Identification of amino acid thiohydantoin derivatives by chemical ionization mass spectrometry

The chemical ionization mass spectra of 16 amino acid thiohydantoins were examined using isobutane or ammonia as reagent gases. Except for a few cases, including some aromatic amino acids, the chemical ionization spectra were much simpler than the corresponding electron impact spectra. Therefore, the major component in the amino acid thiohydantoin mixture was easily detected by chemical ionization mass spectrometry. The combination of the chemical ionization method and thiohydantoin formation was applied successfully to the sequence analysis of model peptides.     

Comparison by mass spectrometry of ring cleavage in barbituric acid and 5-fluorobarbituric acid derivatives

The mass spectrometric behaviour of barbituric acid and 1,3-dimethylbarbituric acid was compared with that of the corresponding 5,5-difluoro derivatives and of some 5-fluoro-5-alkyl derivatives in order to study the influence of fluorine in the fragmentation processes. This investigation, performed using both electron impact ionization and positive- and negative-ion fast atom bombardment, evidences well the role of fluorine in barbiturate ring bond cleavages.     

High sensitivity analysis of phenylthiohydantoin amino acid derivatives by electrospray mass spectrometry

A new methodology has been developed for high sensitivity electrospray ionization mass spectrometric analyses of phenylthiohydantoin (PTH) amino acid derivatives. Key components of the methodology are the use of a solvent system consisting of methanol/dichloromethane (1:1 v/v) containing 5-mM lithium triflate, a stainless steel electrode having a relatively large surface area, and a microscale electrospray nozzle that provides for stable electrospray at flow rates in the range of 100–500 nL/min. A linear response for the absolute signal intensity of the protonated molecule was observed for a number of derivatives over the concentration range of 50–1000 fmol/µL. For all except the arginine derivative, there was a decrease in the signal intensity with increasing flow rate with 100–300 nL/min being optimum. Collision induced dissociation (CID) product ion spectra were obtained for 21 derivatives including carboxymethyl cysteine and dehydrothreonine. Leucine and isoleucine can be distinquished on the basis of their CID product ion spectra. A subfemtomole detection limit was demonstrated for the phenylalanine PTH derivative in a selected reaction monitoring (SRM) experiment. Samples from an automated Edman microsequencer run have been analyzed using the new technique and compared to results obtained by conventional high-performance liquid chromatography analysis with UV detection. This work demonstrates the feasibility of using mass spectrometry to identify and quantitate the products generated by automated protein microsequencing using standard Edman degradation chemistry.     

Identification of dimethylarsinoyl-riboside derivatives in seaweed by pneumatically assisted electrospray tandem mass spectrometry

Pneumatically-assisted electrospray tandem mass spectrometry (ES MS/MS) was proposed as a technique for the identification of dimethylarsinoyl-riboside derivatives (arsenosugars) in seaweed (Laminaria). Conditions for the acquisition of MS and MS/MS spectra were optimized. A size-exclusion HPLC (SE HPLC) step was developed for the purification of algal extracts prior to ES MS. The arsenosugar fraction was found to elute prior to the majority of other arsenic compounds. The identity of the compounds expected to be arsenosugar compounds was confirmed by the collision induced dissociation (CID) of the relevant protonated molecule ions. An independent confirmation of the identity of analytes was obtained by two-dimensional (size-exclusion–anion exchange) HPLC–ICP MS with signal identification by spiking with the appropriate arsenosugar standards.     

Detection and identification of alkylphosphonic acids by positive electrospray ionization tandem mass spectrometry using a tricationic reagent

The retrospective detection and identification of degradation products of chemical warfare agents are of immense importance in order to prove their spillage and use. A highly sensitive liquid chromatography/electrospray ionization tandem mass spectrometric (LC/ESI-MS/MS) method--using an imidazolium-based tricationic reagent--was developed for the detection and identification of the anionic degradation products of nerve agents. A commercially available solution of 1,3-imidazolium-bis-(1-hexylbenzylimidazolium) trifluoride (IBHBI) formed adducts with alkylphosphonic acids (APAs), allowing detection of the APAs by positive mode ESI-MS. Tandem mass spectrometry was used for the unambiguous identification of the APAs. Parameters influencing the formation and stability of these adduct during mass spectrometric analysis, such as solvent composition, concentration of IBHBI, effect of pH and interferences by salts, were optimized. The absolute limits of detection (0.1 ng) for achieved for the APAs were better than those previously reported, and linear dynamic ranges of 10-2000 ng mL(-1) were achieved. The method was repeatable with a relative standard deviation ≤7.3%. APAs present in aqueous samples provided by the Organization for the Prohibition of Chemical Weapons during the 22(nd) and 24(th) Official Proficiency tests were detected and identified as IBHBI adducts. The added advantage of this method is that low-mass analytes are detected at higher mass, thus obviating the problem with background noise at low mass.     

Identification and quantification of oleanolic acid and ursolic acid in Chinese herbs by liquid chromatography-ion trap mass spectrometry

A rapid and sensitive method for the identification and quantification of ursolic acid (UA) and oleanolic acid (OA) in Chinese herbs is described. The method combines liquid chromatography (LC) with ion trap‐mass spectrometry (IT‐MS) detection. The UA and OA standard solution were directly infused into IT‐MS for collecting MSⁿ spectra. The major fragment ions of UA and OA were confirmed by MSⁿ at m/z 455, 407, 391, 377 and 363 in negative ion mode, and m/z 457, 439, 411 and 393 in positive mode, respectively. The possible main cleavage pathway of fragment ions was studied. UA and OA provided good signals corresponding to the deprotonated molecular ion [M − H]⁻. The method is reliable and reproducible, and the detection limit is 5 ng/mL. The method was validated in the concentration range of 0.04–40 μg/mL; intra‐ and inter‐day precisions ranged from 0.78 to 2.15%, and the accuracy was 96.5–108.2% for UA and OA. The mean recovery of UA and OA was 97.1–106.2% with RSD less than 1.86%. An LC‐IT‐MS method was successfully applied to determine the UA and OA in nine Chinese herbs. Copyright © 2011 John Wiley & Sons, Ltd.     

A study of santonins and their derivatives by mass spectrometry

Fragmentation patterns of santonins and their derivatives under electron impact have been investigated by th use of high resolution mass spectra and a deuterium labelling technique. The relationship between conformation of santonins and their spectra is discussed.     

Identification of butyryl derivatives of cyclic nucleotides by positive ion fast atom bombardment mass spectrometry and mass-analysed ion kinetic energy spectrometry

The syntheses of the dibutyryl derivatives of the 3′,5′-cyclic monophosphates of adenosine, guanosine and cytidine are described. The fast atom bombardment mass spectra of these compounds are discussed, together with the mass-analysed ion kinetic energy spectra of their protonated molecular ions and of diagnostic fragments. A protocol for the identification of the derivatives is reported which includes criteria for confirming retention of the cyclic phosphodiester moiety, substitution of both heterocyclic base and ribose ring, and butyrylation of the 2′-O-position. The origins of significant fragments in the spectra are discussed.     

Identification of polyethanolamines by chromatography–mass spectrometry

Presumable structures of polyethanolamines, synthesized by the catalytic β-hydroxyethylation of ammonia with an excess of ethylene oxide are determined by gas chromatography–electron ionization mass spectrometry and tandem mass spectrometry qualitatively, following fragmentation ways and also taking into account retention data. The preferable paths of consecutive reactions of the synthesis of polyethanolamines in a homologous series of isomers are found.     

Identification of caffeic acid derivatives in Actea racemosa (Cimicifuga racemosa,black cohosh) by liquid chromatography/tandem mass spectrometry

Caffeic acid derivatives occurring in black cohosh [Cimicifuga racemosa (L.) Nutt., Actaea racemosa (Ranunculaceae)], some of which may have pharmacological activity, were analyzed using high-performance liquid chromatography (HPLC) electrospray ionization tandem mass spectrometry (ESI-MS/MS) with the aim of developing a methodology for their rapid identification in a complex plant matrix. Based on these studies, structurally characteristic product ions and neutral molecule losses were identified, which were then used during LC/MS/MS with product ion scanning, precursor scanning and constant neutral loss scanning to detect caffeic acid derivatives in a crude extract of black cohosh. Several caffeic acid derivatives were detected, and the identification of six of them were confirmed by comparison with authentic standards including caffeic acid, ferulic acid, isoferulic acid, fukinolic acid, cimicifugic acid A, and cimicifugic acid B. Four other compounds were detected that appeared to be caffeic acid derivatives based on LC/MS/MS retention times, molecular weights, and fragmentation patterns during MS/MS. Since standards were unavailable for these four compounds, they were tentatively identified using LC/MS/MS as cimicifugic acid E, cimicifugic acid F, dehydrocimicifugic acid A, and dehydrocimicifugic acid B. Dehydrocimicifugic acid A and dehydrocimicifugic acid B have not been reported previously to be constituents of black cohosh.     

Identification of derivatives of 2H-chromenes and their acyclic tautomeric forms in the gas phase by mass spectrometry

It was established that mass spectrometry makes it possible to identify in the gas phase molecular ions with both the 2H-chromene structure and their acyclic tautomers from the characteristic (M-OH)⁺ and (M-ArNH)⁺ fragment ions, respectively. The fragmentation scheme was confirmed by methods involving dissociation of ions activated by collision and deuterium labeling. Measurement of the ionization energies of the investigated compounds makes it possible to exclude the possibility of the existence in the gas phase of a tautomeric form with an o-quinoid structure.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 746–750, June, 1988.     

超高效液相色谱-串联质谱法鉴定与分析乙醛诱导脱氧核糖核苷酸加合物

采用超高效液相色谱-串联质谱法对两种非对映异构体（6S,8S）1,N²-丙基-2'-脱氧鸟苷（ProdG）和（6R,8R）ProdG加合物进行鉴定与分析。通过色谱保留时间及质谱碎裂方式分析,证明乙醛与2'-脱氧鸟苷（dG）反应可形成ProdG加合物。体外实验表明,乙醛能够诱导脱氧核糖核苷酸（DNA）形成ProdG加合物,并且（6R,8R）ProdG的生成量大于（6S,8S）ProdG的生成量。细胞实验结果显示,乙醛暴露能显著提高人肺胚成纤维细胞（MRC5）基因组DNA中ProdG加合物的水平,且ProdG加合物的水平与乙醛的暴露浓度呈正相关。此外,100 μ mol/L的乙醛暴露使（6R,8R）ProdG的含量从（6.4±0.3） 个/10⁸个碱基增加到（127.2±2.7） 个/10⁸个碱基,上调程度大于（6S,8S）ProdG（从（6.5±0.3） 个/10⁸个碱基增加到（115.3±2.5） 个/10⁸个碱基）。该工作为乙醛暴露所引起的DNA加合物水平上升提供了实验依据。     

Determination of alkyl alkylphosphonic acids by liquid chromatography coupled with electrospray ionization tandem mass spectrometry using a dicationic reagent

A new analytical method based on liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS) is proposed and validated for the identification and quantification of alkyl alkylphosphonic acids (AAPAs) in aqueous matrices. Retrospective detection and identification of degradation products of chemical warfare agents is important as an indicator of possible use of chemical warfare agents or of environmental contamination. A commercially available solution of 1,9‐nonanediyl‐bis‐(3‐methylimidazolium)bisfluoride (NBMI) allowed detection of AAPAs by positive mode electrospray ionization mass spectrometry by forming an adduct with AAPAs. MS/MS experiments using an ion trap analyzer were carried out for unambiguous identification of AAPAs. Different parameters were optimized in order to obtain both an adequate chromatographic separation and a high sensitivity using experimental design methodology. Quantification was done with matrix‐matched calibration standards of AAPAs. The method was validated in terms of linearity (r² >0.982), intra‐ and inter‐day precisions (RSD below 15%), and robustness. The method is sensitive enough for the determination of AAPAs in aqueous matrices, with limits of detection in the 1–5 ng mL^–1 range and limits of quantification in the 5–20 ng mL^–1 range. Finally, the method was successfully applied to determine these AAPAs in aqueous samples provided by the Organization for the Prohibition of Chemical Weapons during 26^th and 29^th official proficiency tests. The added advantage of this method is identification of low mass range analyte at high mass range, which obviates the background noise at low mass range. Copyright © 2012 John Wiley & Sons, Ltd.     

Identification of tellurium-containing compounds by means of mass spectrometry

A general mass spectrophotometric method for the identification of tellurium-containing compounds is described. The method is based on the analysis of the typical pattern of cluster peaks containing tellurium due to -Te-, -Te₂- or

(X = Cl, Br). A comparison of the computer calculated and experimental mass spectra of some of the compounds containing tellurium is given.     

Adduct formation in electrospray ionization mass spectrometry II. Benzoic acid derivatives

This work serves as a follow-up to Part I of experiments designed to determine the underlying principles in the formation of pseudomolecular, or adduct, ions during electrospray ionization. Aromatic acids were studied by flow injection analysis in the negative ionization mode of electrospray ionization mass spectrometry. Part I dealt with common acidic anti-inflammatory pharmaceuticals. such as ibuprofen and related analogues. Part II deals with functionally less complex molecules, namely benzoic acid (BA) and substituted benzoic acids. Halide-substituted molecules are investigated to deduce the effect of electron-withdrawing substituents (bromo-, chloro-, and fluoro-) and ring position (ortho-, meta- and para-) on the response of a traditional deprotonated molecular ion ([M-H]-) and a sodium-bridged dimer ion ([2M-2 H+Na]-). Amino-substituted benzoic acids are also analyzed in order to study the effect of an additional ionizable group on the molecule, and para-tert.-butyl-BA is analyzed to study the effect of increased hydrophobicity, as they relate to the formation of pseudomolecular ions. This study shows that solution character [octanol-water partition coefficient (or log P) and pKa] of the model compounds controls the relative efficiency of formation of [M-H]- and [2M-2H+Na]- ions. However the relative gas phase character (gas phase basicity and proton affinity) also has a significant effect on the formation of the sodium-bridged dimer ion. For the halide-substituted species, placement of the electron-withdrawing atom at the meta-position gives the greatest enhancement in sensitivity. Observations also show that as the structural complexity of the model compound increases, predictions relating analyte acidity to sodium-bridged dimer ion formation give way to a stronger dependence between log P values and ionization efficiency. Supporting this hypothesis is the nearly ten-fold enhancement in signal for tert.-butyl BA relative to BA. due to the greater hydrophobicity, and consequently, increased surface activity in an electrosprayed droplet of the analyte molecule.     

Identification of 19 phthalic acid esters in dairy products by gas chromatography with mass spectrometry

A detection method for 19 kinds of phthalic acid ester compounds analyzed by n‐hexane/ether/acetonitrile 1:7:8 v/v/v mixed solvent extraction, quick, easy, cheap, effective, rugged, and safe purification and internal standard method of quantitative gas chromatography with mass spectrometry was established. This method can effectively remove interfering materials, such as lipids, fatty acids, and pigments, from dairy products. The 19 kinds of phthalic acid ester compounds were within a 0.025–0.2 mg/kg range, the recovery rate was 65.2–125.7%, relative standard deviation was 7.9–15.4% (n = 6), and the limit of detection was 0.005–0.02 mg/kg. Concentrations of the 19 kinds of phthalic acid ester compounds ranged between 0.01 and 0.12 mg/kg in ten dairy materials and 20 dairy products. The established method is simple, rapid, accurate, and highly sensitive.