Evidence for linkage position determination in known feruloylated mono- and disaccharides using electrospray ion trap mass spectrometry

Various feruloylated arabinose- and galactose-containing mono- and disaccharides with known linkage configurations (2-O-(trans-feruloyl)-L-arabinopyranose, 5-O-(trans-feruloyl)-L-arabinofuranose, O-[2-O-(trans-feruloyl)-alpha-L-arabinofuranosyl]-(1-->5)-L-arabinofuranose, and O-[6-O-(trans-feruloyl)-beta-D-galactopyranosyl]-(1-->4)-D-galactopyranose) were analyzed by electrospray ionization mass spectrometry using an ion trap or a quadrupole time-of-flight (Q-TOF) mass analyzer. Collision-induced dissociation (CID) experiments using the two mass analyzers generated similar tandem mass spectrometric (MS/MS) fragmentation patterns. However, the ester-bond cleavage ions were more abundant using the Q-TOF mass analyzer. Compared with the positive ion mode, the negative ion mode produces simpler and more useful CID product-ion patterns. For arabinose-containing feruloylated compounds, results obtained with both analyzers show that it is possible to assign the location of the feruloyl group to the O-2 or O-5 of arabinosyl residues. In the characterization of the 2-O-feruloyl and 5-O-feruloyl linkages, the relative abundance of the cross-ring fragment ions at m/z 265 (-60 u or -62 u after 18O-labelling) and at m/z 217 (-108 u or -110 u after 18O-labelling) play a relevant role. For galactose-containing feruloylated compounds, losses of 60, 90 and 120 Da observed in MS3 experiment correspond to the production of 0,2A1, 0,3A1 and (0,2A1-60 Da) cross-ring cleavage ions, respectively, fixing the location of feruloyl group at the O-6 of the galactose residue.     

High-pressure ion trap mass spectrometry

The effects of buffer gas pressure on ion trap stability, mass resolution/calibration, and choice of mass scanning are described. Pressure effects were treated phenomenologically by adding a drag term to the ion equations of motion. The resulting collisional damping enlarges the mass-dependent stability region but reduces the region in which mass-selective resonance ejection can be performed. The pressure effects can be reduced by increasing the frequency of the alternating quadrupole field.     

A combined linear ion trap for mass spectrometry

We propose a novel ion cyclotron resonance ion trap capable of confining ions even at high pressure. The trap consists of three capacitively coupled axial sections, each composed of four circular cross-section rods parallel to the magnetic field axis. Ion confinement along the magnetic field direction is provided by applying the same static voltage to each set of “endcap” rods. As for a two-dimensional quadrupole mass filter, a sufficiently high rf frequency (several MHz) leads to an “effective” electrostatic “pseudopotential” well with a minimum on the trap central axis. Ions are confined radially by the combination of an applied axial static magnetic field and a radially inward-directed electric field resulting from differential rf voltages applied to each set of four rods. Ion confinement properties are revealed from a Paul traplike “stability diagram,” whereas ion trajectories are analyzed in terms of Penning-type ion cyclotron rotation, magnetron rotation, and axial oscillation motional modes. Ion cyclotron frequency increases with the strength of the rf trapping field. Ion magnetron motion becomes stable if the rf voltage is high enough. Therefore, ion trajectories can be stable even in the presence of ion-neutral collisions. Adding an ac potential to a Penning trap should dramatically increase the upper mass detection limit.     

Quadrupole ion trap mass spectrometry of fullerenes

The fullerenes C₆₀ and C₇₀ can be ionized by desorption from a liquid matrix upon bombardment by Cs⁺ ions of 7 keV kinetic energy. The resulting radical cations, when activated in the ion trap by collisions with Xe target, in the presence of helium, undergo extensive dissociation by loss of multiple C₂ units. Large internal energies are deposited into these molecular ions and the dissociation efficiency is in excess of 60%.     

离子阱颗粒质谱研究进展

随着质谱技术的不断发展,对超高质量颗粒物质的分析已经成为质谱领域研究的一个重要方向.离子阱颗粒质谱(particle ion trap mass spectrometry)作为用于完整颗粒质量分析的有利工具,拓展了质谱技术在巨大颗粒物质量分析中的应用范围.本文对离子阱颗粒质谱仪器的研究进展及其在各个领域的应用进行了综述,并展望了离子阱颗粒质谱未来的发展趋势.     

Recent developments in analytical ion trap mass spectrometry

The current status of quadrupole ion trap mass spectrometry is reviewed, with particular emphasis on liquid chromatographic coupling, membrane inlet introduction, laser desorption/ionisation and selective chemical ionisation. The flexibility, high sensitivity and multi-stage tandem mass spectrometric capability of the quadrupole ion trap are all illustrated.     

Fragmentations of isomeric sulfated monosaccharides using electrospray ion trap mass spectrometry

Electrospray ionization combined with ion trap mass spectrometry (ESI-ITMS) is a powerful tool for structural analysis of complex carbohydrates. Although its application to sulfated glycans has been limited so far, it should provide critical information, such as sulfate positions, on their structures. In this work, MS(n) spectra of nine monosulfated monosaccharides, consisting of five hexoses and four N-acetylhexosamines, were measured in negative ion mode to find basic fragmentation rules for sulfated sugars. Two pairs of positional isomers with respect to sulfation, i.e., Gal4S and Gal6S, and GalNAc4S and GalNAc6S, showed characteristic fragmentation patterns in MS(3), and could be discriminated from one another by the appearance of particular diagnostic fragment ions that characterize individual isomers. It was also demonstrated that, even if a mixture of these positional isomers was analyzed, the proportion of each species could be estimated through analysis of the abundance ratios of the diagnostic ions. However, 3-O-sulfated saccharides (Glc3S and GlcNAc3S) gave a single abundant diagnostic ion in MS(2) corresponding to the hydrogensulfate ion, [OSO(3)H](-), and this characteristic clearly differentiated them from their positional isomers. In contrast, 6-O-sulfated diastereomers consisting of two groups, Glc6S, Man6S, Gal6S, and GlcNAc6S, GalNAc6S, could not be discriminated by the types of fragment ions; however, the abundance ratios of particular fragment ions differed significantly between Glc(NAc)6S and Gal(NAc)6S. Since ESI-ITMS yielded large quantities of useful information on structures of monosulfated hexoses and N-acetylhexosamines in an extremely simple and reproducible manner, establishment of a comprehensive strategy based on ESI-ITMS(n) appears to be a promising technique for structural elucidation of sulfated complex carbohydrates.     

Characterisation of selected hypnotic drugs and their metabolites using electrospray ionisation with ion trap mass spectrometry and with quadrupole time-of-flight mass spectrometry and their determination by liquid chromatography-electrospray ionisation-ion trap mass spectrometry

The electrospray ionisation-ion trap mass spectrometry (ESI-MSⁿ) of selected hypnotic drugs, i.e. zopiclone, zolpidem, flunitrazepam and their metabolites have been investigated. Sequential product ion fragmentation experiments (MSⁿ) have been performed in order to elucidate the degradation pathways for the [M+H]⁺ ions and their predominant fragment ions. These MSⁿ experiments show certain characteristic fragmentations in that functional groups are generally cleaved from the ring systems as neutral molecules such as H₂O, CO, CO₂, NO₂, amines and HF. When an aromatic entity is present in a drug molecule together with a nitrogen-containing saturated ring structure as with zopiclone and its N-desmethyl metabolite fragmentation initially occurs at the latter ring with the former being resistant to fragmentation. The structures of fragment ions proposed for ESI-MSⁿ can be supported by electrospray ionisation-quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS).These molecules can be identified and determined in mixtures at low ng/ml concentrations by the application of liquid chromatography (LC)-ESI-MSⁿ which can be used for their analysis in saliva samples.This paper includes a tabulation of mass losses/signals at low m/z values for these hypnotic drugs and many others in recent publications which will be of value in the characterisation of drug metabolites of unknown structure and also natural product pharmaceuticals isolated from plants, etc.     

Analysis of vitamin E derivatives in serum using coordinated ion spray mass spectrometry

A method for the extraction and analysis of tocopherols from serum using coordinated ion spray (CIS) mass spectrometry was developed and tested. The tocopherols were extracted from serum and analyzed by direct infusion into the mass spectrometer, bypassing the need for a liquid chromatography step. CIS is a method for improving the ionization efficiency of non-polar compounds by adding metal ions to the electrospray solvent. The non-polar analytes appear as metal adducts in the resulting mass spectrum. Silver was used as the metal ion for the CIS, causing analyte masses to be increased by 107 and 109 Da from the two main silver isotopes. Vitamin E succinate was added to the samples before extraction and was used as an internal standard to compensate for any variations in the extraction efficiency or mass spectrometric response. alpha-Tocopherol and an ether-linked analogue known as alpha-TEA were analyzed in concentrations from 1.25-40 microg/mL (1.9-60 pg consumed). The response curve was constructed by comparing the response of the analytes to the internal standard and gave linear results with r2 values greater than 0.98. This new method was shown to be sensitive, reproducible, fast and required very small amounts of analyte.     

Multi-residue determination of 41 insecticides in garlic by gas chromatography and ion trap mass spectrometry using the selective ion storage technique

A method is described for determining 41 insecticide residues in garlic (Allium sativum L.), including organophosphorus, organochlorine, carbamate, and synthetic pyrethroid insecticides. These insecticides were extracted from samples with acetone and dichloromethane, and co-extractives removed using a charcoal/Celite/alumina column. Analysis was performed by gas chromatography with ion trap mass spectrometry in selective ion storage (SIS) mode. Retention times and specific ions (m/z values) were used to confirm insecticides. Recoveries for most insecticides (blank samples spiked at 0.05, 0.2 and 1 microg mL(-1) levels) ranged from 70% to 110%, the coefficient of variation (CV) of the method was <20% for every case, and the limit of detection (LOD), defined in terms of 3 times baseline noise, varied between 0.01 and 0.16 mg kg(-1), depending on the compound.     

Enhanced mass resolution tandem mass spectrometry method for 2,3,7,8-tetrachlorodibenzo-p-dioxin detection with ion trap mass spectrometry using high damping gas pressure

Damping gas flow was optimized for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) determination using ion trap mass spectrometer. A tandem mass spectrometry (MS-MS) method with better than unit-mass resolution (mass width, 0.3 u) was developed at a damping gas flow of 1.5 ml/min and a collision-induced dissociation (CID) voltage of 3.30 V. The relative standard deviation (R.S.D.) at the enhanced resolution was 2.9% in 24 h of consecutive injections. The detection limit was significantly improved because the efficiency of both precursor ion trapping and fragmentation increased with the damping gas flow. Product ion yield was 4.5 times higher and limit of detection was 3.2 times lower than at the default flow (0.3 ml/min and 1.65 V).     

Low pressure chemical ionization in ion trap mass spectrometry

This article presents the specificities of low pressure chemical ionization in ion trap mass spectrometry. One main feature is the ability to perform chemical ionization with liquid reagents as readily as with "conventional" gases (methane, isobutane and ammonia). The reactivities and analytical applications of gas and liquid reagents are summarized from literature data and are compared when possible.     

The identification of in vitro metabolites of bupropion using ion trap mass spectrometry

We have identified in vitro metabolites of bupropion (Wellbutrin®) from incubations with human liver S9 fraction and human liver microsomes based on molecular weight information from full scan experiments using a liquid chromatograph coupled to a quadrupole ion trap mass spectrometer capable of multi-stage operation (LC/MSⁿ). Preliminary experiments have shown that this instrument provides comparable sensitivity to conventional LC-coupled triple quadrupole instruments for metabolic studies, while allowing detailed structural studies using MS_n experiments and routine on-line coupling with high performance liquid chromatography via an external atmospheric pressure chemical ionization (APCI) source. The LC/MS analysis of human S9 showed the presence of three isomeric monohydroxylated metabolites of bupropion. These were further characterized in a series of MS/MS experiments which gave characteristic spectra for the three isomers. A minor dihydroxylated species was also identified in the human S9 sample and further characterized in a series of MS_n experiments. Detailed structural information was generated by the use of on-line LC/MS_n type experiments. We have followed the fragmentation pathways of several molecular ion species in a series of sequential LC/MS_n experiments, extending as far as MS⁶ with scan cycle times of less than 1.5 s. Such experiments have provided insights into the structure of specific fragment ions. Additional metabolic products were identified in the rat liver microsomes incubation sample.     

Fragmentation studies on the antibiotic avilamycin A using ion trap mass spectrometry

A comprehensive study on the fragmentation pattern of the antimicrobial growth promoter avilamycin A was conducted in a quadrupole ion trap mass spectrometer equipped with an electrospray ionization (ESI) source. Performing multiple-stage experiments on the deprotonated molecule (m/z 1401) and its principal product ions showed that a sequential shortening of the oligosaccharide backbone took place, which can be attributed to the localization of the negative charge in the terminal dichloroisoeverninic acid. Under (+)-ESI conditions, avilamycin A readily formed an intense sodium-cationized molecule, [M + Na](+) (m/z 1425). Structural elucidation of the second-, third- and fourth-generation fragment ions revealed that all of the structures shared a common molecular portion comprising a central monosaccharide. This observation allowed us to assign confidently the complexation site of the alkali metal cation. In addition to the monosodiated molecule, the full-scan mass spectral acquisition also yielded a less abundant disodiated molecule, [M - H + 2Na](+) (m/z 1447). Multiple-stage experiments on this ion indicated that the second sodium ion compensates for the negative charge located at either of two positions within the molecule. While deprotonation of the phenolic hydroxyl group in the dichloroisoeverninic acid moiety was suggested to be driven by charge stabilization in the aromatic ring (in analogy with the deprotonated molecule in the (-)-ESI mode), the deprotonation at an alpha-carbon of an ester side-chain substituent in the oligosaccharide part was believed to provide a stable chelation-like coordination site for the cation.     

The distinction of underivatized monosaccharides using electrospray ionization ion trap mass spectrometry

A convenient method for distinguishing underivatized isomeric monosaccharides has been established using electrospray ionization ion trap mass spectrometry (ESI-ITMS). Mass spectra of hexoses (glucose, galactose, and mannose), N-acetylhexosamines (N-acetylglucosamine, N-acetylgalactosamine, and N-acetylmannosamine) and hexosamines (glucosamine, galactosamine, and mannosamine) dissolved in solvent containing 1 mM ammonium acetate were obtained in the positive ion mode. Glucose was distinguished from galactose and mannose in the MS(2) spectrum of the [M+NH(4)](+) ion at m/z 198. The MS(3) spectra generated from [M+NH(4)-H(2)O-NH(3)](+) at m/z 163 showed that galactose and mannose could be distinguished by the ratio of peak intensities at m/z 145 and 127, while the three N-acetylhexosamine and hexosamine stereochemical isomers could be identified by the relative abundance ratios of product ions observed in MS(3) spectra. The investigation of MS and MS(2) spectra from complexes of these monosaccharides with Na(+) and Pb(2+) failed to distinguish these monosaccharide isomers. Therefore, multiple stage mass analysis by ESI-ITMS using either [M+NH(4)](+) or [M+H](+) was useful to distinguish between the isomers of monosaccharides.     

Oligonucleotide sequencing using guanine-specific methylation and electrospray ionization ion trap mass spectrometry

This paper describes a novel method to map guanine bases in short oligonucleotides using a simple chemical modification reaction and subsequent analysis by electrospray ionization ion trap mass spectrometry (ITMS). In situ guanine-specific methylation followed by gas-phase fragmentation permits the determination of the positions of all guanine residues. Collision-induced dissociation (CID) of the monomethylated oligonucleotide strand promotes rapid depurination and further collision (MS3) of the apurinic oligonucleotide leads to preferential cleavage of the backbone at the site of depurination. The mass of the resulting complementary product ions verifies the position of each guanine base in the sequence. The utility of this methodology is demonstrated for oligonucleotide sequences up to 10 bases in length. In addition, this technique successfully illustrates the use of selective fragmentation for sequencing oligonucleotides by ITMS.     

Characterization of VX on concrete using ion trap secondary ionization mass spectrometry

The nerve agent VX (O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) was analyzed on the surface of concrete samples using an ion trap secondary ion mass spectrometer (IT-SIMS). It was found that VX could be detected down to an absolute quantity of 5 ng on a concrete chip, or to a surface coverage of 0.0004 monolayers on crushed concrete. To achieve these levels of detection, the m/z 268-->128 ion fragmentation was measured using MS2, where m/z 268 corresponds to [VX + H]+, and 128 corresponds to a diisopropylvinylammonium isomer, that is formed by the elimination of the phosphonothiolate moiety. Detection at these levels was accomplished by analyzing samples that had been recently exposed to VX, i.e., within an hour. When the VX-exposed concrete samples were aged, the SIMS signature for intact VX had disappeared, which signaled the degradation of the compound on the concrete surface. The VX signature was replaced by ions which are interpreted in terms of VX degradation products, which appear to be somewhat long lived on the concrete surface. These compounds include ethylmethylphosphonic acid (EMPA), diisopropyl taurine (DIPT), diisopropylaminoethanethiol (DESH), bis(diisopropylaminoethane) disulfide [(DES)2], and a particularly tenacious compound that may correspond to diisopropylvinylamine (DIVA), or an isomer thereof. It was found that the thiolamine-derived degradation products DIPT, DESH, and (DES)2 were removed with isopropyl alcohol extraction. However, the DIVA-related degradation product was observed to strongly adhere to the concrete surface for longer than one week. Although quantitation was not possible in this set of experiments, the results clearly show the rapid degradation of VX on concrete, as well as the surface sensitivity of the IT-SIMS for intact VX and its adsorptive degradation products.     

Laser desorption lamp ionization source for ion trap mass spectrometry

A two‐step laser desorption lamp ionization source coupled to an ion trap mass spectrometer (LDLI‐ITMS) has been constructed and characterized. The pulsed infrared (IR) output of an Nd:YAG laser (1064 nm) is directed to a target inside a chamber evacuated to ~15 Pa causing desorption of molecules from the target's surface. The desorbed molecules are ionized by a vacuum ultraviolet (VUV) lamp (filled with xenon, major wavelength at 148 nm). The resulting ions are stored and detected in a three‐dimensional quadrupole ion trap modified from a Finnigan Mat LCQ mass spectrometer operated at a pressure of ≥ 0.004 Pa. The limit of detection for desorbed coronene molecules is 1.5 pmol, which is about two orders of magnitude more sensitive than laser desorption laser ionization mass spectrometry using a fluorine excimer laser (157 nm) as the ionization source. The mass spectrum of four standard aromatic compounds (pyrene, coronene, rubrene and 1,4,8,11,15,18,22,25‐octabutoxy‐29H,31H‐phthalocyanine (OPC)) shows that parent ions dominate. By increasing the infrared laser power, this instrument is capable of detecting inorganic compounds. Copyright © 2015 John Wiley & Sons, Ltd.     

Boundary-effect activated dissociation in ion trap tandem mass spectrometry

The potential of boundary-effect activated dissociation (BAD) in ion trap tandem mass spectrometry (MS/MS) is discussed. Several classes of compounds were investigated and the BAD product ion tandem mass spectra were compared with those from collisionally activated dissociation (CAD) where an auxilliary r.f. ‘tickle’ voltage is used. The energy deposition in BAD MS/MS is generally lower than that for optimized CAD, but the experiments are easier to perform. An example of the BAD MS/MS of C₁₀ alkylbenzenes and benzothiophene in diesel fuel using gas chromatographic introduction and predicted r.f. and d.c. voltages is presented.