Chemical Ionization Mass Spectra Research Articles

Computer‐assisted interpretation of atmospheric pressure chemical ionization mass spectra of triacylglycerols

Current lipidomics approaches require simple and rapid algorithms enabling the interpretation of mass spectra of lipids. Most lipids are complex mixtures of related components in which the composition of the aliphatic fatty acid chains varies from one molecule to the next. Triacylglycerols (TAGs) are an example of such a lipid class. Fatty acid chains are the only parts of the molecule to change from one species to another. Fatty acids, and consequently also TAGs, can be characterized by two parameters; the number of carbon atoms and the number of double bonds. All calculations reflecting relations among ions in the spectra can be easily made using these parameters. An algorithm for the automated interpretation of TAGs from atmospheric pressure chemical ionization mass spectra (TriglyAPCI) is presented in this paper. The algorithm first identifies diacylglycerol fragments and molecular adducts. In the next step, relations among the ions are searched and possible TAG structures are suggested. Individual features of the algorithm are described in detail and the software performance is demonstrated for the liquid chromatography/mass spectrometric (LC/MS) analysis of TAGs isolated from the termite Prorhinotermes canalifrons.

Effects of functional groups on the fragmentation of dyes in electrospray and atmospheric pressure chemical ionization mass spectra

Electrospray ionization (ESI) is most suitable for dyes with an ionic or very polar character, while atmospheric pressure chemical ionization (APCI) suits better those dyes and pigments with low to medium polarity. The negative-ion mode of ESI is used for anionic dyes such as (poly)sulfonated and/or (poly)sulfated variants, where the series of deprotonated molecules enables an easy determination of molecular weights and the number of acid groups. The positive-ion APCI or ESI mass spectra of non-ionic and cationic dyes and pigments provide typical molecular adducts [M + H] +, [M + Na] + and [M + K] + used for the molecular assignment. The first-order mass spectra often suffer from the lack of fragment ions, which can be solved by using multistage tandem mass spectra (MS n ) measured with an ion trap analyzer. The effects of various functional groups on the fragmentation behavior are described herein. The detailed understanding of fragmentation paths enables the correlation among particular functional groups and the fragmentation patterns. The presented approach is applicable for the structural analysis of complex mixtures using HPLC/MS/MS techniques with volatile ion-pairing agents.

Mass Spectrometric Behavior of Four Typical Stemona Alkaloids

Abstract The mass spectrometric behavior of four Stemona alkaloids was studied. Electron impact (EI) mass spectra showed the molecular ion with moderate intensity [M−99] + ion as base peak. The other ions were relatively weak. EI spectra provided limited information for determination of structure of the alkaloids. However, electrospray ionization (ESI) and atmosphere pressure chemical ionization (APCI) mass spectra showed the pseudomolecular ions [M+H] + of the four compounds as base peak. The characteristic ions [M−100] + and [M−74] + corresponding to the α-methyl-γ-lactone ring were also observed . The results showed that MS 2 spectra associated with soft ionization could provide more structural information. The fragmentation pathways of the four compounds were deduced. The mass spectrometric behavior reflected their structural similarities and differences. Among all the methods, soft ionization technique is the best choice for the structural identification of Stemona alkaloid. It will serve as an important tool in the structural identification of this kind of compounds.

Solid-phase extraction-gas chromatography and solid-phase extraction-gas chromatography–mass spectrometry determination of corrosion inhibiting long-chain primary alkyl amines in chemical treatment of boiler water in water-steam systems of power plants

Gas chromatography with simultaneous flame-ionization detection (FID) and a nitrogen-phosphorus detection (NPD) as well as gas chromatography–mass spectrometry (GC/MS) has been used to characterize long-chain primary alkyl amines after derivatization with trifluoroacetic anhydride (TFAA). Electron impact ionization- (EI) and negative chemical ionization (NCI) mass spectra of trifluoroacetylated derivatives of the identified tert-octadecylamines are presented for the first time. The corrosion inhibiting alkyl amines were applied in a water-steam circuit of energy systems in the power industry. Solid-phase extraction (SPE) with octadecyl bonded silica (C 18) sorbents followed by gas chromatography were used for quantification of the investigated tert-octadecylamines in boiler water, superheated steam and condensate samples from the power plant. The estimated values were: 89 μg l −1 ( n = 5, RSD = 7.8%), 45 μg l −1 ( n = 5, RSD = 5.4%) and 37 μg l −1 ( n = 5, RSD = 2.3%), respectively.

Development of a Method for Determining Illudin S in Food by Gas Chromatography-Mass Spectrometry

A method was developed for determining illudin S, a naturally occurring toxin in the mushroom Lampteromyces japonicus in food samples with the use of gas chromatography-mass spectrometry (GC-MS). Samples of a model food, ‘Ton-jiru’ (miso soup), were spiked with authentic illudin S, which was then extracted from the samples by a two-step solvent extraction with ethyl acetate and acetonitrile-n-hexane, followed by solid phase extraction using a normal phase Bond Elut SI cartridge. The recovery of illudin S from the samples was in the range of 61‐74%. Illudin S was identified by its GC retention time and both electron and chemical ionization mass spectra. In the splitless injection mode, the calibration curves for peak area ratio of illudin S to anthracene (internal standard) were linear, in the range from 150 pg to 150 ng with correlation coefficients exceeding 0.997, and the detection limit was 36 pg per injection volume (1 µl).

Characterization of gem-difluoropropargyl synthons through HF loss from protonated molecules in methane chemical ionization mass spectra

Electron impact and methane chemical ionization mass spectra were obtained following gas chromatography/mass spectrometry for several gem-difluoropropargyl compounds, which had been synthesized as potential intermediates for synthesis of gem-difluoromethylene-containing C-3 acetylenes. EI spectra were variable with respect to the presentation of molecular ions, depending on substituent functional groups present. Methane-CI spectra were characterized by loss of 19 mass units from molecular weight with all compounds examined. These [ M − 19] + ions often presented as base peaks of the CI spectra, and were more reliably present and abundant than [ M + 1] + ions for these compounds. These ions could have been formed by elimination of HF from the protonated molecules under conditions of methane chemical ionization.

Electron ionization and methane chemical ionization mass spectrometry study of some 2,2‐disubstituted 1,3‐dioxolanes, 1,3‐dithiolanes, 1,3‐oxathiolanes and 1,3‐dioxanes. Gas‐phase lactone and thiolactone formation

AbstractThe electron ionization and methane chemical ionization mass spectra of some 2,2‐disubstituted 1,3‐dioxolanes, 1,3‐dithiolanes and 1,3‐oxathiolanes were studied. Especially, the effect of the length of the side chain in ring position 2 of these compounds and the ease of formation of possible lactone/thiolactone ion as a fragmentation product were examined. In addition, two 2,2‐disubstituted 1,3‐dioxanes were studied to see the effect of the bigger ring size. The formation of lactone ions was more favorable under methane chemical ionization than under electron ionization conditions. The structures of fragment ions and the ions generated from model compounds were carefully studied using both high‐ and low‐energy collision‐induced dissociation. Also ab initio molecular orbital calculations up to the HF/6–31G** level of theory for protonated 2‐methyl‐2‐propanoic acid ethyl ester of 1,3‐dioxolane, 1,3‐oxathiolane and 1,3‐dithiolane and for two isomeric bicyclic ions were carried out. The theoretical results obtained favor the formation of the lactone ion. Copyright © 2005 John Wiley & Sons, Ltd.

Negative Ion Chemical Ionization Mass Spectra of C1–C6 n-Alkyl Nitrates

Abstract Negative ion chemical ionization mass spectra were examined for C1–C6 n-alkyl nitrates. In contrast to peroxyacyl nitrates, NO3− ions were minor fragments. Major fragment ions were found to be NO2−, and [RO − H2]−, alkoxy counterparts from which two hydrogen atoms were eliminated. Relative intensity of the two fragment ions largely depends on the speciation, and the [RO − H2]−/NO2− ratio increases with the increasing carbon number.

Derivatization in Mass Spectrometry—5. Specific Derivatization of Monofunctional Compounds

The present paper is complementary to the foregoing reviews and describes some additional methods of the derivatization of particular functional groups mainly to enhance the structural information content of electron ionization and chemical ionization mass spectra. Derivatization approaches for the modification of unsaturated compounds, alcoholic, carboxylic, carbonyl, amine and other functional groups, are discussed. Derivatization for separation and quantitative determination of chiral enantiomeric compounds is also considered. Preliminary chemical and physicalchemical degradation for structure elucidation of high molecular weight compounds (biopolymers, synthetic polymers) is mentioned. Chemical aspects of derivatizations and characteristic mass spectral features of derivatives are described briefly. Some particular applications of chemical modification, in conjunction with mass spectral measurements for the analysis of various important bioorganic compounds and compounds in biological fluids, air, environmental etc., are considered.

Application of a liquid chromatography tandem mass spectrometry method to the analysis of water-soluble vitamins in Italian pasta

A sensitive and selective liquid chromatography tandem mass spectrometry (LC–MS/MS) method for the determination of several water-soluble vitamins, namely vitamins B 1, B 2, B 6 (pyridoxine, pyridoxal, and pyridoxamine), and PP (nicotinamide and nicotinic acid), pantothenic acid, and folic acid was developed and validated. The analytes were characterized by means of their electrospray (ESI) and atmospheric pressure chemical ionization (APCI) mass spectra. In general, the positive ion spectra were 100- to 1000-fold more intense than the corresponding negative ion ones. Chromatography of water-soluble vitamins was obtained by using a reversed-phase C16 Amide (15 cm, 5 μm) column and a mobile phase made of ammonium formate buffer (20 mM, pH 3.75)/methanol under gradient elution conditions. Linearity of the MS response was observed over three to four orders for both ESI and APCI, and limits of detection were in the low μg/l range for both the ionization techniques. In particular, the sensitivity of ESI was about two- to five-fold higher for all vitamins except PP vitamers, for which APCI produced a better response. Precision calculated at two concentration levels (0.05 and 1.0 mg/l) was within 0.2–7.4% for all intra- and inter-day determinations and for all analytes. The LC–ESI-MS/MS method was applied to the quantitative analysis of the natural content of vitamins in typical Italian pasta samples, as well as in fortified pasta samples produced for the US market.

Spectroscopic studies on Isatin-3-Semicarbazone and Isatin-3-Thiosemicarbazone

The configurations of semi-and thiosemicarbazone derivatives of isatin are assigned by means of 1H and 13C NMR Spectroscopy including NOE difference spectra, IR and electronic spectral data of these compounds are also reported and discussed. The electron impact (EI), fast atom bombardment (FAB) and negative ion chemical ionization (NICI) mass spectra are also reported. Fragmentation of molecular and pseudomolecular ions are tabulated and rationalized. KEY WORDS: IH NMR, 13C NMR, Semicarbazone thiosemicarbazone, mass spectra, negative ion chemical ionization, fragmentation. Global Jnl Pure and Applied Sciences Vol.10(4) 2004: 545-553

Metabolites of lesser grain borer in grains.

Many volatile alcohol and ester metabolites of the lesser grain borer (LGB, Rhyzopertha dominica) cultured on wheat grain were identified. Volatiles from infested samples at 80 degrees C were collected on Tenax absorbent, thermally desorbed, and analyzed by gas chromatography (GC) using infrared (IR) and mass (MS) detectors for component identification. A solid-phase microextraction (SPME) technique was used to analyze selected samples with a GC-MS system set up for obtaining chemical ionization mass spectra. SPME was also used in a synthesis process required to identify ester metabolites. Predominant compounds in LGB-infested grains were 2-pentanol and its esters of 2-methyl-2-pentenoic (A) and 2,4-dimethyl-2-pentenoic (B) acids, which are known aggregation pheromones, dominicalures 1 and 2. 2-Pentanol esters of saturated A, beta-keto- and beta-hydroxy derivatives of A and B, homologues of A and B, and acid moieties lacking the 2-methyl substitution were found. Other straight- and branched-chain secondary alcohols and their esters were also observed. Reexamination of GC-MS-IR data acquired in previous investigations of LGB cultured on sorghum grain and commercial samples in a grain odor study showed the presence of many LGB metabolites in addition to the known dominicalures.

Probing the Effects of Reagent Gas Pressure and Ion Source Temperature for Dimethyl Ether Chemical Ionization of Tricyclic Antidepressants in an External Source Ion Trap Mass Spectrometer

AbstractThis study examines the reagent gas pressure and ion source temperature dependence for dimethyl ether chemical ionization (DME CI) mass spectra recorded with an external source ion trap mass spectrometer (ITMS). Information for better controls of the reagent gas pressure in order to obtain fair CI spectra is provided. The origin of M+• ions observed in DME CIMS is discussed in detail. Furthermore, the ion source temperature effect on the DME CI is also investigated.

Stereospecific ion-molecule reactions of anabolic-type steroid tertiary alcohols with proton-donating cations.

Isobutane and methane chemical ionization (CI) mass spectra of C-17a-epimeric, 17a-substituted 3-methoxyestra-1,3,5(10),8-tetraen-17a-ols and at C-17-epimeric 17-substituted 3-methoxyestra-1,3,5(10)-trien-17-ols, as well as of some their derivatives, have been studied. In each epimeric pair, the peak intensity ratio [MH-H(2)O](+) / [MH](+) is greater for stereoisomers having an axial (or quasi-axial) hydroxyl group. The same regularity in the peak intensity ratio [MH-CH(3)COOH](+) / [MH](+) is valid for acetates in the D-homo series. The observed quantitative differences in CI mass spectra of epimers are explained by steric hindrance of the attack of the proton-donating cation caused by the angular 18-methyl group. No differences in the ease of elimination of the silanol molecule were observed in CI mass spectra of epimeric silyl ethers.

Electron ionization and atmospheric pressure photochemical ionization in gas chromatography-mass spectrometry analysis of amino acids.

The mass spectra of tert-butyldimethylsilyl (TBDMS) derivatives of 17 amino acids were obtained using electron ionization (EI) and atmospheric pressure photochemical ionization (APPhCI) mass spectrometry. The APPhCI mass spectra for all of the derivatives except arginine were shown to consist of only molecular [M](+.) and quasimolecular [MH](+) ions whereas, in the case of EI, the compounds in question underwent a drastic fragmentation. The application of APPhCI to gas chromatography-mass spectrometry enables a reliable identification of the TBDMS derivatives of amino acids in a mixture, even if its components are only partially resolved, due to the unique molecular masses for each compound. Comparison of the respective positive-ion chemical ionization (PICI) mass spectra available in the literature with APPhCI spectra has shown that, in the case of PICI, unlike APPhCI, noticeable fragmentation occurs.

Solid phase microextraction (SPME) combined with gas-chromatography and olfactometry-mass spectrometry for characterization of cheese aroma compounds

The applicability of solid phase microextraction (SPME) as a technique for the concentration of cheese aroma for analysis by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) was assessed in this preliminary study. Three each of the following cheese varieties were examined: cheddar, hard grating and mold-ripened blue. Volatile components were concentrated by Carboxen-PDMS SPME fibres for 16 h (overnight) and analysed by GC-MS and GC-O. Odor compounds, which could be perceived at the olfactory port (OP), were matched with electron impact (EI) and methanol chemical ionization (CI) mass spectra. The volatile compounds identified were compared to previously reported cheese aroma compounds. Of the components identified via olfactometry, methanethiol, methional, dimethyl trisulfide and butanoic acid were present in all of the cheeses implying their essential role in the formation of basic cheese aroma. A number of alkyl-pyrazines were also found to impart roasted nutty, raw potato and savoury broth-like notes in some of the cheeses. In all cases, the aroma active compounds identified via olfactometry were in agreement with those reported in the literature. In a separate study, it was demonstrated on a number of cheeses that the adsorption of most important aroma volatiles increased consistently up to 16 h; i.e. sulfur compounds, lactones, pyrazines, phenolic compounds and benzene derivatives. For the strong-smelling pecorino and blue cheeses, however, some analyte displacement effects were observed. Data indicated that a sampling time between 9 and 16 h was appropriate and displacement/competition reactions tended to occur in strong cheeses, i.e. those which have undergone extensive lipolysis e.g. pecorino, very high concentration of butanoic and hexanoic acid, and/or β-oxidation e.g. blue cheese, with high concentrations of 2-heptanone and 2-nonanone.

L-Methionine Ethyl Ester 유도체의 구리 이가 착물 합성 및 구조 분석

O fashion andmaintains its chirality upon coordination.EXPERIMENTALMaterials and Methods. Reagents and solventsused were of commercially available reagent gradequality unless otherwise stated. Anhydrous diethyl etherwas distilled from sodium/benzophenone under argon.Elemental analysis (C, H, N) were performed bythe Elemental Analysis Laboratory of the KoreanBasic Science Institute. Chemical ionization massspectra were obtained on a double-focusing Vac-uum Generator 70-S (VG-70S) gas chromatography/mass spectrometer. Infrared spectra were recordedon a KBr plate with a PE Biosystem FT-IR spec-trometer.

Reaction of 1-alkyl/aryl-3-amino-1 H,3 H-quinoline-2,4-diones with urea. Synthetic route to novel 3-(3-acylureido)-2,3-dihydro-1 H-indol-2-ones, 4-alkylidene-1′ H-spiro[imidazolidine-5,3′-indole]-2,2′-diones, and 3,3a-dihydro-5 H-imidazo[4,5- c]quinoline-2,4-diones

1-Substituted 3-alkyl/aryl-3-amino-1 H,3 H-quinoline-2,4-diones react with urea in boiling acetic acid to give products depending on the type of substitution in position 3 and at the nitrogen atom of the 3-amino group. Starting compounds bearing a primary amino group in position 3 give 3-(3-acylureido)-2,3-dihydro-1 H-indol-2-ones. Starting compounds bearing a secondary amino group in position 3 react according to the character of the other substituent in position 3. If there is a hydrogen atom α to the carbon atom C(3), 4-alkylidene-1′ H-spiro[imidazolidine-5,3′-indole]-2,2′-diones arise. If a hydrogen atom is not present in this position, the reaction leads to 3,3a-dihydro-5 H-imidazo[4,5- c]quinoline-2,4-diones. Reaction mechanisms for these transformations are proposed. All compounds were characterized by their 1H, 13C, IR and atmospheric pressure chemical ionization mass spectra and some of them also by 15N NMR data.

Cluster chemical ionization for improved confidence level in sample identification by gas chromatography/mass spectrometry.

Upon the supersonic expansion of helium mixed with vapor from an organic solvent (e.g. methanol), various clusters of the solvent with the sample molecules can be formed. As a result of 70 eV electron ionization of these clusters, cluster chemical ionization (cluster CI) mass spectra are obtained. These spectra are characterized by the combination of EI mass spectra of vibrationally cold molecules in the supersonic molecular beam (cold EI) with CI-like appearance of abundant protonated molecules, together with satellite peaks corresponding to protonated or non-protonated clusters of sample compounds with 1-3 solvent molecules. Like CI, cluster CI preferably occurs for polar compounds with high proton affinity. However, in contrast to conventional CI, for non-polar compounds or those with reduced proton affinity the cluster CI mass spectrum converges to that of cold EI. The appearance of a protonated molecule and its solvent cluster peaks, plus the lack of protonation and cluster satellites for prominent EI fragments, enable the unambiguous identification of the molecular ion. In turn, the insertion of the proper molecular ion into the NIST library search of the cold EI mass spectra eliminates those candidates with incorrect molecular mass and thus significantly increases the confidence level in sample identification. Furthermore, molecular mass identification is of prime importance for the analysis of unknown compounds that are absent in the library. Examples are given with emphasis on the cluster CI analysis of carbamate pesticides, high explosives and unknown samples, to demonstrate the usefulness of Supersonic GC/MS (GC/MS with supersonic molecular beam) in the analysis of these thermally labile compounds. Cluster CI is shown to be a practical ionization method, due to its ease-of-use and fast instrumental conversion between EI and cluster CI, which involves the opening of only one valve located at the make-up gas path. The ease-of-use of cluster CI is analogous to that of liquid CI in ion traps with internal ionization, and is in marked contrast to that of CI with most other standard GC/MS systems that require a change of the ion source.

Unprecedented reactivity of 3-amino-1 H,3 H-quinoline-2,4-diones with urea: an efficient synthesis of 2,6-dihydro-imidazo[1,5- c]quinazoline-3,5-diones

Substituted 3-amino-1 H,3 H-quinoline-2,4-diones react with urea in acetic acid to give novel 2,6-dihydro-imidazo[1,5- c]quinazoline-3,5-diones in high yields. The same compounds were obtained, albeit with small yields, from 3-chloro-1 H,3 H-quinoline-2,4-diones and urea. In the proposed reaction mechanism, a molecular rearrangement of the primarily formed mono-substituted urea takes place. The prepared 2,6-dihydro-imidazo[1,5- c]quinazoline-3,5-diones were characterized by their 1H, 13C, 15N NMR and IR spectra and atmospheric pressure chemical ionisation mass spectra.