Electron ionization mass spectra and their reproducibility for trialkylsilylated derivatives of organic acids, sugars and alcohols

Mass spectra of trialkylsilyl derivatives of fatty acids, dicarboxylic acids, hydroxyacids, oxoacids, sugars, amino acids and alcohols were obtained. Amino acids were analyzed as tert-butyldimethylsilyl derivatives; all other model compounds were analyzed as trimethylsilyl derivatives. Reproducibility of the electron ionization (EI) mass spectra for the derivatives obtained was discussed. It was shown that, for many investigated derivatives, composition of the respective mass spectra depended greatly on ion source contamination. The trimethylsilylated alpha-tocopherol mass spectrum composition was most significantly influenced by ion source contamination. This compound can be used to test ion source contamination.     

Identification of Abnormal Urinary Organic Acids in Inherited Metabolic Diseases by Gas Chromatography-Mass Spectrometry

A gas chromatography/mass spectrometry (GC/MS) coupled system has been established for the confirmatory identification of abnormal urinary organic acids in inherited metabolic diseases. Samples of patient urines were extracted with an organic solvent and trimethylsilylated (TMS). A mass spectra of gas chromatographically separated TMS derivatives can be obtained using the GC/MS coupled system with a single analytical run. Those compounds with close methylene units (e.g., 4-hydroxyphenylacetaic acid and phenylpyruvic acid) in the gas chromatograph can be identified by their specific mass spectra. The results indicate that this GC/MS system is a powerful method for identifying abnormal urinary organic acids. These acids can be identified by comparison with authentic mass spectra established in our laboratories or with mass spectra files from other sources or they can be directly identified by analysis of the mass spectrum. By using this system, we were able to make positive identification of several inherited metabolic diseases found in Chinese patients, including phenylketonuria, propionic acidemia, and methylmalonic aciduria. This GC/MS system is a powerful tool for the diagnosis of inherited metabolic diseases.     

Mass spectrometry of humic substances of different origin including those from Antarctica A comparative study

Mass spectra of humic acids (HA) from different sampling sites (Antarctica, Brazil, Czech Republic, Mexico and USA) and origin (plant, soil, peat, and coal derived) were obtained by laser desorption/ionization time of flight mass spectrometry (LDI-TOF MS). Optimisation of the experimental conditions are given as the optimal value of the laser energy at 20–30% higher than the threshold. Under these conditions, reproducible mass spectra of HA samples were obtained. In the mass spectra the majority of the peaks are observed in the m/z region 100–1000 Da. Mass spectra fingerprints of HA were analyzed and, in spite of the differences in their origin, a number of common features and profiles (patterns of peaks) were observed in most of the samples. Very similar structural groups (patterns) of the peaks are present in the m/z range 717–918 Da for HA samples of quite different origins, countries or continents.

The tandem LDI-TOF MS and multivariate statistical tools allowed us to extract and elucidate underlying information contained in the mass spectra of the HA samples under study. Applying principal components and cluster analysis, it was, e.g. demonstrated that most of the Antarctica HA samples show distinguishable differences when compared with humic acids from other continents and of different origin.     

The application of glass micropacked columns in gas liquid solid chromatography to the GC-MS analysis of polar compounds

Summary High efficiency, glass micropacked columns are evaluated in terms of Van Deemter plots showing that the same number of theoretical plates is obtained for hydrocarbons and polar compounds, such as aliphatic primary amines, alcohols and carboxylic acids. A direct GC-MS coupling system is employed showing no loss in resolution in the ion source even for very polar compounds. It is shown that the high capacity of GLSC micropacked columns is very effective in obtaining interpretable mass spectra of minor compounds in complex organic mixtures. Mass spectra obtained with the direct coupling are compared with those obtained with a conventional packed column of the same efficiency making use of a Biemann separator.     

Retracted: Mass analysis by Ar‐GCIB‐dynamic SIMS for organic materials

Generally, dynamic secondary ion mass spectrometry (SIMS) has been mainly used as one of the most powerful tools for inorganic mass analysis. On the other hand, an Ar gas cluster ion beam (GCIB) has been developed and spread as a processing tool for surface flattening and also a projectile for time‐of‐flight (ToF) SIMS. In this study, we newly introduced an Ar‐GCIB as a primary ion source to a commercially available dynamic SIMS apparatus, and investigated mass spectra of amino acid films (such as Arginine and Glycine) and polymer films (Polyethylene: PE and Polypropylene: PP) as organic model samples. As a result, each characteristic fragment peak indicating the original molecular organic structure was observed in the acquired mass spectra. In addition, their own molecular ions of the amino acids were also clearly observed. Mass spectra of PE/PP blended‐polymer films acquired using Ar‐GCIB‐dynamic SIMS could be identified between pure PE and PE:PP = 1:3 mixture by applying principal component analysis (PCA).     

Structural analysis of underivatized sialic acids by combined high-performance liquid chromatography-mass spectrometry

Mass spectra of chemically ionized, positive ions of underivatized N,O-acylated sialic acids, 2-deoxy-2,3-didehydro-N-acetylneuraminic acid and sialyl-alpha(2-3)-lactose were obtained by combined high-performance liquid chromatography--mass spectrometry, using a direct liquid inlet system. The mass spectra of the different compounds for which fragmentation schemes are proposed enable the differentiation between sialic acids, although the localization of O-substituents is not possible. However, since the various sialic acids separated well on high-performance liquid chromatography, combined high-performance liquid chromatography-mass spectrometry allowed their unequivocal characterization.     

Gas chromatography-mass spectrometry of some biologically important short chain acid butyl esters.

Mass spectra of n-butyl esters of selected biologically important short chain fatty acids were obtained by using the technique of gas-liquid chromatography-mass spectrometry. The results indicate that simple cleavage is responsible for the primary fragmentation of the molecules. The mass spectral data are considered to be advantageous for the identification of unknown short chain acids.     

Cationization of organic molecules under pulsed laser induced ion generation

Mass spectra of various involatile organic compounds, obtained by surface analysis with a laser microprobe mass analyser are reported. Metal-cationized quasimolecular ions of adenine, adenosine, 5-adenylic acid and sucrose supported on metal foils were observed. Metal attachment can also be detected from mixtures of metal salts and the organic compounds. Silver-cationized sugar molecules and atomic silver ions solvated by (H₂O)_x and (NH₃)_x (x = 1,2) have been found. The mass spectra are compared with those obtained by secondary ion mass spectrometry and similar techniques, discussing the processes of ion generation involved.     

Separation and identification of organic and organometallic compounds by use of a liquid chromatography-particle beam-glow discharge mass spectrometry combination

Evaluation of the particle beam glow discharge mass spectrometry (PB-GDMS) system as a detector for liquid chromatography (LC) is described for the analysis of polycyclic aromatic hydrocarbons, steroids, selenoamino acids, and alkyllead compounds. A particle beam interface is used to introduce analyte species from the LC into a glow discharge source for subsequent vaporization and ionization. Mass spectra display classic EI fragmentation patterns for the organic compounds, as well as elemental and molecular information for the organometallic compounds. Chromatographic separations display good temporal correlation between UV and PB-GDMS detection modes. Detection limits for Pb in lead nitrate, triethyllead, and triphenyllead fall in the sub-ppb (ng) range.     

Coupling two-step laser desorption/ionization with aerosol time-of-flight mass spectrometry for the analysis of individual organic particles

Analysis of organic compounds in aerosol particles using real-time single particle techniques is difficult because of extensive fragmentation that occurs in the laser desorption/ionization step. In an effort to avoid such fragmentation processes, we coupled a “soft” two-step laser desorption/ionization technique (L2MS) with aerosol time-of-flight mass spectrometry (ATOFMS). In these studies, we find this combination preserves intact organic molecules while providing the real-time mass spectra of suspended aerosol particles. Mass spectra of particles analyzed by one-step desorption mass spectrometry and L2MS are presented for comparison. These include 2,4-dihydroxybenzoic acid as a test case and wood and cigarette combustion particles as real world examples. This is the first published demonstration of L2MS performed on single particles not deposited on a substrate prior to analysis.     

Multi-photon ionization in the mass spectrometry of polyatomic molecules: Cross sections

Multi-photon ionization (MPI) with tunable visible/UV laser light is shown to be a sensitive tool for analysis of traces in gas mixtures when combined with a mass spectrometer. Mass spectra of six different organic molecules, obtained with low intensity laser light, are presented and demonstrate the facility of ionization without fragmentation (soft ionization) under proper experimental conditions. Quantitative values for the cross sections for both two photon steps are obtained from the measured intensity dependence and the absolute ion numbers. Such quantitative data help in the evaluation and definition of this new ionization technique in mass spectrometry. Efficiencies of ionization for some molecules are as high as 25% leading to 10⁶ ions in a single pulse from the dye laser (1 kW). Detectability as low as 2 parts in 10⁹ is thus predicted.     

Mass spectral studies of some aryl and aroyl derivatives of glyoxime

Mass spectra of two diaroylglyoximes (Ia and Ib) are reported and compared with those of the corresponding dehydration products, 3,4-diaroyl-1,2,5-oxadiazoles (IIIa and IIIb, respectively). In Ia and Ib, unlike in diarylglyoximes (Id and Ie), the largest ion is [M — 18]⁺, but this does not form in the ion source by a simple thermal dehydration. Similar spectra have been obtained for an alkyl aroyl derivative of glyoxime (Ic) and an isonitroso-β-diketone (II). A specific electron-impact-induced rearrangement leading to the formation of carboxylic acids has been observed in the mass spectra of all the acylated oximes under investigation.     

An optimized procedure for detection of proteins on carrier ampholyte isoelectric focusing and immobilized pH gradient gels with imidazole and zinc salts: its application to the identification of isoelectric focusing separated isoforms by in-gel proteolysis and mass spectrometry analysis.

A method for the characterization of proteins separated by isoelectric focusing in carrier ampholytes (CA-IEF) or immobilized pH gradient (IPG) gels by in-gel digestion and mass spectrometry is described. Proteins are detected by an improved imidazole-Sodium dodecyl sulfate (SDS)-zinc staining adapted for IEF and IPG gels. Sensitivity is close to that of mass spectrometry-compatible silver staining, but simpler and faster. Proteins were digested in imidazole-SDS-zinc stained CA-IEF and IPG gels in the presence of a zinc-chelating agent. Mass spectra were clearly interpretable as carrier ampholytes which were efficiently removed before digestion; high-sequence coverage that allowed isoform characterization was obtained by analyzing both the aqueous and the organic phase extracts.     

Ionic liquid-assisted electrospray ionization of polysaccharides

In this work, we give the report of significant detection sensitivity improvement of electrospray ionization (ESI) mass spectra of polysaccharides by adding various ionic liquid compounds into samples. Mass spectra obtained were greatly simplified and appeared to be similar to spectra from matrix-assisted laser desorption/ionization due to the narrow charge number distribution. Mass spectra of polysaccharides with the attachment of either anion or cation of ionic liquid compounds were observed. No protonated or deprotonated polysaccharide ions were detected when ionic liquid compounds were added into samples. Little alkali-attached polysaccharide ions were observed. Ionic liquid-assisted ESI (ILA-ESI) mass spectrometry has significantly improved the detection sensitivity of large neutral polysaccharide compounds.     

Characterization of bis-carboxyethyl germanium sesquioxide and its complexes with amino acids using electrospray QqTOF mass spectrometry

This work deals with the application of electrospray ionization mass spectrometry (ESI-MS) with QqTOF analyzer for the characterization of Ge-132 complexes with different amino acids in aqueous solution with the emphasis on the determination of elemental composition. ESI mass spectra provide complementary structural information in both polarity modes. Some reaction products were suggested based on the interpretation of high resolution mass spectra. Moreover, the experimental isotopic distributions of ions were compared with theoretical calculated isotopic clusters. The superposition of many ion overlays was observed due to the wide isotopic distributions of studied polyisotopic complexes. The high resolution QqTOF analyzer enabled the discrimination of these ion signals differing at least by 0.12 mass units. The occurrence of overlaid signals from ions with smaller mass difference was successfully recognized based on the shift of isotopic distribution, and their elemental composition was verified using mass accuracies of non-overlaid isotopes at the borders of the isotopic cluster. Mass spectra obtained with ion trap and single quadrupole analyzers support QqTOF data.     

Analysis of organic compounds with SNMS

Summary Plasma-based Secondary Neutral Mass Spectrometry (SNMS) as a depth-resolving technique was examined for the first time as a method for the quantitative analysis of heterogeneously distributed organic compounds in environmental material. Using argon ion bombardment (340 eV, 2 mA/cm²) SNMS was applied to a variety of organic compounds. Aliphatic and aromatic hydrocarbons as well as organic compounds with heteroelements yielded mass spectra with predominant atomic signals of carbon and all other elements composing the organic compound. Except for molecularly bound chlorine and nitrogen these signals were found to be governed primarily by atomic ionization probabilities, a prerequisite for elemental quantitation with low matrix dependence. For oxygen as one of these elements matrix dependent variations of the relative detection factor of ±40% were obtained in agreement with average deviations reported for alloy samples. The organic character of the samples is manifested in the appearance of C_mH_n clusters with relative yields declining with increasing number of atoms. The CH signal turned out to be proportional to the hydrogen content regardless of the molecular structure of the compound. This is of analytical importance because low mass separation usually hampers reliable detection of atomic hydrogen with quadrupole mass filters. Other heteroelemental clusters were not detected in significant amounts.     

Design and construction of glow discharge-ion trap mass spectrometer (GD-ITMS) and its application for the analysis of volatile organic samples

In this study, we present a newly designed see-through type hollow cathode glow discharge (St-HCGD) cell developed for the analysis of volatile organic materials in an ion trap mass spectrometer. The cell was interfaced with a homemade ion trap mass spectrometer by adopting skimmer and sampler in an optimized dimensions based on the computer simulation done by SIMION software. The St-HCGD cell has a relatively small size (4×4×7 cm) with the diameter of the inner tube of 0.25′′. The anode and cathode were made of stainless steel-304 and helium was used as a buffer gas for discharge to enhance the Penning ionization process rather than sputtering process. Mass spectra of volatile organic samples such as benzene, toluene, cyclohexane were obtained by using the St-HCGD-ITMS.     

Evaluation of the potential of thermospray liquid chromatography-mass spectrometry in neurochemistry

Optimized operating conditions previously developed for the determination of neuroactive indoleamines and metabolites were adapted to meet the requirements of thermospray liquid chromatography-mass spectrometry (LC-MS) in terms of the ammonium acetate buffer system needed in this technique. Mass spectra were obtained for nineteen indolic compounds in both the positive and negative ion modes. The positive thermospray mass spectra of indoles with a free primary amino group are characterized by the base peak at [M + H]+, whereas the alcohol and acid metabolites show the base peak at [M + NH4]+. In the negative mode only amino acids and acids give good mass spectra with base peaks at [M - H + ACOOH]-. Detection limits by selected ion monitoring were of the order of 50-100 pg SIM on-column, allowing the direct determination of endogenous serotonin in an extract from rat hypothalamus. Quantitation was performed by isotope dilution MS. In the same way 5-hydroxyindoleacetic, indoleacetic, indolepropionic and indolelactic acids in urine were directly determined in an ethyl acetate extract from acidified urine samples. Likewise, gamma-aminobutyric acid and tricyclic antidepressants gave detection limits of 10 pg whereas only nanogram sensitivity could be achieved with catecholamines.     

Mass spectral evaluation of column bleeding for imidazolium-based ionic liquids as GC liquid phases

Mass spectra were obtained to evaluate the use of numerous single-cation and dicationic ionic liquids as stationary liquid phases in GC/MS at high temperature. Background mass spectra and product ion mass spectra of several ions in the background spectrum were obtained. Fragmentation mechanisms were propounded, including the detailed fragmentation pathway of the 1,2-dimethyl-3-propylimidazole cation. The relation between temperature and the main signals in the mass spectra of ILs was studied.