A new mass spectrometric classification of alkylbenzenes

A classification of alkylbenzenes is proposed based on the relative intensities of pairs of ions, of which one is formed from the other by loss of a hydrogen molecule.     

A mass spectrometric study of some dihydropyranocoumarins

Summary The mass spectra of ten angular and linear dihydropyranocoumarins without substituents and with hydroxy and acyloxy substituents in position 3 of the dimethylchroman ring have been studied. Depending on the presence and nature of these substituents the mass spectra of the compounds considered have different relative intensities of the fragments with m/e 228, 213, 176, 175, 83, and 85, which permits mass spectrometry to be used in this group of compounds for structural-analytical purposes.All-Union Scientific-Research Institute of Medicinal Plants. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 398–401, July–August, 1971.     

A rapid and efficient mass spectrometric method for the analysis of explosives

The high explosives trinitrotoluene, nitroglycerine, pentaerythritol tetranitrate and hexahydro-1,3,5-trinitro-1,3,5-triazine are efficiently ionised under negative ion atmospheric pressure chemical ionisation (APCI) conditions. The limit of detection is improved, in some cases by several orders of magnitude, by complexation with chlorine demonstrating this to be a highly suitable method for enhancing the detection capabilities for explosives. The spectra produced from introduction of the analytes in a liquid matrix, with and without chlorine present, contain a number of ions that arise through secondary processes including breakdown and adduct formation. Sample introduction into an APCI source in air, via a heated-plate inlet with a supplementary feed of dichloromethane, produces improved response for the chloride adducts of the analytes and minimises their decomposition during analysis. The tandem mass spectra produced from the chloride adducts are simple. Optimisation of the trapping parameters of the ion trap detector enhances selected transitions, yields highly reproducible spectra and improves the limits of detection for MS/MS analysis.     

A mass spectrometric study of the structure of fetidine

Chemistry of Natural Compounds -     

Amperometric method for determining the degree of complexation of polyelectrolytes with cationic surfactants

The complexation of sodium polystyrene sulfonate with monovalent cationic surfactants at a microsized liquid/liquid interface has been studied using electrochemistry. The method is based on measurement of surfactant ion transfer across the interface between two immiscible electrolyte solutions (ITIES). The complexation of various cationic surfactants (alkylpyridinium- and trimethylammonium-) with oligosized polystyrene sulfonate was measured. Binding isotherms were used to determine the degree of binding as a function of the surfactant chain length and type of head group. It was found that the hydrophobicity of the surfactant was the predominant factor. The effect of the polyelectrolyte chain length on the binding mechanism was studied using cetylpyridinium chloride as a complexing agent. It was found that binding affinity, as well as cooperativity of the binding process, decreases with decreasing polyelectrolyte chain length. Thermodynamics of surfactant binding was measured using titration microcalorimetry. The thermodynamic data obtained show that the enthalpy of surfactant binding is not dependent on polymer chain length, but an increase in chain length makes the binding process entropically more favorable.     

A mass spectrometric study of substituted furfuryl compounds

The mass spectra of six furfuryl compounds — namely, furfuryl alcohol, 5-furfuryl-furfuryl alcohol, difurfuryl ether, difurylmethane, 2,5-difurfurylfuran, and 4-furfuryl-2-pentenoic acid-γ-lactone — have been studied. Their fragmentation mechanisms are discussed in detail with particular emphasis on the modes that lead to the formation of aromatic fragments. The majority of the fragment ions are formed by elimination of CO and C₂H₂ from even-electron precursor ions and HCO from odd-electron precursor ions. Molecules containing two furan rings linked by a methylene group give mass spectra that exhibit large abundances of aromatic fragment ions.     

Hydroxyindole intermediates in the process of melanogenesis: A mass spectrometric study

Studies on the enzymatic formation of polymers from hydroxyindoles are described. FAB analysis of the reaction mixtures followed by collisional spectroscopy of the most abundant ionic species was applied to analyze products obtained from the reaction catalyzed by tyrosinase on 4- or 5-hydroxyindole at different times. Results suggest that moieties of the precursors are still present in the oligomeric systems. Among the reaction products dimeric and trimeric compounds were detected by Fast Atom Bombardment and their structure assignment was achieved by collision spectroscopy.     

A new window on fullerene chemistry: An electrospray mass spectrometric study of the amination of C60

Polyamines derived from C₆₀ were characterized by electrospray ionization mass spectrometry in 1:1 methanoltoluene containing 2.5% trifluoroacetic acid. Peak assignments are consistent with the formula C₆₀O_n(RNH₂)_m for the protonated products. The preferential formation of the hexaaminated product C₆₀O₆(RNH₂)₆ was also observed.     

Gas chromatography/combustion/isotope-ratio-monitoring mass spectrometric analysis of methylboronic derivatives of monosaccharides: a new method for determining natural 13C abundances of carbohydrates

Monosaccharides were derivatized using methylboronic acid and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA), and the delta13C values of these derivatives measured by gas chromatography/combustion/isotope-ratio-monitoring mass spectrometry to determine the original 13C-content of the monosaccharides. Comparison with the measured off-line delta13 values of the monosaccharides shows that no fractionation in 13C takes place during derivatization. The methylboronic derivatization method has proven to be a new method for natural abundance isotopic analysis of intact monosaccharides (arabinose, xylose, fucose, fructose and glucose). The method is rapid, does not involve isotopic fractionation during derivatization, and gives more precise delta13C values than other methods reported. The method was successfully applied to determine the delta13C value of glucose of the freshwater alga Scenedesmus communis.     

A mass spectrometric study of the pyrolysis of gibberellic acid

The behaviour of gibberellic acid (GA₃) under electron impact and chemical ionization conditions has been examined. The tendency of GA₃ to undergo pyrolysis by the loss of the elements of water and carbon dioxide has been identified. Two methods of sample introduction can be used to minimize the occurrence of this pyrolysis. Accurate mass measurement allows the composition of the pyrolysis product to be determined and metastable techniques confirm the structure of this product to be epi-allogibberic acid rather than its isomer allogibberic acid. This result corrects a misconception in the literature and illustrates the advantage of metastable methods compared with accurate mass measurements, for the determination of small structural differences within a molecule.     

A mass spectrometric study of the vaporization of erbium hexafluoroacetylacetonate

The sublimation of erbium tris-hexafluoroacetylacetonate Er(C₅O₂HF₆)₃ was studied by the Knudsen effusion method with the mass spectrometric determination of vapor composition. Groups of ions containing one, two, and three metal atoms were recorded. The enthalpies of sublimation of the monomeric, dimeric, and trimeric forms Δ_S H°(362 K) were found to be 133 ± 4, 135 ± 7, and 139 ± 38 kJ/mol, respectively. The melting point of Er(C₅O₂HF₆)₃ was 390 ± 2 K. No oligomeric forms were observed in vapor superheated above 430 K.     

Development of an isotope labeling ultra-high performance liquid chromatography mass spectrometric method for quantification of acylglycines in human urine

Acylglycines play a crucial regulatory and detoxification role in the accumulation of the corresponding acyl CoA esters and are an important class of metabolites in the diagnoses of inborn errors of metabolism. Sensitive quantification of a large number of acylglycines not only improves diagnosis but also enables the discovery of potential new biomarkers of diseases. We report an ultra-high performance liquid chromatography tandem mass spectrometry (UPLC–MS) method for quantifying acylglycines in human urine with high sensitivity. This method is based on the use of a newly developed isotope labeling reagent, p-dimethylaminophenacyl (DmPA) bromide, to label acylglycines to improve detection sensitivity. Eighteen acylglycines, namely acetylglycine, propionylglycine, isobutyrylglycine, butyrylglycine, 4-hydroxyphenylacetylglycine, 2-furoylglycine, tiglylglycine, 2-methybutyrylglycine, 3-methylcrotonylglycine, isovalerylglycine, valerylglycine, hexanoylglycine, phenylacetylglycine, phenylpropionylglycine, glutarylglycine, heptanoylglycine, octanoylglycine and suberylglycine, were measured. This method uses calibration standards prepared in surrogate matrix (un-derivatized urine) and stable-isotope labeled analytes as the internal standards. The analysis was carried out in the positive ion detection mode using multiple reaction monitoring (MRM) survey scans. The calibration curves were validated over the range of 1.0–500 nM. The method achieved a lower limit of quantitation (LLOQ) of 1–5 nM for all analytes, as measured by the standard derivations associated with calibration curves and confirmed in surrogate matrix; the signal-to-noise ratio at LLOQ ranged from 12.50 to 156.70. Both accuracy (% RE or relative error) and precision (% CV) were <15%. Matrix effects were minimized using the surrogate matrix. All eighteen analytes were stable in urine for at least 5 h at room temperature, autosampler (4 °C) for 24 h, 7 weeks at −20 °C and after three freeze/thaw cycles. This surrogate matrix approach was validated using a standard addition experiment. As an example of applications, the endogenous concentrations of all eighteen analytes in urine samples of 20 healthy individuals collected in three consecutive days (i.e., 60 samples) were determined; there was no significant correlation found between the acylglycine profile and gender or body mass indices.     

A new crosslinker for mass spectrometric analysis of the quaternary structure of protein complexes

Mass spectrometric structural analysis of crosslinked peptides is a powerful method to elucidate the spatial arrangement of polypeptides in protein complexes. Our aim is to develop bifunctional crosslinkers that, after crosslinking protein complexes followed by proteolytic digestion, give rise to crosslinked peptides that can be readily tracked down by mass spectrometry. To this end we synthesized the crosslinker N-benzyliminodiacetoyloxysuccinimid (BID), which yields stable benzyl cation marker ions upon low-energy collision-induced dissociation (CID) tandem mass spectrometry. Sensitive detection of the marker ion upon low-energy CID is demonstrated with different BID-crosslinked peptide preparations. With BID it becomes possible to retrieve crosslinked and crosslinker-adducted peptides, without the necessity of purifying crosslinked peptides prior to identification. The basic design of this crosslinker can be varied upon, in order to meet specific crosslinking needs.     

A new variable dispersion double-focusing plasma mass spectrometer with performance illustrated for Pb isotopes

A new generation multiple collector plasma source mass spectrometer (PSMS) produced by Nu Instruments Ltd is evaluated. The instrument has a double-focusing Nier–Johnson analyser with laminated magnet and a novel variable dispersion ion optical arrangement, enabling all masses to be located in the centre of the Faraday collectors of a fixed static array. mThe performance of the instrument has been assessed through the analysis of NBS-981 Pb using a Tl doping technique with Faraday collector efficiencies and amplifier gains determined independently. A second method of analysis involves comparison of interspersed standard and sample Pb measurements with effective gains for each collector determined from the standards. In both cases the repetition of Pb isotope measurement is competetive with the thermal ionization mass spectrometry (TIMS) double-spike method.