Chemical Ionization Mass Spectra Research Articles

Identification of Tocopherols, Tocotrienols, and Their Fatty Acid Esters in Residues and Distillates of Structured Lipids Purified by Short-Path Distillation

The fate of endogenous vitamin E isomers during production and purification of structured lipids (SLs) was investigated. Two SLs involving tripalmitin, stearidonic acid soybean oil, and docosahexaenoic acid were synthesized by transesterification catalyzed by Novozym 435 (NSL) and acidolysis by Lipozyme TL IM (LDHA) and purified by short-path distillation (SPD). The electron impact and chemical ionization mass spectra of tocopheryl and tocotrienyl fatty acid esters in the distillates measured by GC-MS in synchronous scan/SIM mode demonstrated that these esters were formed during acidolysis as well as transesterification. The predominant esters were tocopheryl palmitate, tocopheryl oleate, and tocopheryl linoleate homologues, and no tocopheryl or tocotrienyl linolenate, stearidonate, or docosahexaenoate was found. Meanwhile, none of these esters were detected in the residues for either NSL or LDHA. Less than 50% of vitamin E isomers were present in residues after SPD. This loss played a major role in the rapid oxidative deterioration of SLs from previous studies with less contribution from the formation of tocopheryl and tocotrienyl esters. The lost tocopherols and tocotrienols present at high concentration in the distillates may be recovered and used to improve the oxidative stability of SLs.

Characterization and quantification of triacylglycerols in peanut oil by off‐line comprehensive two‐dimensional liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry

The complexity of natural triacylglycerols (TAGs) in various edible oils is prodigious due to the hundreds of set is of TAG compositions, which makes the identification of TAGs quite difficult. In this investigation, the off-line 2D system coupling of nonaqueous RP and silver-ion HPLC with atmospheric pressure chemical ionization MS detection has been applied to the identification and quantification of TAGs in peanut oil. The method was successful in the separation of a high number of TAG solutes, and the TAG structures were evaluated by analyzing their atmospheric pressure chemical ionization mass spectra information. HPLC and MS conditions have been optimized and the fragmentation mechanisms of isomers have been validated. In addition, an internal standard approach has been developed for TAG quantification. Then this system was applied in peanut oil samples and there was a total of 48 TAGs including regioisomers that have been determined and quantified.

Target Urinary Analytes for the Gas Chromatographic-Mass Spectrometric Detection of Procyclidine and Benzhexol in Drug Abuse Cases

The two antiparkinsonian drugs procyclidine and benzhexol are presently finding considerable favor for their euphoric hallucinogenic effects among drug abusers in some countries. In anticipation of their possible scheduling in national drug laws, gas chromatography-mass spectrometry (GC-MS) methods for their detection in urine will be required. However, because of uncertainty of the metabolic fate of the two drugs in humans, the urinary target analytes for GC-MS detection were not well defined. The problem was addressed in the present study in which it was found that mono-hydroxy metabolites, where hydroxylation took place at the cyclohexane ring in both drugs, could be endorsed as the major target analytes. The metabolites could only be detected as the mono- and/or di-trimethylsilyl (TMS) derivatives. The predominance of either derivative depended on the temperature and time of heating with the derivatizing reagent. Because of the basic properties of the hydroxy metabolites, analytic method optimization was needed for their detection in urine included extraction under basic pH conditions. Urine hydrolysis with β-glucuronidase did not have an effect on the recovery of the metabolites, but was usually performed in search for other drugs. Because of the relative abundance of ions, the electron impact mass spectra of the mono-TMS derivatives and the chemical ionization (CI) mass spectra of the mono- and di-TMS derivatives of the hydroxy metabolites of both drugs were found to be more structurally informative. The CI mass spectra of the di- TMS derivatives have the additive advantage of being potentially useful for quantitative analysis.

A versatile electrophoric derivatisation reagent for negative ion chemical ionisation mass spectrometry: o-(pentafluorobenzyloxycarbonyl)-2,3,4,5-tetrafluorobenzoyl chloride

The synthesis of a novel electrophoric derivatisation reagent, o-(pentafluorobenzyloxycarbonyl)-2,3,4,5-tetrafluorobenzoyl chloride, is described. The reagent was tested against selected primary and secondary amino compounds, as well as phenolic and aliphatic hydroxyl compounds as analytical targets. The derivatives exhibit excellent mass spectral properties under negative ion chemical ionisation, i.e. reduced fragmentation and thus high ion current for the targeted m/z during analysis. Since the reagent bears a pentafluorobenzyl ester group, resulting negative ion chemical ionisation mass spectra were expectedly dominated by dissociative resonance electron capture typically observed with these compounds, additionally showing neutral loss of carbon dioxide and ammonia (in the case of primary amines). The reagent is suitable for detecting the target compounds with high sensitivity, as exemplified for the analysis of amphetamine and methylphenidate from human plasma where chromatographic background is drastically reduced by a shift in detected m/z and retention time and lower limits of quantification at 7.8 pg/mL (amphetamine) and 4.5 pg/mL (methylphenidate) can be obtained. The choice of two or three target quantification masses allows selective detection and adjustment of lowest background interference. No carryover effect was observed for the derivatives of amphetamine and methylphenidate.

Regio-and Stereochemical Effects in the Chemical Ionization Mass Spectra of Isomeric Bicyclo|3, 2, O| Heptan-2-One Trimethylsiloxy Derivatives1

Isomers of bicyclo |3, 2, O| heptan-2-one trimethylsiloxy derivatives, produced by (π2+π2) photocycloaddition reactions between cyclopent-2-enones and trimethylsiloxy alkenes, have been investigated by methane and isobutane chemical ionization mass spectrometry. Head-to-head and head-to-tail regioisomers and the syn-and anti-epimers in each regioisomeric set can be identified by means of these ionization methods. Prominent fragmentation patterns are discussed.

Mass spectral characteristics of the chlorinated disinfection byproduct 2,2,4-trichloro-5-methoxy-cyclopent-4-ene-1,3-dione

The objective of this paper was to correct the mistakes of a previous interpretation of electron impact ionization (EI) mass spectrum of the chlorinated disinfection byproduct (DBP) in drinking water naming 2,2,4-trichloro-5-methoxy-cyclopent-4-ene-1,3-dione (TCMCD). Moreover the positive-ion chemical ionization (CI +) and electrospray ionization (ESI +) mass spectra were also studied. As the search of new chlorinated disinfection byproducts in drinking water is a challenge and researchers generally have to attempt to identify unknown chlorinated products generated from incompletely defined starting materials, fully understanding the mass spectra of this compound may do some help for the analysis of other unknown chlorinated disinfection byproducts.

Synthesis of D- and L-Selenomethionine Double-Labeled with Deuterium and Selenium-82

The synthesis of D- and L-selenomethionine labeled with ⁸²Se and three deuteriums at Se-methyl group (D- and L-[²H₃, ⁸²Se]selenomethionine) was described. D- And L-[²H₃, ⁸²Se]selenomethionine were prepared by condensation of (R)- and (S)-2-amino-4-bromobutylic acid with lithium [²H₃, ⁸²Se]methaneselenolate, which was prepared from metal (82)Se and [²H₃]methyl iodide. The optical purities of D- and L-[²H₃, ⁸²Se]selenomethionine were determined by HPLC with a chiral stationary phase column and were found more than 99% ee. The chemical ionization mass spectra showed that the molecular related ion for N-isobutyloxycarbonyl ethyl ester derivatives of [²H₃, ⁸²Se]selenomethionine did not overlap with the m/z values known from that of non-labeled selenomethionine.

12H-Quinoxalino[2,3-b][1,4]benzothiazine derivatives as novel visible photosensitizers in cationic photopolymerization

Photoredox pairs consisting of dyes based on a 12H-quinoxalino[2,3-b][1,4]benzothiazine skeleton and iodonium salt are found to be effective initiation systems for cationic polymerization of epoxide monomers and tetrahydrofuran using VIS light. The efficiency of these initiator systems is discussed on the basis of the free energy change for electron transfer from benzothiazine dyes to the iodonium compounds. Three products, phenyl derivatives of dye 1 were isolated after photolysis of 1/onium salt system. These compounds were characterising by chemical ionization mass spectra. The reactions created the phenylated analogues of dye 1 and protons were proposed.

Characterization of prenylflavonoids and hop bitter acids in various classes of Czech beers and hop extracts using high-performance liquid chromatography–mass spectrometry

Hops contain a wide range of polyphenolic compounds with antioxidant properties divided in various chemical classes. These compounds are detected in hop extracts and also in beer as its main product. Based on the careful optimization of column type, column packing, mobile phase composition and gradient steepness, two high-performance liquid chromatography–mass spectrometry (HPLC/MS) methods have been developed. The first method using Purospher Star RP-8e column and the gradient of aqueous acetonitrile containing 0.3% formic acid is optimized for the separation of low polar polyphenolic compounds, while the second one with Zorbax SB-CN column is used for more polar hops and beer components. In this work, more compounds are detected in comparison to previous reports. In total, 49 low polar and 37 polar compounds are detected in studied samples and their molecular weights are determined based on atmospheric pressure chemical ionization (APCI) mass spectra. Some compounds are identified based on the interpretation of their full scan and tandem APCI mass spectra, retention behavior and UV spectra, while the full structure elucidation of other species still requires further research. The quantitation of xanthohumol related prenylflavonoids and bitter acids is done with two detection techniques (APCI-MS and UV detection) providing comparable results. Both compound classes (i.e., prenylflavonoids and bitter acids) are separated and quantitated in a single HPLC run, where numerous other polyphenolics are detected as well.

Identification and Structural Elucidation of Corrosion Inhibiting Long-Chain N-1-Alkyl-1,3-propanediamines by GC–MS

Gas chromatography–mass spectrometry has been used to identify long-chain (C8–C18) N-1-alkyl-1,3-propanediamines after derivatization with trifluoroacetic anhydride. Electron impact ionization and negative chemical ionization mass spectra of trifluoroacetylated derivatives of the identified N-1-alkyl-1,3-propanediamines are presented for the first time. The corrosion inhibiting long-chain N-1-alkyl-1,3-propanediamines were applied in the preparation and investigation of a new anticorrosive and antifouling formulation for water–steam circuit of energy systems in the power industry. Using the GC–MS data, it was possible to identify residues of the N-1-alkyl-1,3-propanediamines in complex samples of boiler water from the power plant after solid-phase extraction and acylation.

Metabolite analysis of human fecal water by gas chromatography/mass spectrometry with ethyl chloroformate derivatization

Fecal water is a complex mixture of various metabolites with a wide range of physicochemical properties and boiling points. The analytical method developed here provides a qualitative and quantitative gas chromatography/mass spectrometry (GC/MS) analysis, with high sensitivity and efficiency, coupled with derivatization of ethyl chloroformate in aqueous medium. The water/ethanol/pyridine ratio was optimized to 12:6:1, and a two-step derivatization with an initial pH regulation of 0.1 M sodium bicarbonate was developed. The deionized water exhibited better extraction efficiency for fecal water compounds than did acidified and alkalized water. Furthermore, more amino acids were extracted from frozen fecal samples than from fresh samples based on multivariate statistical analysis and univariate statistical validation on GC/MS data. Method validation by 34 reference standards and fecal water samples showed a correlation coefficient higher than 0.99 for each of the standards, and the limit of detection (LOD) was from 10 to 500 pg on-column for most of the standards. The analytical equipment exhibited excellent repeatability, with the relative standard deviation (RSD) lower than 4% for standards and lower than 7% for fecal water. The derivatization method also demonstrated good repeatability, with the RSD lower than 6.4% for standards (except 3,4-dihydroxyphenylacetic acid) and lower than 10% for fecal water (except dicarboxylic acids). The qualitative means by searching the electron impact (EI) mass spectral database, chemical ionization (CI) mass spectra validation, and reference standards comparison totally identified and structurally confirmed 73 compounds, and the fecal water compounds of healthy humans were also quantified. This protocol shows a promising application in metabolome analysis based on human fecal water samples.

Quadrupole ion traps

The extraordinary story of the three-dimensional radiofrequency quadrupole ion trap, accompanied by a seemingly unintelligible theoretical treatment, is told in some detail because of the quite considerable degree of commercial success that quadrupole technology has achieved. The quadrupole ion trap, often used in conjunction with a quadrupole mass filter, remained a laboratory curiosity until 1979 when, at the American Society for Mass Spectrometry Conference in Seattle, George Stafford, Jr., of Finnigan Corp., learned of the Masters' study of Allison Armitage of a combined quadrupole ion trap/quadrupole mass filter instrument for the observation of electron impact and chemical ionization mass spectra of simple compounds eluting from a gas chromatograph. Stafford developed subsequently the mass-selective axial instability method for obtaining mass spectra from the quadrupole ion trap alone and, in 1983, Finnigan Corp. announced the first commercial quadrupole ion trap instrument as a detector for a gas chromatograph. In 1987, confinement of ions generated externally to the ion trap was demonstrated and, soon after, the new technique of electrospray ionization was shown to be compatible with the ion trap.

Reversed-phase liquid chromatography-mass spectrometry of some organic tellurium compounds

The chromatographic behavior of some organic tellurium compounds (OTCs) was studied under the conditions of high-performance liquid chromatography with mass spectrometric detection. The retention characteristics (retention factor, relative retention, and differential molar Gibbs energy difference) of the compounds were obtained under the conditions of gradient elution reversed-phase liquid chromatography. The chemical ionization mass spectra of OTCs at atmospheric pressure were considered. It was shown that there was a relation between the structure of the compounds studied and their chromatographic retention.

Synthesis, spectral characterization of the zinc(II) mixed-ligand complexes of N(4)-allyl thiosemicarbazones and N, N, N′, N′-tetramethylethylenediamine, and crystal structure of the novel [ZnL 2( tmen)] compound

Mixed-ligand zinc complexes with N, N, N′, N′-tetramethylethylenediamine ( tmen) and R-salicylaldehyde N(4)-allyl thiosemicarbazones (R: 3-OCH 3 (L 1), 5-Br(L 2)), [ZnL 1,2( tmen)], were synthesized and the complexes were characterized by elemental analysis, atomic absorption spectrometer, magnetic susceptibility, molar conductivity, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) mass spectra and IR, UV–Vis, 1H NMR and 15N spectroscopies. Crystal of [ZnL 2( tmen)] have a slightly distorted square pyramid involving O, N, S atoms of thiosemicarbazone and one N atom of tmen in basal plane and the other N atom of tmen in apex of the pyramid. The non-coordinated allyl group is disordered.

Mass spectral studies of perfluorooctane sulfonate derivatives separated by high‐resolution gas chromatography

The mass spectral characteristics of perfluorooctane sulfonate (PFOS, C(8)F(17)SO(3)-) isomers present in technical PFOS were obtained using high-resolution gas chromatography (HRGC) combined with mass spectrometry (MS). To make PFOS amenable to HRGC separation, a simple derivatization procedure was developed. The method involved the conversion of PFOS into the iso-propyl ester using iso-propanol as the derivatization reagent under acidic conditions. Mass spectra were generated employing electron ionization (EI) and negative chemical ionization (NCI). Interpretation of fragment ions was possible due to the use of deuterium-labeled iso-propanol as derivatization reagent, which induced mass shifts in the electron ionization (EI) and negative chemical ionization (NCI) mass spectra. HRMS allowed the accurate mass measurement of important EI fragments and confirmed the derivatization reaction as well as the proposed fragmentation pathway involving rearrangement. Moreover, the high resolution provided by HRGC enabled the separation of eleven PFOS isomers present in the technical product. This is an improvement over the previously reported high-performance liquid chromatography (HPLC) separation. A complete identification of all isomers was not possible due to lack of pure reference materials. Finally, the developed derivatization procedure was successfully applied to perfluoroalkyl carboxylates (PFCA) and corresponding fragmentation involving rearrangement of the derivatized PFCA was observed. The described qualitative derivatization offers a promising alternative technique for the separation and identification of isomers of perfluoroalkyl sulfonates and carboxylates by HRGC/MS.

Characterization of ( E, E)-farnesol and its fatty acid esters from anal scent glands of nutria ( Myocastor coypus) by gas chromatography–mass spectrometry and gas chromatography–infrared spectrometry

Several volatile compounds, including terpenoids, fatty alcohols, fatty acids and some of their esters, were identified from solvent extracts prepared from anal scent glands of nutria (a.k.a. coypu), a serious rodent pest ravaging wetlands in the USA. The major terpenoid constituents were identified as ( E, E)-farnesol and its esters by a comparison of their gas chromatographic retention times, and electron-ionization (EI) and chemical-ionization (CI) mass spectra with those of authentic compounds. EI mass spectra of the four farnesol isomers are very similar, however, the ChemStation (Agilent) and GC–MS Solution (Shimadzu) software algorithms were able to identify the natural compound as the ( E, E) -isomer, when a high-quality mass spectral library was compiled from reference samples and used for searching. Similarly, the esters were identified as those of ( E, E) -farnesol. In contrast to EI spectra, the CI spectra of the ( E, E)- and ( E, Z)-isomers are distinctly different from those of the ( Z, E)- and ( Z, Z)-isomers. The intensities ( I) of the peaks for the m/ z 137 and 121 ions in the CI spectra offer a way of determining the configuration of the C-2 double bond of farnesols (for 2 E isomers I 137 > I 121, whereas for 2 Z isomers I 137 < I 121). Moreover, the infrared spectrum of the ( E, E)-isomer is distinctly different from those of the other three isomers in the 2962–2968 cm −1 and 2918–2922 cm −1 bands, which represent asymmetric CH 3 and CH 2 stretching vibrations, respectively. Finally, the GC retention indices of farnesol and farnesyl ester isomers determined from authentic samples were used to confirm all identifications.

Identification and quantitative determination of 5-methoxy-N,N-di-n-propyltryptamine in urine by isotope dilution gas chromatography-mass spectrometry

A simple method for analysis of 5-methoxy-N,N-di-n-propyltryptamine (5-MeO-DPT) in urine has been developed using gas chromatography-mass spectrometry (GC-MS) with tetradecadeuterated 5-MeO-DPT as internal standard, which is useful for discrimination from 5-methoxy-N,N-diisopropyltryptamine (5-MeO-DIPT). These tryptamine designer drugs were extracted from urine with Extrelut, and derivatized with trifl uoroacetic anhydride prior to GC-MS analysis. The recovery of 5-MeO-DPT from urine was 90.7%; the calibration curve showed linearity in the range of 0.01–2.0 μg/ml. When urine samples containing two different concentrations (0.1 and 1.0 μg/ml) of 5-MeO-DPT were analyzed, the coeffi cients of variation for intraday and interday testing ranged from 3.11% to 5.82%. The established method was applied to an acute poisoning case in which 5-MeO-DIPT abuse had been suspected. Unexpectedly, 5-MeO-DIPT could not be detected, but 5-MeO-DPT was found in the subject’s urine and in an aqueous sample seized upon investigation of the poisoning; the electron-impact ionization and chemical ionization mass spectra well agreed with those of authentic 5-MeO-DPT. The concentration of 5-MeO-DPT in urine of this case was 0.37 μg/ml. Although several reports have appeared describing poisoning cases of 5-MeO-DIPT, which carries the street name “Foxy,” to our knowledge, this is the first report of GC-MS analysis of 5-MeO-DPT and demonstration of its use in a poisoning case.

Occurrence of radical molecular ions in atmospheric pressure chemical ionization mass spectra of heterocyclic compounds

Occurrence of radical molecular ions in atmospheric pressure chemical ionization mass spectra of heterocyclic compounds

Identification of corrosion inhibiting long-chain primary alkyl amines by gas chromatography and gas chromatography–mass spectrometry

Gas chromatography with flame-ionization detection (FID) and gas chromatography–mass spectrometry (GC/MS) has been used to identify long-chain primary alkyl amines after derivatization with trifluoroacetic anhydride (TFAA). Electron impact ionization (EI) and positive chemical ionization (PCI) mass spectra of trifluoroacetylated derivatives of the identified alkyl amines are presented. The corrosion inhibiting alkyl amines were applied in the investigation of a new anticorrosive and antifouling formulation for water–steam circuit of energy systems in the power industry.

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.