l −1 ( n = 5, RSD = 5.4%) and 37 μg l −1 ( n = 5, RSD = 2.3%), respectively.

Spectroscopic studies on Isatin-3-Semicarbazone and Isatin-3-Thiosemicarbazone

The configurations of semi-and thiosemicarbazone derivatives of isatin are assigned by means of 1H and 13C NMR Spectroscopy including NOE difference spectra, IR and electronic spectral data of these compounds are also reported and discussed. The electron impact (EI), fast atom bombardment (FAB) and negative ion chemical ionization (NICI) mass spectra are also reported. Fragmentation of molecular and pseudomolecular ions are tabulated and rationalized. KEY WORDS: IH NMR, 13C NMR, Semicarbazone thiosemicarbazone, mass spectra, negative ion chemical ionization, fragmentation. Global Jnl Pure and Applied Sciences Vol.10(4) 2004: 545-553

A new peroxycarboxylic nitric anhydride identified in the atmosphere: CH2=CHC(O)OONO2 (APAN)

We detected a peroxyacyl nitrate (PAN)‐type compound, peroxyacryloyl nitrate (CH2=CHC(O)OONO2, APAN) which has not previously been reported in the atmosphere. Identification of APAN was made from negative ion chemical ionization (NICI) mass spectra of a cryogenically concentrated ambient air sample by comparison with a synthesized standard. The thermally fragile nature of the compound, and the retention time of the synthesized standard provide additional evidence for the existence of APAN in ambient air. Observations made at a suburban site in Tokyo, and at Rishiri Island, a remote site in northern Japan, suggest the ubiquitous presence of APAN in the global atmosphere. While its mixing ratio was usually low (<1% of PAN), high‐APAN episodes (∼4% of PAN) were observed at Rishiri Island. APAN can be formed from acrolein, which is directly emitted from vehicle exhaust, and may be produced by oxidation of 1,3‐butadiene and aromatics. Further measurements of APAN along with acrolein and other NMHCs are required to understand its distribution, behavior, and sources in the atmosphere.

Reactions of O −· with methyl benzoate: a negative ion chemical ionization and Fourier transform ion cyclotron resonance study

The reactions of O −· with methyl benzoate have been examined by the measurement of negative ion chemical ionization (NICI) mass spectra using a CI source, with confirmatory studies carried out on a Fourier transform ion cyclotron resonance mass spectrometer. Reaction mechanisms have been elucidated using isotopically labeled esters. Nucleophilic attack at the carbonyl carbon and the aromatic ring were important reaction pathways. Nucleophilic attack at the carbonyl carbon was followed by the production of products (C 6H 5CO 2 − and CH 3OCO 2 −) characteristic of radical, β-fragmentation. Using 18O-labeled methyl benzoate, the S N2 reaction was found to account for a smaller percentage, 21(±1)%, of the benzoate product. Aromatic ring attack resulted in formation of [M + O − H] − and [M − 2H] −· ions. Although aryl hydrogens accounted for most H 2 +· abstracted by O −·, evidence for abstraction of H arylH alkyl +· and H alkylH alkyl +· was also found. Although present at much lower abundance, dehydrobenzoate, dehydrophenoxy, and C 7H 6 −· ([M − 2H − CO 2] −·) radical anions were also observed. An H aryl/H alkyl exchange associated with formation of the benzoate anion was attributed to an H alkyl abstraction that occurred within the methanol/dehydrobenzoate ion–dipole complex. The [M − 2H] −·, dehydrobenzoate, dehydrophenoxy, and [M − 2H − CO 2] −· ion signals were quenched by reaction with O 2. Conditions required for production of O −· spectra under NICI conditions were also examined.

Analysis of Aldehydes in Water by Head Space-GC/MS.

The concentrations of formaldehyde, acetaldehyde, propionaldehyde, and n-butyraldehyde in water were quantitatively determined by head space-gas chromatography/mass spectrometry (HS-GC/MS). Aqueous aldehydes were treated with o-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBOA) in a sealed vial at 60°C for 60 min. Head space was then analyzed by GC/MS. In comparison with electron ionization (EI) mass spectra, negative chemical ionization (NCI) mass spectra of PFBOA derivatives gave more spectral peaks of structural origin and with simple, characteristic fragmentation patterns. HS-GC/MS is highly sensitive for aqueous aldehydes because it eliminates interference from the water sample. The concentrations of various aldehydes in tap water and commercial mineral water were determined by HS-GC/MS. The following concentration ranges were detected for the individual aldehydes; formaldehyde, not detected (N.D.)-59 µg/l; acetaldehyde, N.D.-260 µg/l; propionaldehyde, N.D.- 0.9 µg/l; and n-butyraldehyde, N.D-0.3 µg/l.

Metabolism of halogenated compounds in the white rot fungus Bjerkandera adusta studied by membrane inlet mass spectrometry and tandem mass spectrometry

Membrane inlet mass spectrometry has been used for the characterization of halogenated organic compounds produced by the fungus Bjerkandera adusta. Using this technique we obtained electron impact-, chemical ionization-, electron capture negative chemical ionization-mass spectra and tandem mass spectra directly from the growth medium. Through this direct analysis of the samples we identified novel bioconversion products and confirmed recently published data on the production of both chlorinated and brominated methoxybenzaldehyde metabolites. Growth profiles of the culture grown on a defined medium showed that the production of secondary metabolites starts after approximately 6 days and reaches maximal concentrations of 25-250 muM after 15-20 days. Although delayed, the production of secondary metabolites paralleled a depletion of glucose from the medium and stopped shortly after all glucose had been consumed. Experiments in which fluoro- and bromo-labeled 4-methoxybenzaldehydes were added to the medium at day 8 showed biotransformation of these compounds into chloro-3-fluoro-4-methoxy-benzaldehyde and chloro-3-bromo-4-methoxybenzaldehyde, respectively. No dichlorinated products were observed, suggesting that halogenation takes place only at the meta position on the 4-methoxybenzaldehydes. These experiments are the first to bring direct evidence of a halogenation mechanism, where the enzymatic attack takes place directly on the 4-methoxybenzaldehyde intermediates. (c) John Wiley & Sons, Inc.

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study.

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.

Synthesis and characterization of nitrated [60]fullerene derivatives

A synthetic method for the preparation of monodisperse hexanitro[60]fullerenes 16 was developed. The use of 16 as a reactive precursor in the synthesis of organo-amino derivatives of C60 was also demonstrated. The allylic tert-nitro moieties in hexanitro[60]fullerenes were found to be excellent leaving groups for nucleophilic substitutions by amino nucleophiles, such as anilines, leading to the formation of hexaanilino[60]fullerenes. Negative ion desorption chemical ionization mass spectra (DCI–-MS) of both hexaanilino[60]fullerene and hexanitroso[60]fullerene, a hydride-reduced product of 16, were utilized for substantiation of the number of nitro groups per C60 in 16. Detection of the molecular ion of C60(NO)6 at m/z 901 was correlated to the composition of its parent compound 16, as hexanitro[60]fullerenes containing 6 nitro addends per C60 cage.

Discrimination of structural isomers of chlorinated phenols in waters using gas chromatography–mass spectrometry in the negative chemical ionization mode

The analysis and identification of structural isomers of mono-, di- and trichlorophenols is reported. The fragmentation of the phenols was examined by GC–MS in both electron impact (EI) and negative chemical ionization (NCI) modes, using methane as reagent gas. The ability of NCI to discriminate these isomeric compounds from differences in relative intensities for selected peaks is demonstrated. 3- and 4-chlorophenols have similar retention times; however, they can still be discriminated because their negative mass spectra are rather different. In dichlorophenols, the presence of one chlorine atom in the ortho position decreases their retention time and the relative intensity of the fragment ion at m/ z 140. The NCI mass spectra for trichlorophenols are different from the rest, particularly for the m/ z value corresponding to the chlorine atom. Tetra- and pentachlorophenols were also studied and sequential losses of Cl observed. An automatic solid-phase extraction system can optionally be used to preconcentrate chlorophenols in waters prior to determination at legally established toxic levels.

Electrospray ionization tandem mass spectrometry collision-induced dissociation study of explosives in an ion trap mass spectrometer

Electrospray ionization (ESI) tandem mass spectrometry collision-induced dissociation (CID) fragmentation processes of a series of nitroaromatic, nitramine and nitrate ester explosives were studied in the negative-ion mode using daughter-ion, parent-ion and neutral loss scans. 2,4,6-Trinitrotoluene (TNT) was characterized by loss of OH, NO and NO2. 1,3,5-Trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) were characterized by loss of CH2NNO2, NNO2, NO2 and N2O. 2,4,6,N-Tetranitro-N-methylaniline (tetryl) and its hydrolysis product, N-methylpicramide, showed losses of NO2, HNO2 and NNO2. Pentaerythritol tetranitrate (PETN), glycerol trinitrate (nitroglycerin) and ethylene glycol dinitrate (EGDN) were characterized by loss of CH2NO2, CH2NO, CHNO2, ONO2, NO2 and NO. Similarities were found between ESI and negative chemical ionization mass spectra as well as between their CID fragmentation processes. Detection limits of TNT, tetryl, PETN, RDX and HM were found to be in the 5–10 pg range. © 1997 John Wiley & Sons, Ltd.

Discrimination of structural isomers of amphetamine using carbon dioxide negative-ion chemical ionization mass spectrometry

The negative‒ion chemical ionization mass spectra of a group of structural isomers of amphetamine have been studied using carbon dioxide as the reagent gas. Characteristic and reproducible differences are observed for each member of the set implying that this technique offers a means of distinguishing among groups of amphetamine isomers. Characteristic adducts to the molecular ion are observed in the form (M–[H]+[O]) and (M–[H]+[CO2]). Descriptions of some fragments are given based on the mass spectral behaviour of a set of analogue compounds and the results of oxygen-18 labelled carbon dioxide reagent gas experiments. Contents of the carbon dioxide plasma and their impact on various analytes is also discussed.

Use of Chemical Ionization in Multianalysis Gas and Liquid Chromatography Combined With a Single Mass Spectrometer for the Ultra-trace Level Determination of Microcontaminants in Aqueous Samples†

An automated system that comprises a single mass spectrometer (MS) in combination with gas (GC) and liquid chromatography [LC; particle beam (PB) interface] has been used for the trace-level detection and identification of contaminants in water samples. The analytes were enriched by on-line solid-phase extraction (SPE). In the present study, the potential of negative chemical ionization (NCI) detection in this so-called multianalysis system was explored. Attention was devoted to the enhancement of selectivity and sensitivity as well as to the additional spectral information obtained for the identification of unknown compounds.Nine chlorinated pesticides representing three major groups, i.e., triazines, anilides and organophosphorus pesticides, were used as test compounds. Among the three reagent gases used for NCI, isobutane, methane and ammonia, methane gave the best results. For six of the nine pesticides, a 3- to 30-fold increase in sensitivity was observed in the NCI mode as compared with the electron impact (EI) mode. As expected, the NCI mass spectra showed little fragmentation. Electron capture appears to be the dominant ionization mechanism.In order to study the potential of the total on-line SPE–LC/GC–MS set-up, the pesticides were spiked to tap and surface water samples. The detection limits obtained in the NCI (full-scan) mode ranged from 0.1–3 ng l–1 for GC–MS and 50 to 200 ng l–1 for LC–PB–MS for 100-ml tap water samples. The potential of NCI–MS was demonstrated by the identification of several unknown microcontaminants in a river water sample.

Pentafluorobenzyl derivatives for the gas chromatographic determination of hydroxy-polycyclic aromatic hydrocarbons in urban aerosols

A method for the analysis of hydroxy-substituted polynuclear aromatic hydrocarbons (hydroxy-PAHs), using gas chromatography with electron-capture (ECD) and mass spectrometric (MS) detectors, is described. Pentafluorobenzyl bromide (PFBBr) was used as derivatizing agent for the hydroxy-PAHs. Optimization of the derivatization conditions was performed, and electron impact and negative ion chemical ionization mass spectra were studied. Detection limits ranged 0.01 to 3.3 pg in ECD and negative ion chemical ionization mode (NICI)-SIM-MS values that allowed the determination of these compounds in environmental samples. Samples of air particulate matter were collected for the analysis of hydroxy-PAHs. The concentrations found for 5-hydroxyindol, 2-nitro-1-naphtho, 2-hydroxy-1,4-napthoquinone and 2-hydroxy-9-fluorenone ranged between 5 and 189 pg/m 3.

Positive and negative ion mass spectrometry of ten xanthine derivatives and their rapid clean-up with Sep-Pak C 18 cartridges from biological samples

Positive ion electron impact (PIEI), positive ion chemical ionization (PICI) and negative ion chemical ionization (NICI) mass spectra are presented for ten xanthine derivatives; and each fragmentation pathway has been analyzed. In the PIEI mode, molecular ions were generall intense and constituted base peaks in five compounds. Peaks at m z 42 (NCO) appeared in all compounds; fragment cations at m z 55, 68 (or 67) and 82 were observed in many compounds. In the PICI mode, all drugs showed intense [M+H] + quasi-molecular peaks together with small peaks at m z M+C 2H 5 and M+C 3H 5; fragment peaks at m z 44, 58, 72 and/or 84 (or 86) were also observed. In the NICI mode, [M−H] − quasi-molecular peaks appeared in nine compounds and constituted base peaks in five compounds; adduct anions at m z M+32 and/or M+C 3H 7, and fragment anions at m z 42, 165 and/or 179 were also observed in many compounds. Detection limits for total ion monitoring of the drugs in the PIEI, PICI and NICI modes were 2.2–10 ng, 11–28 ng and 7.8–14 ng on column, respectively. Xanthine derivatives present in human plasma or urine could be rapidly extracted by use of Sep-Pak C 18 cartridges with chloroform/methanol as elution solvent; recovery of the drugs from the plasma and urine was > 75%. They were also detected by capillary gas chromatography (GC) with both flame ionization detection (FID); their limits were 1.6–8.3 ng on column.

Negative ion chemical ionization and collisionally activated decomposition mass spectra ofO-2,3,4,5,6-pentafluorobenzyloxime derivatives of prostaglandins

Prostaglandin E1, prostaglandin E2, prostaglandin E3, 6-oxo-prostaglandin F1α, 1-carboxy-rioprostil and rioprostil were derivatized to the pentafluorobenzyloxime/trimethylsilyl ether/methyl ester and pentafluorobenzyloxime/trimethylsilyl ether (rioprostil) respectively. In the high-mass region, except for the 6-oxo-PGF1α, derivative, negative ion chemical ionization (methane) mass spectra show an intense [M - HF]−. ion. Collisionally activated decomposition mass spectra (0.2 Pa argon collision gas pressure, 15 eV collision energy) of this parent ion ([P]−.) of the syn and anti oxime isomers are quite different. The syn isomers have intense [P  (C1–C7)]− and [C6F4CH2O]− daughter ions, while the most abundant peaks in the spectra of the anti isomers are [P  OH  TMSOH]−, [P  OH  2TMSOH]− and [(C9–C10)  HF]−. Negative ion chemical ionization mass spectra of 6-oxo-prostaglandin F1α derivatives have intense [M  HF  (CH3)2SiCH2]− ions. Most prominent daughter ions are [P  (C1-C5)]− and [P - 2HF  H  (C1–C5)]−.

Correlation between electron capture negative chemical ionization mass spectrometric fragmentation and calculated internal energies for polychlorinated biphenyls

Correlations between molecular structure and fragmentation observed in electron capture negative chemical ionization mass spectra (moderator gas = methane) of 49 selected tetrachlorinated, pentachlorinated, and hexachlorinated biphenyls have been investigated by using molecular modeling. The semiempirical general molecular orbital program MOPAC was used to calculate molecular properties for biphenyl and the 209 polychlorinated biphenyls. The mass spectrometric ionization and fragmentation processes were found to be linked to the number of chlorine atoms present on the biphenyl, and to the number of those chlorine atoms in the ortho (2, 2′, 6, and 6′) positions. The intensity of molecular ions increased with the number of chlorine atoms present, but this was counteracted by enhanced fragmentation as the number of ortho position chlorine atoms increased. The molecular parameters that were most closely linked with the number of ortho chlorine atoms were the twist angle between the phenyl rings and the energy of the lowest unoccupied molecular orbital (LUMO). It is suggested that fragmentation occurs when the energy of the ionizing electron exceeds the energy difference between the LUMO and LUMO + 1 orbitals.