Ammonia desorption chemical ionization mass spectrometry of phospholipids

Ammonia desorption chemical ionization mass spectra (NH₃-DCIMS) of phosphatidyl-sulfocholines, a mixture of a homologous series of phosphatidylsulfocholines (PSC) and a mixture of a PSC phosphatidylcholine (PC), were measured by a flash heating method involving introduction of 1 μg of the samples on a tungsten wire, quickly heated, into the ion source of a Finnigan 4000/INCOS quadrupole instrument. It was possible to observe mass spectra during several seconds.The first spectra recorded of the PSCs gave essentially only the quasi-molecular [M + 18]⁺ peaks and the ‘A’ (see text) peaks. Spectra of a mixture of three homologous PSCs clearly showed three pairs of the above peaks. In contrast spectra of the PCs gave principally the [M + 1]⁺ and the ‘A’ peaks after 2s so that one can distinguish the diagnostic peaks in a mixture of a PC and a PSC.These results show that ammonia desorption chemical ionization by fast heating is a suitable technique for the charaterization of some head groups of phospholipids as well as a promising method for the analysis of phospholipid mixtures.     

Ammonia desorption chemical ionization mass spectrometry of phosphatidylsulfocholine-phosphatidylcholine mixtures

Unhydrogenated or hydrogenated phosphatidylsulfocholine (2 μg) of the non-photosynthetic diatom Nitzschia alba was analyzed by ammonia desorption chemical ionization mass spectrometry (NH₃-DCIMS) using a flash heating method. Each molecular species was recognized by its quasi-molecular [M + 18]⁺ ion peak and by a substitution ion which corresponds to the replacement of -

(CH₃)₂ by -

H₃. With unhydrogenated or hydrogenated mixtures (3 μg) of Nitzschia alba phosphatidylsulfocholine and egg yolk phosphatidylcholine, in weight proportions 1:1, 1:2 and 1:5, respectively, the phosphatidylsulfocholine diagnostic [M + 18]⁺ ions appeared ahead of the phosphatidylcholine diagnostic [M + 1]⁺ ions, thus allowing analysis of phosphatidylsulfocholine separately from phosphatidylcholine. These results show that NH₃-DCIMS with fast heating is a suitable technique to study complex phosphatidylsulfocholine-phosphatidylcholine mixtures. This technique should be directly applicable to the detection of phosphatidylsulfocholine in natural phosphatidylsulfocholine-phosphatidylcholine mixtures as well as to the identification of their main molecular species.     

Matrix-assisted ultraviolet laser desorption/ionization time-of-flight (UV-MALDI-TOF) mass spectra of N-acylated and N,O-acylated glycosylamines

Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF-MS) has shown to be a very useful technique for the study of the non-volatile and thermally non-stable N-acylated glycopyranosyl- and glycofuranosyl-amines. Of the several matrices tested, 2,5-dihydroxybenzoic acid (DHB) was the most effective giving good spectra in the positive-ion mode. In the linear and reflectron modes, the [M+Na](+) ions appeared with high intensity. Their fragmentation patterns were investigated by post-source decay (PSD) UV-MALDI-TOF-MS showing mainly cross-ring cleavages. In addition, N,O-acylated glycopyranosyl- and glycofuranosyl-amines were also analyzed by this technique. PSD UV-MALDI-TOF-MS gave significant signals for several primary fragment ions, which were proposed but not detected, or observed with very low abundance, in electron ionization mass spectrometry (EI-MS) experiments.     

Spatially resolved analysis of small molecules by matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI)

? Matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) of tissues provides the means to analyse the spatial distributions of small molecules and proteins within tissues. This imaging technique is commonplace in medicinal and pharmaceutical research, but its application in plant science is very recent. Broader introduction requires specific adaptations for plant tissues. Sample preparation is of paramount importance in order to obtain high-quality spectra providing sufficient spatial resolution for compounds. Optimization is required for sectioning, choice of matrix and means of matrix deposition. ? Here, we present our current protocols for the detection of small molecules in cryodissected immature barley (Hordeum vulgare) grains and tobacco (Nicotiana tabacum) roots. ? Examples of MALDI-MSI measurements are provided, and the level of reproducibility across biological replicates is addressed. Furthermore, our approaches for the validation of distribution patterns and for the identification of molecules are described. ? Finally, we discuss how MALDI-MSI can contribute to applied plant research.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based amino acid analysis

Amino acid analysis has been an integral part of analytical biochemistry for more than 50 years. However, its experimental design, which includes derivatization of amino acids followed by some kind of chromatographic separation, has not changed over the years. We have developed a matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)-based method for the quantitative analysis of amino acids. This method does not require any amino acid modification, derivatization, or chromatographic separation. The data acquisition time is decreased to several seconds for a single sample. No significant ion suppression effects were observed with the developed sample deposition technique, and the method was found to be reproducible. Linear responses between the amino acid concentration and the peak intensities ratio of corresponding amino acid to internal standard were observed for all amino acids analyzed in the range of concentrations from 20 to 300 microM, and correlation coefficients were between 0.983 (for arginine) and 0.999 (for phenylalanine). Limits of quantitation were between 0.03 microM (for arginine) and 3.7 microM (for histidine and homocysteine). This method was applicable to the mixtures of free amino acids as well as to HCl hydrolysates of proteins. Furthermore, we have shown that this method can be applied to other biologically important low-molecular weight compounds such as glucose.     

Surface-assisted laser desorption/ionization mass spectrometry

Laser desorption/ionization mass spectrometry (MS) is rapidly growing in popularity as an analytical characterization method in several fields. The technique shot to prominence using matrix-assisted desorption/ionization for large biomolecules (>700 Da), such as proteins, peptides and nucleic acids. However, because the matrix, which consists of small organic molecules, is also ionized, the technique is of limited use in the low-molecular-mass range (<700 Da). Recent advances in surface science have facilitated the development of matrix-free laser desorption/ionization MS approaches, which are referred to here as surface-assisted laser desorption/ionization (SALDI) MS. In contrast to traditional matrix-assisted techniques, the materials used for SALDI-MS are not ionized, which expands the usefulness of this technique to small-molecule analyses. This review discusses the current status of SALDI-MS as a standard analytical technique, with an emphasis on potential applications in proteomics.     

Surface-assisted laser desorption/ionization mass spectrometry

Laser desorption/ionization mass spectrometry (MS) is rapidly growing in popularity as an analytical characterization method in several fields. The technique shot to prominence using matrix-assisted desorption/ionization for large biomolecules (>700 Da), such as proteins, peptides and nucleic acids. However, because the matrix, which consists of small organic molecules, is also ionized, the technique is of limited use in the low-molecular-mass range (<700 Da). Recent advances in surface science have facilitated the development of matrix-free laser desorption/ionization MS approaches, which are referred to here as surface-assisted laser desorption/ionization (SALDI) MS. In contrast to traditional matrix-assisted techniques, the materials used for SALDI-MS are not ionized, which expands the usefulness of this technique to small-molecule analyses. This review discusses the current status of SALDI-MS as a standard analytical technique, with an emphasis on potential applications in proteomics.     

Ambient desorption ionization mass spectrometry (DART, DESI) and its bioanalytical applications

In recent years, ambient desorption ionization techniques for mass spectrometry were introduced. Among them, the most established techniques are Direct Analysis in Real Time (DART) and Desorption Electrospray Ionization (DESI). Therefore, the current review focuses on the bioanalytical applications of ambient desorption ionization techniques by the example of DART and DESI mass spectrometry. The potential and also limitations of both ambient mass spectrometry (MS) techniques in such areas, as identification and quantitation of small molecules, coupling DART-MS and DESI-MS with planar chromatography, protein/peptide analysis, as well as molecular imaging applications, are discussed.     

Betaines of alfalfa : characterization by fast atom bombardment and desorption chemical ionization mass spectrometry

Leaf tissue of alfalfa (Medicago sativa L.) was found to contain prolinebetaine, pipecolatebetaine, hydroxyprolinebetaine, and glycinebetaine. As n-butyl esters, these chemical species exhibit molecular cations at mass/charge ratio (m/z) 200, 214, 216, and 174, respectively, when analyzed by fast atom bombardment mass spectrometry. The underivatized betaines exhibit protonated molecular ions at m/z 144, 158, 160, and 118, respectively, when analyzed by desorption chemical ionization mass spectrometry. Extensive (>45-fold) genotypic variation for hydroxyprolinebetaine level was identified in alfalfa. Because a significant inverse correlation between prolinebetaine and hydroxyprolinebetaine levels was observed among 15 alfalfa genotypes evaluated, it is possible that these compounds may be derived from a common intermediate. Birdsfoot trefoil (Lotus corniculatus L.) contained prolinebetaine, but only traces of glycinebetaine, pipecolatebetaine, and hydroxyprolinebetaine. Red clover (Trifolium pratense L.) lacked prolinebetaine, pipecolatebetaine, and hydroxyprolinebetaine, but contained appreciable levels of both glycinebetaine and trigonelline. Trigonelline was not detectable in the leaf tissue of any alfalfa genotype or cultivar evaluated.     

Targeted metabolomic analysis of Escherichia coli by desorption electrospray ionization and extractive electrospray ionization mass spectrometry

Desorption electrospray ionization (DESI) was utilized to monitor the presence of targeted central carbon metabolites within bacterial cell extracts and the quench supernatant of Escherichia coli. The targeted metabolites were identified through tandem mass spectrometry (MS/MS) product ion scans using collision-induced dissociation in the negative ion mode. Picogram detection limits were achieved for a majority of the metabolites during MS/MS analysis of standard metabolite solutions. In a [U-(13)C]glucose pulse experiment, where uniformly labeled glucose was fed to E. coli, the corresponding fragment ions from labeled metabolites in extracts were generally observed. There was evidence of matrix effects including moderate suppression by other metabolites within the spectra of the labeled and unlabeled extracts. To improve the specificity and sensitivity of detection, optimized in situ ambient chemical reactions using DESI and extractive electrospray ionization (EESI) were carried out for targeted compounds. This study provides the first indication of the potential to perform in situ targeted metabolomics of a bacterial sample via ambient ionization mass spectrometry.     

Sequence analysis of chitooligosaccharides by matrix-assisted laser desorption ionization postsource decay mass spectrometry

Chitin/chitosan oligosaccharides composed of 2-acetamido-2-deoxy-D-glucopyranose (GlcNAc) and/or 2-amino-2-deoxy-D-glucopyranose (GlcN) were prepared by chemical degradation of chitin or chitosan and separated by gel permeation chromatography. Oligosaccharides obtained after enzymatic hydrolysis of chitosan [F(A) 0.19] with a fungal chitinase were derivatized by reductive amination with 2-aminoacridone and sequenced by matrix-assisted laser desorption ionization time-of-flight postsource decay (PSD) mass spectrometry (MS). The sequence of a trimer, D1A2, was established as D-A-A. The composition of a hexamer D3A3 was ca. 65% D-A-D-D-A-A and 35% D-D-A-D-A-A. The PSD MS of a nonamer D5A4-amac revealed four isobaric species D-X-Y-D-X-Y-D-A-A, where A is GlcNAc, D is GlcN, and X and Y (X not equal Y) are mutually either D or A. This structure motif was also observed in a dodecamer D7A5 which was composed of eight isobaric sequences of the general formula (D-X-Y)(3)-D-A-A.     

Matrix-assisted laser desorption ionization time-of-flight mass spectrometric analysis of glycosphingolipids including gangliosides.

Long chain base compositions of gangliosides containing mainly stearic acid could be determined without any chemical modification by matrix-assisted laser desorption ionization time-of-flight mass spectrometry with delayed ion extraction (DE MALDI-TOF MS). The analytical results for the long chain base compositions of various samples of GM1 from the brain tissues of patients with different diseases at different ages confirmed that the proportion of d20:1 (icosasphingosine) and d20 (icosa-sphinganine) of the total sphingosine bases increased quickly until adolescent or adult age and then remained constant slightly exceeding 50%; this value was evidently higher than the proportion of d20:1 and d20 of GM1 in various adult mammalian brains. A long chain base composition of GM1 from the brain tissue of a patient with infantile type of GM1-gangliosidosis at 4y2m was abnormal and so was in two sibling patients with Spielmeyer-Vogt type of juvenile amaurotic idiocy at 19y and 21y in spite of that in the latter there was no accumulation of GM1 in the brain tissue. On the other hand, a patient with adult type of GM1 gangliosidosis at 66y showed a local accumulation of GM1 in the putamen and caudate nucleus, but its long chain base composition was found to be normal. It was of interest that the white matter of Eker rat with hereditary renal carcinoma contained a large amount of plasmalocerebroside as compared with the amount of cerebroside and sphingomyelin. The individual molecular species of plasmalocerebroside were identified by DE MALDI-TOF MS.     

Automatic annotation of matrix-assisted laser desorption/ionization N-glycan spectra

Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is the pre-eminent technique for mass mapping of glycans. In order to make this technique practical for high-throughput screening, reliable automatic methods of annotating peaks must be devised. We describe an algorithm called Cartoonist that labels peaks in MALDI spectra of permethylated N-glycans with cartoons which represent the most plausible glycans consistent with the peak masses and the types of glycans being analyzed. There are three main parts to Cartoonist. (i) It selects annotations from a library of biosynthetically plausible cartoons. The library we currently use has about 2800 cartoons, but was constructed using only about 300 archetype cartoons entered by hand. (ii) It determines the precision and calibration of the machine used to generate the spectrum. It does this automatically based on the spectrum itself. (iii) It assigns a confidence score to each annotation. In particular, rather than making a binary yes/no decision when annotating a peak, it makes all plausible annotations and associates them with scores indicating the probability that they are correct.     

Laser desorption Fourier transform mass spectra of malto-oligosaccharides

Laser desorption mass spectra of malto-oligomers, including starch, have been obtained using Fourier transform mass spectrometry. Fragmentations of these oligomers have been examined after doping with metal salts to obtain cation-attachment ions. Doping starch with NaCl, KBr and Ag2O results in analogous cation-attachment oligosaccharide fragment ions for all three metal ions. A distinct and unusual fragmentation pattern is observed for the larger oligomers.     

Characterization of propionic acid bacteria using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry

It was shown that matrix-assisted laser desorption/ionization (MALDI) mass spectrometry could be used for the diagnostic characterization of propionic acid bacteria (PABs). The spectra of proteins (whole PAB cells) with a molecular mass of 3000 to 11 000 were obtained and analyzed using three matrices: sinapinic (SA), 2,5-dihydroxibenzoic (DHB), and α-cyano-4-hydroxycinnamic acid (HCCA). The MALDI spectra of PAB revealed the protein peaks characteristic of (1) the genus Propionibacterium (3496, 5386, 5605, 10 470), (2) the groups of species sharing the common composition of their cell walls and fatty acids, and (3) a species (four species were investigated). Exemplified by the P. shermanii strains (the collection and mutant ones) producing and not producing vitamin B₁₂, the possibility of using MALDI profiles for strain differentiation was confirmed. The MALDI profiles of the propionic acid cocci of the genus Luteococcus differ substantially from the profiles of PAB strains of the genus Propionibacterium, which is an additional proof of the validity of whole-cell MALDI spectra for generic differentiation of bacteria. Our investigation shows that the bacterial groups determined using the MALDI profiles correlate with the phylogenetic 16S rRNA gene groups, thus demonstrating the high resolution of this method for the differentiation of intraspecific differences (subspecies, strains).     

Gas chromatography chemical ionization mass spectrometric analysis of diminazene in plasma

A quantitative and sensitive method was developed for the determination of diminazene in plasma. The assay involves the reduction of diminazene to 4-aminobenzamidine and 4-hydrazinobenzamidine. The latter is further reduced to give an additional mole of 4-aminobenzamidine which is extracted, acetylated and condensed with hexafluoroacetylacetone to form a volatile derivative that is subsequently analyzed by gas chromatography chemical ionization mass spectrometry. 4-Aminobenzylamidine was synthesized and used as an internal standard. The method is reproducible and its sensitivity limit using 1 ml of plasma is 0.1 microgram diminazene ml-1. This sensitivity limit is sufficient to detect plasma levels in cattle following therapeutic doses of the drug.