Fast Atom Bombardment Mass Spectra Research Articles

Optimization of fast atom bombardment (FAB) mass spectra of arsenobetaine and arsenocholine

AbstractOptimized FAB mass spectra of arsenobetaine and arsenocholine may be obtained when the matrices glycerol and thioglycerol are used.

Fast atom bombardment mass spectra of dihydroxybenzenes: Formation of radical cation adduct between sample and matrix

AbstractUnder fast atom bombardment, dihydroxybenzenes form predominantly the M+· and [M + Matrix]+· ions. The second field‐free region metastable decomposition of the [M + Matrix]+· ion involves the loss of a neutral molecule of the matrix. In the case of the hydroquinone–matrix adduct ion, elimination of both the matrix and hydroquinone are observed. Surprisingly, alkali metal cationization also leads to the formation of abundant radical cations in which the acidic hydrogens have been replaced with alkali metal. The degree of this exchange varies among the isomeric compounds. The facile formation of radical cations and their adducts appears to be due to various factors such as the ionization potentials, redox potentials and the proton affinities of the dihydroxybenzenes and the analyte‐matrix interactions.

Negative‐ion fast atom bombardment tandem mass spectrometry of sodium salts of monensins and related compounds

AbstractThe negative‐ion collisionally induced dissociation fast atom bombardment mass spectra of sodium salts of monensins A and B, their 3‐O‐demethyl derivatives, laidlomycin and 26‐deoxylaidlomycin are reported. The nature of the R3 substituent appears to be important for the formation of sodium‐containing product ions. Fragment ion series observed in the mass spectra of the [M − H]− ions of monensins are characterized by alkali metal retention. In contrast to monensins, the product ions observed in the corresponding spectra of laidlomycins are sodium free. The affinity of monensins to alkali metals is a useful feature that may be used for the structure determination of unknown monensins, their metabolites and derivates. The structure of a novel natural monensin was elucidated based on its mass spectrometric behaviour.

Fast atom bombardment, frit fast atom bombardment and electrospray ionization mass spectrometric study of organic salts C2+ 2X−: Matrix and anion effects

AbstractThe fast atom bombardment (FAB), frit‐FAB and electrospray ionization mass spectra of bis‐ammonium salts, C2+ 2X−, were compared. The most informative spectra were the FAB mass spectra with m‐nitrobenzyl alcohol as matrix and the Frit‐FAB mass spectra. The nucleophilic character of the iodine anion was established.

Oligosaccharide characterization using collision‐induced dissociation fast atom bombardment mass spectrometry: Evidence for internal monosaccharide residue loss

AbstractThe protonated and sodium cationized pseudomolecular ions of a series of reducing and non‐reducing oligosaccharides possessing aldopentopyranosyl, 6‐deoxyaldohexopyranosyl, ketohexofuranosyl, 4‐O‐methyl glucuronopyranosyl methyl ester and N‐acetyl 2‐deoxyglucopyranosylamine units were studied using collision‐induced dissociation (CID) fast atom bombardment (FAB) mass spectrometry. The CID spectra of the [M + H]+ ions provide information about the sequence of the monosaccharide units, while dissociation of the [M + Na]+ ions by two‐bond ring cleavage processes gives rise to fragment ions which allow differentiation of 1 → 2 and 1 → 4 linkages. The influence of the structure of the constituent monosaccharides on the dissociation of the [M + H]+ and [M + Na]+ ions is discussed. An unusual type of fragmentation, which we suggest involves the elimination of internal monosaccharides residues, has not only been observed in the FAB mass spectra but also in the unimolecular decomposition and CID spectra of both [M + H]+ ions and oxonium ions from several oligosaccharides containing monosaccharide residues with different masses.

Liquid secondary ion mass spectra and fast atom bombardment mass spectra of diquaternary pyridinium oxime salts

AbstractPositive‐ion mass spectra of diquaternary pyridinium oxime salts were measured using fast atom bombardment and liquid secondary ion mass spectrometry in different laboratories to establish both the characteristic behavior and the spectral variability of this class of compounds. Molecular ions observed in these mass spectra include the one‐electron reduced doubly charged cation, the deprotonated double charged cation and the anion‐reduced doubly charged cation. Common fragment ions include the products of simple cleavages along the aliphatic bridge between the heterocyclic rings. Concomitant loss of hydrogen and cyclization of the bridge can occur, along with losses of OH, NOH and CHNOH from various fragment ions. A nitrobenzyl alcohol matrix generally gave superior results to glycerol and thioglycerol in all laboratories, although the use of additive surfactant acids such as p‐toluenesulfonic acid or camphorsulfonic acid in glycerol could provide useful results.

Identification of Microbial and Rat Metabolites of Triflusulfuron Methyl, A New Sugar Beet Herbicide

Triflusulfuron methyl (methyl 2-[[[[[4-(dimethylamino)-6-(2,2,2-trifluoroethoxy)-1,3,5-triazin-2-yl]amino]carbonyl]amino]sulfonyl]-3-methylbenzoate) is a new selective low use rate sulfonylurea herbicide for the control of many broad-leaved weeds and grasses in sugar beets. Our studies show the compound undergoes rapid microbial metabolism using Streptomyces griseolus and that a mixture of similar metabolites is excreted by triflusulfuron methyl-dosed rats. Nine intact sulfonylurea metabolites were tentatively identified in microbial studies, and five of these were later identified in urine or feces of rats dosed with radiolabeled triflusulfuron methyl. Metabolic reactions include alkyl and/or aryl oxidation, N-dealkylation, and ester hydrolysis. All identifications were made using liquid chromatography/mass spectrometry (LC/MS) with fast atom bombardment (FAB) ionization. FAB mass spectra gave strong protonated molecular ions and structurally useful fragment ions of these extremely thermally labile metabolites

Comparison of electrospray mass spectrometry with other soft ionization techniques for the characterisation of cationic π-hydrocarbon organometallic complexes

Electrospray (ES) mass spectrometry provides a convenient method for the characterisation of a wide range of π-hydrocarbon complex salts of the general types [FeCp(η-arene)]BF 4, [M(CO) 3(η-C 7H 7)BF 4 (MCr, Mo, W), [Fe(CO) 2L ( η 5-dienyl)]BF 4 L  CO or PPh 3; dienyl  C 6H 7, 2-MeOC 6H 6, or C 7H 9), [CpFe(CO) 3] PF 6 and [CpFe(CO) 2( η-C 2H 4)]BF 4. At low skimmer voltages (20 V), principal (molecular) ions are generally the only observed species. For the arene complexes, [FeCp( η-arene)]BF 4, high skimmer voltages (80–135 V) are required before fragmentation is observed. However, for the carbonyl containing cations, moderate skimmer voltages (40–55 V) also give rise to [MCO] +,[M2CO] + and [M3CO] + ions. Very similar behaviour is observed with phosphonium and imidazolium adducts of the type [Fe(CO) 3(η 4-diene. Nuc)] + ( diene  C 6 H 7 or C 7H 9; Nuc PPh 3 or Im) and [CpFe(CO) 2( η 1-C 2H 4·PPh 3)] +. comparison with fast atom bombardment (FAB) and field desorption (FD) mass spectra for the same complex salts indicates that fragmentation decreases along the series FAB > ES > FD, and that ES mass spectrometry is the most convenient and informative of the three soft ionization techniques.

Possible involvement of dihydrofructosazine in the DNA breaking activity of D-glucosamine.

Dehydrochlorination of D-glucosamine (2-amino-2-deoxy-D-glucose) hydrochloride with an anion exchange resin made its DNA breaking activity in plasmid pBR322 much higher, especially in the presence of Cu2+. The sample of anion exchanger-treated D-glucosamine hydrochloride, i.e., HCL-free D-glucosamine sample, showed an absorption maximum at 274 nm on the UV absorption spectrum in water as seen in the case of fructosazine [2,5-bis(D-arabino-tetrahydroxybutyl)pyrazine] one of the dimers of D-glucosamine. On a positive-ion fast atom bombardment (FAB) mass spectrum, the sample showed an ion peak at m/z 323 as a base peak, corresponding to dihydrofructosazine [2,5-bis(D-arabino-tetrahydroxybutyl) dihydropyrazine], which was a precursor of fructosazine, as well as those of D-glucosamine itself (m/z 180) and fructosazine (m/z 321). The DNA strand breaking activity of HCL-free D-glucosamine sample was directly proportional to the peak intensity of m/z 323 ion, while the DNA breaking activity of fructosazine was much weaker than that of HCL-free D-glucosamine sample. 2,5-Dihydro-3,6-dimethylprazine and 2,3-dihydro-5,6-dimethylpyrazine having a dihydropyrazine skeleton the same as dihydrofructosazine showed the same extent of DNA strand breaking activity as did the HCL-free D-glucosamine sample. These results indicated that dihydrofructosazine produced during the dehydrochlorination is closely involved in the DNA breaking activity of HCL-free D-glucosamine sample.

Some Characteristics of Gas-Phase Fast Atom Bombardment Ionization Mass Spectrometry: Chromium Hexacarbonyl and Trolox.

Gas-phase fast atom bombardment (GFAB) mass spectra of the chromium hexacarbonyl molecule were compared with its charge-exchange ionization (CEI) mass spectra. It was found that the fragmentation pattern of chromium hexacarbonyl ions obtained by He-CEI mass spectrometry most resembles those measured in GFAB, and so it seems that energy deposition during GFAB implies involvement of a resonance-like energy transfer from fast atoms and may be similar or higher than that in He-CEI reaction. No great difference was observed in GFAB mass spectrum for a variety of fast bombarding particles including He, Ar, Xe, Cs, and isobutane. A high pressure GFAB mass spectrum of trolox measured using a Cs beam demonstrated its reactive nature that exchange reaction between hydroxy protons and Cs+ ions seems to take place in gas phase for the molecule and its neutral fragments while a Cs-FAB mass spectrum measured under a relatively low sample gas pressure showed only a fragmentation pattern characterized by a high abundance of fragment ions. Since Cs is only an alkali metal among fast bombarding particles, its chemical nature may be responsible for the observed reactivity with the target molecule.

Fast atom bombardment (FAB) mass spectrometry of diterpene resin acid derivatives

The behaviour of methyl dehydroabietate and its ring C-substituted derivatives has been investigated by fast atom bombardment (FAB) mass spectrometry conditions. Similar FAB mass spectra were obtained in a 3-nitrobenzyl alcohol matrix using argon or xenon as the target gas, which has been attributed to the hydrophobic character of these compounds. Significant [M ‐ H] + , M +• and [M + H] + peaks and minor abundant [M ‐ 3H] + , [M ‐ 2H] +• and [M + 2H] +• ions have been observed to occur in the spectra. The intense M +• peaks generally observed have been rationalised in terms of the relatively aprotic and hydrophobic character of the matrix 3-nitrobenzyl alcohol and the hydrophobic nature of the compounds studied. The molecular ion represents the base peak in the molecular mass region of the amino abietates when 3-nitrobenzyl alcohol or triethyltetramine are used as matrices, presumably reflecting the stability of these radical cations. The relatively aprotic character of the matrix has been suggested to favour the ionization to M +• ions of the amino derivatives. The electrophilic nitro groups and/or a proton acceptor carbonyl group, have been found to play an important role in the formation of [M + H] + with respect to M +• ions. The enhanced abundance of [M + H] + with respect to M +• ions, when HCl was added to the matrix, as well as in a thioglycolic matrix, has been suggested to derive from a contribution of solution chemistry for the compounds bearing one to two unsubstituted amino groups. An important role played by the common hydrocarbon skeleton has been suggested to account for the significantly abundant [M ‐ H] + ions observed.

Thermal degradation of O‐acyl oximes under electron impact ionization conditions

AbstractThermal degradation of O‐acyl oximes under electron impact ionization (EI) conditions has been examined. The EI mass spectra gave fragment ions originating from thermal degradation, as well as molecular ions M+· and normal fragment ions due to unimolecular decomposition of the M+· ions. The fragment ions due to thermal degradation of O‐acyl oximes were identified by using fast‐atom bombardment (FAB) mass spectrometry with a liquid matrix together with the collision‐induced dissociation (CID) technique. While the FAB mass spectra of O‐acyl oximes gave, preferentially, M+· ions together with some characteristic fragment ions, as well as the molecular related ions [M+H]+ and [M−H]+, the spectra showed little evidence of the fragment ions which may originate from thermal degradation, under EI conditions. The CID spectra of selected M+· ions formed by electron impact also showed little of such fragment ions. The thermal degradation was directly confirmed by measuring the FAB mass spectra of O‐acyl oximes that had been heated in a sealed sample tube.

Formation of (M-H)- Ions under Fast-atom Bombardment Conditions: Which is reflected, gas-phase or solution chemistry?

The formation of deprotonated molecules [M-H]- of Trolox having a carboxyl and a phenolic hydroxyl group and the derivatives, under fast-atom bombardment (FAB) conditions, has been examined from the viewpoint of proton-transfer reaction in gas-phase or solution. The negative-ion FAB mass spectra of the derivatives strongly suggested that deprotonation mainly occurs on the carboxyl group through the electrolytic dissociation in matrix solution. The use of higher proton acceptability matrices such as glycerol, pentamethylene glycol, and diethanolamine was favorable for the detection of [M-H]- ions of a Trolox methyl ester, while the use of lower proton acceptability matrices such as m-nitrobenzyl alcohol and dithiothreitol was unfavorable for the [M-H]- formation. While the result obtained suggested that the formation of [M-H]- ions reflects the gas-phase basicities of matrices used, the results from the negative-ion FAB mass spectra of the Trolox methyl ester and α-tocopherol suggested that the [M-H]- formation reflects solvation states such as hydrophobic and hydrophilic interactions between analyte and matrix molecules in matrix solution. The site of deprotonation of the compounds used has been examined by using collision-induced dissociation (CID) technique, and it was shown that the CID characteristics of [M-H]- ions depend markedly on the site of deprotonation. It was presumed, consequently, that the [M-H]- ion formation under FAB conditions is governed by gas-phase thermochemistry and/or solution chemistry according to the nature of analyte and matrix used.

Fast atom bombardment mass and tandem mass spectra of protonated and alkali cationized aldobiouronic and pseudoaldobiouronic acid per‐O‐methyl derivatives

AbstractThe positive‐ion fast atom bombardment mass spectra of permethylated aldo‐ and pseudoaldobiouronic acids can be used to distinguish these classes of compounds. The collisional‐induced dissociation spectra of the [M + H]+ ions show fragment ions resulting from glycosidic bond cleavage and successive losses of methanol molecules. These spectra together with those of the [M + H  MeOH]+ oxonium ions allow the identification of the type of interglycosidic linkage. Collisional activation of the relatively stable [M + Na]+ ions show many fragmentations which are common to alkali cationized permethylated saccharides. Moreover, fragment ions resulting from two‐bond ring cleavage processes yield additional information with respect to the linkage between the hexose and uronic acid units.

Fragmentation characteristics of neuropeptides related to chromogranin B and proenkephalin B using fast atom bombardment and collision-induced dissociation

This study deals with the mass spectral characterization of selected neuropeptides related to chromogranin B and proenkephalin B precursor proteins using fast atom bombardment (FAB) ionization in combination with low- and high-energy collision-induced dissociation. Fragmentation pathways were investigated using linked scan and tandem mass spectrometric techniques. First-order FAB mass spectra and product ion spectra of [M+H]+ ions are discussed and analysed for structure-specific information. In the high-energy product ion spectra, abundant y and c ions are found to be indicative of the presence of proline and threonine residues, respectively. With regard to side chain specific ions, diagnostic d and w ions are found, which support the presence of leucine, glutamic acid and glutamine at specific positions in the amino acid sequence.

Formation and collision-induced dissociation of adduct ions [matrix + C] + (C  Li, Na, Cs and NH 4) produced under fast atom bombardment conditions

The formation of adduct ions of matrices B with organic/metallic cations C +, [B + C] + (C  Li, Na, Cs and NH 4), under fast atom bombardment (FAB) conditions has been examined. The cation affinity (CA) for various matrix materials, glycerol, thioglycerol, dithiothreitol, m-nitrobenzylalcohol and diethanolamine, was evaluated from the positive-ion FAB mass spectra obtained for the salts LiCl, NaCl, CsCl or NH 4Cl added to matrix B. The order of the CA of matrices for relatively small cations Li + and Na + was in accordance with that of the proton affinity (PA) of the matrices used. The collision-induced dissociation (CID) spectra of [B + H] + and [B + C] + ions have been obtained. The PA differences between matrix B and ammonia (NH 3) molecules were roughly estimated from the CID spectra of [B + NH 4] + ions. The CID spectra of [B + C] + ions, which have different dissociation windows from [B + H] + ions, were analyzed by proposing multidentate-binding structures of the adduct ions. Some dissociations of [B + C] + ions could be explained by charge-remote fragmentations. The results obtained suggest that the binding energy for the coordination complex (B⋯C +) can be evaluated from the CID patterns.

Improvement of Chemical Analysis of Antibiotics. Part XIX1: Determination of Tetracycline Antibiotics in Milk by Liquid Chromatography and Thin-Layer Chromatography/Fast Atom Bombardment Mass Spectrometry

A precise liquid chromatographic (LC) determination with high sensitivity and a reliable mass spectrometric (MS) confirmation were established for the determination of tetracycline antibiotics (TCs) in milk. The determination of the TCs was based on C18 cartridge cleanup followed by LC separation. Recoveries of TCs from milk fortified at 20 ppb were 73.0-81.8%, and coefficients of variation were 2.6-4.6%. With this method, concentrations of oxytetracycline and tetracycline as low as 10 ppb and chlortetracycline and doxycycline as low as 20 ppb were determined readily. Thin-layer chromatography (TLC)/fast atom bombardment (FAB) MS with a condensation technique was used to confirm TCs in milk. After the C18 cartridge cleanup, separation on a C8 TLC plate, and application of the sample condensation technique, FAB mass spectra were measured. TCs in milk at 50 ppb were reliably confirmed by TLC/FABMS.

Characterization and differentiation of diglycosyl flavonoids by positive ion fast atom bombardment and tandem mass spectrometry

This study shows that fast atom bombardment (FAB) in combination with collisional activation and tandem mass spectrometric techniques is useful for the characterization of, and the differentiation between, O-diglycosyl, O-C-diglycosyl and di-C-glycosyl flavonoids. A quick differentiation between the three types of glycosyl flavonoids is possible by simply examining FAB mass spectra. Low-energy product ion spectra of [M+H]+ ions have been used for determining the carbohydrate sequence in O-diglycosyl flavonoids and characterizing the terminal monosaccharide in O-C-diglycosyl flavonoids. The data obtained for per-O-deuterated precursor ion species of O-diglycosyl flavonoids indicate that O-linked hydrogen atoms are involved in the formation of Yn+ ions. High-energy product ion spectra of [M+H]+ ions enable further characterization and differentiation of isomeric di-6,8-C-glycosides.

Fast-Atom Bombardment Mass Spectrometry of Phosphonopeptides

Abstract The fast-atom bombardment mass spectra of phosphonopeptides, having an α-aminoalkanephosphonic acid as the acid-terminal residue, have been recorded using a glycerol matrix and a primary beam of xenon atoms operating at 6–8 kV. The identities of selected ions were confirmed by exact mass measurements. All peptides gave characteristic pseudomolecular ions, [MH]+, which appeared as the base peak in many cases. Protonated dimers, [2M + H]+, higher clusters, and ions resulting from association with glycerol were also observed, particularly in the case of dipeptides. Fragmentation occurred mainly by the elimination of α-amino-carboxylic acid residues, via peptide bond cleavage with hydrogen transfer, and by elimination of phosphorous acid from the aminophosphonic moiety. In addition, evidence was seen in certain cases for amide-bond fission with formation of an acylium ion which subsequently lost carbon monoxide.

Structural and substituent effects on [M]+.vs. [MH]+ formation in fast atom bombardment mass spectra of simple organic compounds

AbstractThe peak intensity ratios of [M]+. vs. [MH]+ were measured in the fast atom bombardment (FAB) mass spectra of readily available test compounds with 3‐nitrobenzyl alcohol as the matrix. For simple aromatic amines, the ratio increases as the ionization energy of the substrate decreases. 4‐Substituted benzophenones showed preferential formation of [MH]+ ions, regardless of the nature of the substituents. This is probably due to the fact that the benzophenoes have carbonyl groups which can form hydrogen bonds with the matrix molecule. The peak intensity ratio is roughly proportional to the Hammett σ+. Among 4‐substituted biphenyls, both bromo and chloro substituents afforded abnormally high peak intensity ratios. The effects of the substituents in these compounds are discussed semi‐quantitatively in terms of the Hammett correlation and the hard and soft acids and bases principle. The mechanism of ion formation in FAB and chemical ionization (CI) ion sources appeared to be different because some of the compounds studied showed an intense [M]+. peak with a relatively weak [MH]+ peak in FAB spectra but exhibited a strong [MH]+ peak in ordinary CI spectra.