FAB Matrix Research Articles

Use of protic and aprotic solvents of high volatility as matrices in analytical low‐temperature fast‐atom bombardment mass spectrometry

Low-temperature fast-atom bombardment mass spectrometry (LT-FAB-MS) can extend the range of applications of FAB-MS significantly. Solvents of high volatility, either protic or aprotic, can be used as matrices for FAB-MS. For this purpose, the solution of the analyte in the respective solvent is frozen in liquid nitrogen on the FAB probe tip prior to measurement. Thus, one important limitation for selecting the FAB matrix is circumvented. Instead, solvent characteristics optimized to meet the requirements of the analyte are becoming the crucial parameter for the matrix of choice. The potential of this method of sample preparation is demonstrated by the use of methanol as a matrix for LT-FAB-MS of γ-cyclodextrin, dichloromethane for porphyrins and a ruthenium carbonyl–porphyrin complex and toluene for [60]fullerene. Copyright © 1998 John Wiley & Sons, Ltd.

Use of protic and aprotic solvents of high volatility as matrices in analytical low-temperature fast-atom bombardment mass spectrometry

Low-temperature fast-atom bombardment mass spectrometry (LT-FAB-MS) can extend the range of applications of FAB-MS significantly. Solvents of high volatility, either protic or aprotic, can be used as matrices for FAB-MS. For this purpose, the solution of the analyte in the respective solvent is frozen in liquid nitrogen on the FAB probe tip prior to measurement. Thus, one important limitation for selecting the FAB matrix is circumvented. Instead, solvent characteristics optimized to meet the requirements of the analyte are becoming the crucial parameter for the matrix of choice. The potential of this method of sample preparation is demonstrated by the use of methanol as a matrix for LT-FAB-MS of γ-cyclodextrin, dichloromethane for porphyrins and a ruthenium carbonyl–porphyrin complex and toluene for [60]fullerene. Copyright © 1998 John Wiley & Sons, Ltd.

Negative-ion fast atom bombardment mass spectrometry of sulfonylurea herbicides

Seven sulfonylurea herbicides were studied using negative-ion fast atom bombardment mass spectrometry (FAB-MS). The spectra were characteristic of the structure of the examined herbicides with fragmentation at the sulfonylurea bridge representing both aromatic moieties. The fragmentation pattern was established based on the FAB- B/E mass spectrometry/mass spectrometry linked-scan spectra. Background-subtracted negative ion FAB-MS spectra of the herbicides exhibit [M‐1] ‐ peaks and their fragmentation products. Application of triethylenetetramine as a FAB matrix resulted in enhanced fragmentation. The 3-nitrobenzyl alcohol FAB spectra typically exhibited high-abundance [M‐1] ‐ peaks and fewer fragment

The interpretation of collision‐induced dissociation tandem mass spectra of peptides

The introduction of fast atom bombardment (FABJ ionization mass spectrometry (MSJ ( 1 ) in the early 1980s enabled mass spectrometrists to obtain molecular weights of many nonvolatile molecules, including p e p tides comprising 10-20 amino acids, and, by the mid-1980s. small proteins could be desorbed and their molecular weights measured (2-7). FAB (here used generically to include fast atom as well as ion bombardment of the sample dissolved in a liquid matrix such as glycerol), being a ”soft ionization” technique, produces little or no fragmentation of protonated peptide molecules. This characteristic is, certainly, desirable, because it allows for the unambiguous assignment of molecular weights, even in multicomponent mixtures. Nevertheless, fragmentation of a molecule, after ionization in the mass spectrometer, can be used to obtain structural information, often completely and uniquely, and for decades mass spectra of thousands of compounds have been acquired, interpreted, and cataloged. Peptides consisting of as few as several amino acids are nonvolatile and, often, thermally labile and cannot be introduced into the mass spectrometer in the gas phase without prior derivatization. Derivatized peptides have been successfully fragmented, primarily using electron impact (El) ionization, and their amino acid sequence determined (8-1 3). sometimes with the assistance of computer programs ( 1 4). Complex mixtures of protein enzyme digests, often followed by partial acid hydrolysis, were derivatized and introduced into the mass spectrometer after fractionation with a gas chromatograph (GC). The El spectra were used to obtain amino acid sequences for the peptides, which were subsequently combined to arrive at the sequence of the protein. Peptide fragments, which sometimes are produced during FAB ionization, can be correlated to the peptide amino acid sequence ( 15-20). The abundance of such fragment ions, however, is quite low compared with the ions due to the protonated molecule. In addition, in order to obtain reasonably abundant fragment ions, a fairly concentrated sample is required, and even then large peptides (e.9.. longer than 10 amino acids) do not fragment efficiently. Also, at lower mass (e.g., below m/z 500). fragment ions are usually difficult to identify, due to the FAB matrix background, and, of course, in mixtures more than one peptide usually fragments, thereby increasing the difficulty of fragment ion assignments to particular precursor ions. The advent of tandem mass spectrometry (MS/MS) (2 1-23) made it possible to analyze complex peptide mixtures (24-34) without the need to separate the individual components, because a mass window narrow enough to exclude all but one of the mixture components can be specified

Characterization of a complex mixture of ceramides by fast atom bombardment and precursor and fragment analysis tandem mass spectrometry

Fast atom bombardment, precursor and fragment ion analysis mass spectrometry were employed to characterize the fatty acid and long-chain base composition of a complex ceramide mixture prepared from beef brain lipids. Precursor ion analysis of a sphingenine-specific fragment allowed selective recognition of ceramides with different fatty acids, some of which escaped undetected in the source spectra owing to background contamination of the FAB matrix. The use of a triple quadrupole yielded far better results than linked scanning on a sector mass spectrometer, owing to unit mass resolution of the precursor ions, which allows discrimination of saturated from unsaturated acids with the same number of carbon atoms. The composition of the mixture of linked fatty acid was derived from the intensity of the molecular species both in the source and in the precursor spectra, and was compared with that obtained by capillary gas chromatography of the released fatty acid methyl esters. Some discrepancy between the values obtained with the two techniques can be attributed to very different surface activity of the short- and long-chain fatty acids. Analysis of the fragment ions following collision-induced decomposition of cationized species allowed localization of the position of the double bond in a ceramide containing a C-24:1 fatty acyl chain.

A New Postcolumn Addition Method of the Matrix for Microbore Liquid Chromatography/Frit-Fast Atom Bombardment Mass Spectrometry.

In the combination of liquid chromatography (LC)-fast atom bombardment mass spectrometry (FABMS), a new frit postcolumn addition of matrix (frit-PAM) system was designed to overcome the problems such as the diffusion of analytes and the ineffective ionization on FAB probe under the slow mobile phase flow. This system had a coaxial flow of LC effluent and FAB matrix in two separate tubes, and a frit to mix the both flows. The potential of this system was explored in the Frit-FAB LC/MS analysis of the tryptic digest of lysozyme as a test sample. This system can allow to use the mobile phases for the optimum separation in LC and the FAB matrix solution for the optimum ionization of analytes in FABMS, respectively, and can provide a high sensitivity.

Usefulness of fast‐atom bombardment and collision‐activated dissociation linked scan (B/E) mass spectrometry for structural investigation of indole alkaloids

AbstractPositive‐ion fast‐atom bombardment (FAM) mass sspectrometry was used to ionize two indole alkaloids, namely trinervine and its quaternary metho‐salt venecurine containing a hemiketal ring system. Analysis of collision‐activated dissociation spectra by the technique of linked scanning at consltant B/E gave sturcturally useful information. Addition of concentratedf acid to the glycerol matrix yielded glycoside‐type derivatives from both compounds. These studies Provide further examples of an ‘acid effect’ on the protonation site of polyfunlctional molecules along with the possibility of their undergoing chemical mokification in the FAB matrix.

Ion Pairing of Hydrophilic Analytes with Surfactants to Enhance FABMS Spectra

Abstract Recently the use of ion-pairing of inorganic and organic ions to ionic surfactants has been exploited in Fast Atom Bombardment Mass Spectrometry (FAB-MS) in order to increase secondary ion emission. Hydrophilic organic ions, such as 6-aminopenicillanic acid (6-APA), can be selectively ‘bound’ to the surface of a hydrophilic FAB matrix such as glycerol via interaction with an ionic surfactant of opposite charge. Thus, ion-pairing of analyte to surfactant allows for utilization of the surface specificity of FAB. In order to assess the utility and limitations of ion-pairing in FAB, we studied the secondary ion emission characteristics of a cation exchange model system consisting of the quaternary ammonium salt choline chloride (CC), the surfactant octyl sodium sulfate (OSS), and glycerol. Large, weakly solvated ions such as the tetramethylammonium ion of choline readily exchange sodium from sulfonate based cation exchange resins. Cation affinity for sulfate in increasing order is Li+< H+< Na+< NH4 +...

Cationization of organometallo carbonyl compounds by fast ion bombardment

Organodicobalt, organochromium, and organomolybdenum carbonyl complexes have been studied using fast ion bombardment mass spectrometry. It has been found that the addition of cesium iodide to the liquid matrix, m-NBA, can significantly enhance the ability to observed the precursor ions of these organometallics through charge localization. In most cases the [M + Cs] + ions were more abundant than the radical cations M −, the protonated molecules [M + H] +, or the sodium cationized molecules [M + Na] + which were either unobservable or less intense than those treated with the cesium iodide salt solution. The decomposition of the compounds took place primarily through the successive loss of carbonyls from the radical cation with some carbonyl loss observed through the protonated and cationized species. The FAB matrix ions produced when cesium iodide was added to m-NBA also allowed for internal calibration.

Incorporation of tandem mass spectrometric detection to the analysis of peptide mixtures by continuous flow fast atom bombardment mass spectrometry

The ability to acquire structurally informative daughter ion spectra for individual peptides undergoing separation and analysis by continuous flow fast atom bombardment (CF FAB) is demonstrated. To illustrate the potential of this methodology, tryptic and chymotryptic digests of the 29-residue peptide glucagon were analyzed by CF FAB using mass spectrometric and tandem mass spectrometric detection in consecutive analyses. Daughter ion spectra were recorded using B/E linked scans for the major hydrolysis products observed by liquid chromatography/mass spectrometry. The peptide mixtures were separated by gradient capillary high-performance liquid chromatography with the FAB matrix being added post-column using a coaxial flow interface between the column and flow probe. The entire effluent (3 microl min(-1)) was sampled by the mass spectrometer. Results obtained using less than 300 pmol of digested glucagon indicated several advantages to tandem mass spectrometric detection including the ability to confirm identities for products of enzymatic digestion and the potential use of this method for tandem sequence analysis of peptide mixtures.

On‐line combination of supercritical‐fluid chromatography with fast‐atom bombardment mass spectrometry

AbstractStudies on combined supercritical‐fluid chromatography (SFC) using a packed column, with fast‐atom bombardment mass spectrometry (FAB‐MS) are described. The interfacing was successfully carried out by simply coupling a frit interface between the liquid chromatograph (LC) and the mass spectrometer. The interface was equipped with a pneumatic splitter and post‐column addition device delivering FAB matrix material to a release valve which maintained a constant back‐pressure at the column outlet. Using a 1% glycerol solution as a matrix compound in the release valve, the SFC/FAB‐MS combination operates as well as a normal LC/MS instrument. The performance was demonstrated with a mixture of α‐, β‐ and γ‐tocopherol and Triton X‐100 (poly(ethylene glycol) p‐isooctylphenyl ether).

Metalloporphyrins in fast atom bombardment mass spectrometry: implications for processes occurring in the liquid matrix

The use of fast atom bombardment mass spectrometry is investigated as a technique to study a series of porphyrins (H{sub 2}P) and metalloporphyrins (MetP). Rates of demetalation and the redox chemistry of such compounds as well as complex inter- and intramolecular electron-transfer processes are examined. Comparison of the solution chemistry of metalloporphyrins with their behavior in FABMS lead to an understanding of various aspects of the physicochemical events occurring in the FAB matrix. By using FAB matrices with different electronic or acidic properties it is demonstrated that demetalation can occur either by proton displacement or one-electron reduction of the metal. It is also shown that demetalation by protons in FABMS correlates with stability index (S{sub i}) and that the (H{sup +}) in the FAB matrix is {approximately} 2 {times} 10{sup {minus}4} M.

Investigation of porphyrins and metalloporphyrins by fast atom bombardment mass spectrometry

The use of fast atom bombardment mass spectrometry (FAB-MS) to study a series of porphyrins (H 2P) and metalloporphyrins (MetP) was investigated. Methods of sample preparation and choice of a suitable matrix for optimum FAB-MS studies of porphyrins are described. Rates of demetallation and the redox chemistry of such compounds were examined and the solution chemistry of metalloporphyrins was compared with their behaviour in FAB-MS. Such considerations lead to an understanding of various aspects of the physico-chemical events occurring in the FAB matrix. By using FAB matrices with different electronic or acidic properties, it was demonstrated that demetallation can occur either by proton displacement or one-electron reduction of the metal. It was also found that demetallation by protons in FAB-MS correlates with the stability index (S i ). One-electron reductions of Ag(II)P and Cu(II)P were shown to occur via an excited-state intermediate. Consideration of fragmentation and metal ion uptake by two multi-component porphyrins in FAB-MS also confirmed the previously assigned geometry of these compounds.

Fast atom bombardment mass spectrometry of disaccharide polyether polyols

AbstractThe products resulting from the propoxylation of sucrose and lactose under alkaline conditions have been studied using FAB mass spectrometry. Soft desorption/ionization, using fast atoms, was expected to show intense protonated molecules for each component of the reaction mixture, thus allowing the extent of propoxylation to be examined under various conditions. However, it appears that addition of the FAB matrix, namely thioglycerol, prior to mass spectral analysis, resulted in alteration of the analyte via hydrolysis/dehydration, with protonated molecules appearing only for matrix/analyte reaction products, and not the original compounds which were to be examined. The resulting mass spectra, however, provided information regarding the extent of propoxylation and were consistent with results obtained by other researchers examining acetylated sugars using CI‐MS.

Sequence analysis of highly sulfated, heparin-derived oligosaccharides using fast atom bombardment mass spectrometry.

Heparin, a polydisperse, sulfated copolymer of 1----4 linked glucosamine and uronic acid residues, has been used clinically as an anticoagulant for half a century. Despite a yearly use of over 50 million doses in the U.S. alone, heparin's exact chemical structure remains unclear. The negative ion fast atom bombardment mass spectrometry (FAB-MS) analysis is presented for a series of enzymatically prepared, homogeneous, structurally characterized, highly sulfated, heparin-derived oligosaccharides using triethanolamine as the FAB matrix. In addition to the clear presence of monoanionic sodiated molecular ions, structurally significant (sequence) fragment ions are observed and characterized with respect to the known structure for five of the heparin-derived oligosaccharides. The structure of a sixth oligosaccharide is predicted by using negative ion FAB-MS and subsequently confirmed by chemical, enzymatic, and NMR spectroscopic methods.

Comparison of electron ionization and fast atom bombardment-mass spectrometry for the determination of nickel, vanadyl and free-base porphyrins

Fast Atom Bombardment-Mass Spectrometry (FAB-MS) and Electron Ionization-Mass Spectrometry (EI-MS) at 12 and 70 eV, were used to obtain mass spectra of mesoporphyrin IX dimethylester (DME), tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), and the metalloporphyrins, Ni(DME), Ni(TPP), Ni(OEP), VO(TPP), VO(OEP), as well as a VO(II) porphyrin concentrate obtained from the New Albany oil shale bitumen (Mississippian-Devonian). A mixture of dithiothreitol/dithioerythritol (“Magic Bullet”) was used as the FAB matrix. Greater fragmentation of free-base and metalloporphyrins was observed in FAB mass spectra compared to the EI mass spectra. Adduct ions formed by addition of sulfur and a matrix molecule to the porphyrins were observed. In FAB spectra of the VO(II) complexes, loss of oxygen was noted. The FAB mass spectra of mixtures of VO(II) geoporphyrins are much more complex than corresponding EI mass spectra because of the greater fragmentation and the multiplicity of ions (M +, M + H, M + 2H, etc.) observed in the FAB mode. Using the matrices investigated, FAB is less suitable for EI for the mass spectrometric analysis of the geoporphyrins.

Continuous flow fast atom bombardment liquid chromatography/mass spectrometry: studies involving conventional bore liquid chromatography with simultaneous ultraviolet detection.

A conventional bore liquid chromatograph has been interfaced to quadrupole and magnetic sector mass spectrometers configured for fast atom bombardment ionization via a continuous flow FAB probe. It is shown that post-column addition of FAB matrix and in-line ultraviolet detection facilities do not significantly compromise chromatographic integrity and that high quality mass spectra are obtainable from such FAB LC/MS studies.

Trace level measurement of enkephalin peptides at the attomole/femtomole level by FAB-MS. Optimization of FAB matrix conditions.

Trace level measurement of enkephalin peptides at the attomole/femtomole level by FAB-MS. Optimization of FAB matrix conditions.

Oligosaccharide Structural Studies by On-Line HPLC-MS using Fast Atom Bombardment Ionization

Abstract A moving polyimide belt was used as an HPLC-MS interface for the purification and structural studies of oligosaccharides. The samples, desorbed by FAB in the absence of added liquid matrix, exhibited the following characteristics: a) good signal to noise ratio at low mass; b) a variation in the degree of fragmentation and relative sensitivity with changes in belt speed; c) a diminished sensitivity to signal suppression by contaminants when contrasted to FAB matrix; and d) fragment ions which can provide useful structural information. The moving belt HPLC-MS interface was tested with a series of known standards and a sample of high mannose oligosaccharides isolated from animal urines.