Sensitivity of positive ion mode electrospray ionization mass spectrometry (ESI MS) in the analysis of purine bases in ESI MS and on-line electrochemistry ESI MS (EC/ESI MS)

A cone-shaped MS inlet and on-line electrochemistry (EC) were used to enhance the ionization efficiency in electrospray ionization mass spectrometry (ESI MS) of purine bases. A pathway of positive ion mode ESI may involve oxidation of purine bases, guanine, adenine, xanthine and hypoxanthine, by 1e⁻, 1H⁺ processes. The electrospray process generates dimers of purine bases that are detected in ESI MS as protonated ions, except for xanthine, for which a protonated radical dimer is detected. Thus electrochemical oxidation of purine bases during ESI may generate reactive radicals that can subsequently dimerize. Dimer formation is facilitated in ESI MS when the carrier solution pH is high. The positive ion mode ESI MS ionization is consistent with the reactivity of the bases toward oxidation. Furthermore, the formation of the protonated ions, and Na⁺ and K⁺ adducts of the bases, expected in positive ion ESI MS, are observed. In addition, unusual H-bonding of purine bases guanine and xanthine is confirmed by ESI MS. Application of low EC voltage to the on-line EC cell in EC/ESI MS improves the sensitivity and correlates with the decrease of the intensity of the dimers, possibly as a result of their further oxidation.     

An Improved Method for Analysis of Glucosylceramide Species Having cis-8 and trans-8 Isomers of Sphingoid Bases by LC–MS/MS

High-performance liquid chromatography–electrospray ionization tandem mass spectrometry (HPLC–ESI–MS/MS) approaches have enabled high selectivity and sensitivity for the identification and quantification of glucosylceramide molecular species. Here we demonstrate that HPLC–ESI–MS/MS is an efficient method for characterizing plant glucosylceramide species having the cis-8 and trans-8 isomers of sphingoid bases. Complete baseline separation was achieved using a high-carbon-content octadecylsilyl column and a simple binary gradient comprising methanol and water. The result of 2-hydroxy fatty acid composition achieved by HPLC–ESI–MS/MS was compared with that achieved by gas chromatography with flame ionization detection (GC–FID), indicating that the two methods yield similar molar compositions. The current method should be applicable to seeking the active components of glucosylceramide species from plant materials in response to biological challenges.     

Isoprenoid Alcohols are Susceptible to Oxidation with Singlet Oxygen and Hydroxyl Radicals

Isoprenoids, as common constituents of all living cells, are exposed to oxidative agents—reactive oxygen species, for example, singlet oxygen or hydroxyl radicals. Despite this fact, products of oxidation of polyisoprenoids have never been characterized. In this study, chemical oxidation of isoprenoid alcohols (Prenol‐2 and ‐10) was performed using singlet oxygen (generated in the presence of hydrogen peroxide/molybdate or upon photochemical reaction in the presence of porphyrin), oxygen (formed upon hydrogen peroxide dismutation) or hydroxyl radical (generated by the hydrogen peroxide/sonication, UV/titanium dioxide or UV/hydrogen peroxide) systems. The structure of the obtained products, hydroxy‐, peroxy‐ and heterocyclic derivatives, was studied with the aid of mass spectrometry (MS) and nuclear magnetic resonance (NMR) methods. Furthermore, mass spectrometry with electrospray ionization appeared to be a useful analytical tool to detect the products of oxidation of isoprenoids (ESI–MS analysis), as well as to establish their structure on the basis of the fragmentation spectra of selected ions (ESI–MS/MS analysis). Taken together, susceptibility of polyisoprenoid alcohols to various oxidizing agents was shown for the first time.     

Oxidation products of free polyunsaturated fatty acids in wheat varieties

Oxygenated fatty acids (oxylipins) are secondary metabolites of polyunsaturated fatty acids (PUFA). Here, we present a novel high‐performance liquid chromatograpic separation on a reversed‐phase column (RP‐HPLC) coupled with electrospray ionization‐tandem mass spectrometry (ESI‐MS/MS) for the determination of various (per)oxidation products of linoleic (cis,cis‐9,12‐octadecadienoic) acid in eight different varieties (four spring and four winter varieties) of wheat (Triticum aestivum). The procedure includes extraction of oxylipins, chromatograpic separation using a linear gradient of aqueous formic acid and acetonitrile, with subsequent identification of compounds by MS/MS. Among the identified oxylipins, leukotoxin (LTX)‐diol and its isomer (iso‐LTX‐diol) are known as potentially toxic substances. The obtained data was used further for comparison of different wheat varieties by principal component analysis (PCA). From the results of PCA, differences can be observed in the patterns of wheat varieties.     

高效液相色谱-电喷雾电离质谱法分析人参皂甙

利用反相高效液相色谱-电喷雾电离质谱(HPLC-ESI/MS)方法,分离分析了人参皂甙。液相色谱采用乙腈-水流动相进行梯度洗脱,质谱法利用电喷雾电离质谱(ESI/MS)研究了3种人参皂甙的一级质谱(主要给出分子量)和二级、三级质谱(提供碎片离子信息),并通过质谱图的差异对其结构进行了鉴别,建立了高效液相色谱-质谱联用法分析人参皂甙的方法。     

Characterization of silane-based hydrophobic admixtures in concrete using TOF-MS

Silane-based hydrophobic admixtures especially alkyltrialkoxysilanes are used as water repellent agents for the surface protection of concrete. To optimize the structure of alkyltrialkoxysilanes in terms of their performance and their long term durability it is important to understand the chemical reactions taking place between the silicon organic compounds and the materials on which they are applied. For this purpose the characterization of alkyltrialkoxysilanes and their reaction products in concrete is necessary. Therefore we adapted an analytical method based on time-of-flight mass spectrometry (TOF/MS) combined with electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI). Monomeric alkyltrialkoxysilanes could be analyzed by the former method, reaction products which could be identified as Silsesquioxanes (SSOs) by the latter one. The results indicate that ESI-TOF/MS and MALDI-TOF/MS serve as a reliable and convenient tool to characterize monomeric silane-based hydrophobic admixtures as well as their reaction products resulted from hydrolysis and condensation.     

Elution factors of synthetic oxotriacylglycerols as an aid in identification of peroxidized natural triacylglycerols by reverse-phase high-performance liquid chromatography with electrospray mass spectrometry

Selected elution factors were determined for model oxotriacylglycerols as an aid in identification of the peroxidation products of natural triacylglycerols by reverse-phase high-performance liquid chromatography (HPLC) with electrospray mass spectrometry (LC/ES/MS). For this purpose synthetic triacylglycerols of known structure were converted to hydroperoxides, hydroxides, epoxides, and core aldehydes and their dinitrophenylhydrazones by published procedures. The oxotriacylglycerols were resolved by normal-phase thin-layer chromatography and reverse-phase HPLC, and the identities of the oxotriacylglycerols confirmed by LC/ES/MS. Elution factors of oxotriacylglycerols were determined in relation to a homologous series of saturated triacylglycerols, ranging from 24 to 54 acylcarbons, and analyzed by reverse-phase HPLC, using a gradient of 20–80% isopropanol in methanol as eluting solvent and an evaporative light-scattering detector. It was shown that the elution times varied with the nature of the functional group and its regiolocation in the triacylglycerol molecule. A total of 31 incremental elution factors were calculated from chromatography of 33 oxygenated and nonoxygenated triacylglycerol species, ranging in carbon number from 36 to 54 and in double-bond number from 0 to 6.     

Characterisation of end groups in poly(2-hydroxyethyl methacrylate) by means of electrospray ionisation-mass spectrometry/mass spectrometry (ESI-MS/MS)

Poly(2-hydroxyethyl methacrylate) (poly(HEMA)) has been characterised by means of electrospray ionisation-mass spectrometry/mass spectrometry (ESI-MS/MS), in order to evaluate this technique for the generation of end group information. Low energy collision-induced dissociation (CID) data from poly(HEMA) enabled information on both end groups of the polymer chain to be gleaned, in a similar fashion to that proposed previously for other methacrylate polymer systems. Exact-mass CID information was employed to aid the understanding of the dissociation mechanism of the polymer. Some additional fragmentation pathways, compared to other methacrylate polymer systems, are proposed. An example of how software can aid the interpretation of the MS/MS data is also shown.     

Direct Analysis in Real Time (DART) of an Organothiophosphate at Ultrahigh Resolution by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Tandem Mass Spectrometry

Direct analysis in real time (DART) is a recently developed ambient ionization technique for mass spectrometry to enable rapid and sensitive analyses with little or no sample preparation. After swab-based field sampling, the organothiophosphate malathion was analyzed using DART-Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS) and tandem mass spectrometry (MS/MS). Mass resolution was documented to be over 800,000 in full-scan MS mode and over 1,000,000 for an MS/MS product ion produced by collision-induced dissociation of the protonated analyte. Mass measurement accuracy below 1 ppm was obtained for all DART-generated ions that belonged to the test compound in the mass spectra acquired using only external mass calibration. This high mass measurement accuracy, achievable at present only through FTMS, was required for unequivocal identification of the corresponding molecular formulae.     

Performance evaluation of porous electrocatalysts via normalization of the active surface

When comparing the rate of electrochemical processes at different porous electrocatalysts a surface normalization should be used. It is shown for the case of methanol oxidation at PtRu layers electrodeposited on gold substrates that substantially different data are obtained for current, mass spectrometry signals and integrated IR band intensities of the products, with and without normalization of the catalyst surface used. Using stripping of saturated CO coverage as a normalization tool, cyclic voltammograms, on line MS and in situ FTIR spectroscopy give reasonable agreement of catalytic activity towards methanol oxidation.On leave from: Departamento de Química, Universidade Federal do Pará, Rua Augusto Correa S/N, Belém, Pará, Brazil     

Monitoring the Epoxidation of Canola Oil by Non-aqueous Reversed Phase Liquid Chromatography/Mass Spectrometry for Process Optimization and Control

Non-aqueous reversed phase liquid chromatography/electrospray mass spectrometry (NARP-LC/ESI–MS) was used to monitor the epoxidation of canola oil by performic acid. The reaction was sampled at regular intervals over 28?h and analyzed by NARP-LC/ESI–MS in order to observe the formation of partially epoxidized reaction intermediates and the fully epoxidized products. The experiment focused on the transformation of triacylglycerols (TAG) with 54 carbons in the fatty acyl chains and between 2 and 7 double bonds which account for >93?% of the oil. NARP-LC/ESI–MS allowed determination of the time required for full epoxidation of the oil. It was shown that complete epoxidation of TAG with low numbers of double bonds occurs more rapidly than for those with many double bonds. Furthermore, it was observed that epoxidation of multiply unsaturated TAG occurs via a sequential process in which partially epoxidized intermediates are consumed to form other more highly epoxidized compounds as the reaction proceeds. Data obtained by flow-injection ESI–MS was found to be comparable to that obtained from NARP-LC/ESI–MS for monitoring intermediates and products and could be adapted for in-process reaction monitoring.     

Use of a liquid chromatograph-ion trap mass spectrometer for end-group characterization of various polyethoxylate materials

The separation and detection properties of various ethoxylated polymers were investigated with atmospheric pressure ionization liquid chromatography/mass spectrometry (LC/MS). Interesting chromatographic elution behavior based on functionality was noted. LC/MS using in-source CID (collision-induced dissociation) and tandem mass spectrometry (MS/MS) detection was compared for end-group identification. Excellent end-group identification was achieved when the end-group molecular weight (MW) was greater than 100 Da and the average MW of the polymer was less than 400 Da by both MS/MS and in-source CID. In cases where the end-group MW was less than 100 Da, because of the low mass cut-off in a quadrapole ion trap analyzer, in-source CID produced the only characteristic end-group ions. The use of a dual scan function allowed investigation of the oligomeric distribution followed by a narrow low-mass scan using in-source CID to generate end-group information. This approach is applicable on instruments without MS/MS capability.     

Comprehensive Triacylglycerol Characterization of Oils and Butters of 15 Amazonian Oleaginous Species by ESI‐HRMS/MS and Comparison with Common Edible Oils and Fats

The Amazon rain forest encompasses an extraordinary source of vegetable oils with many applications, especially for food, pharmaceutical and cosmetics industries. In this work, the main composition of fifteen Amazonian oils and butters are investigated via gas chromatography‐mass spectrometry (GC‐MS) and electrospray ionization high resolution mass spectrometry (ESI‐HRMS). Triacylglycerols (TAG) are characterized by their fragmentation spectra and comparison with the LIPID MAPS database, resulting in a detailed compendium of TAG composition of these samples. Over 70 different TAG are putatively annotated per sample and the occurrence of isomers is remarkable, showing that TAG complexity in these samples is considerably higher than ever reported. The TAG composition of the Amazonian samples are also statistically evaluated using principal component analysis (PCA) for comparison to common edible oils such as soybean, corn, coconut, and olive oil. Some tendencies of grouping are observed: butters with medium chain fatty acids (FA); butters with high oleic FA; and oils with high oleic and high linoleic FA contents. This study provided profiles that ensure Amazonian oils and butters authenticity, quality and also aids in understanding their properties and the best applications for each. Practical Applications: It is expected that this comprehensive set of data on the TAG composition of Amazonian oils and butters will help guide the use and applications of these products, providing consumers with the best benefits from a nutritional perspective. Moreover, adulterations could be more easily detected when a database is available, since the chemical composition of certified samples is investigated in this work. Ultimately, this study can encourage the sustainable production and applications of Amazonian oils and appropriate use of Amazon rain forest resources.     

Quantification of polycyclic aromatic hydrocarbons (PAHs) in the smoke from six woods and comparative study of their distribution

Polycyclic aromatic hydrocarbons (PAHs) are considered as undesirable molecules in smoke. It is important to know the smoke composition applied to meat-based products. PAH extracts of the smoke from five tropical woods were fractionated, analyzed then compared to that of beechwood, a European wood commonly used in the smoking industry of meat-based products. The identification and quantification of the aromatic molecules was carried out with gas chromatography coupled to mass spectrometry (GC/MS).     

高效液相色谱-串联质谱法分析烟草中拟除虫菊酯农药残留

建立了液相-串联质谱法(LC-MS/MS)快速测定烟草样品中5种拟除虫菊酯农药残留的分析方法.以乙腈为溶剂,对烟草样品与氟罗里硅土混合的试样采用加速溶剂萃取仪萃取,浓缩,以甲醇-0.1%醋酸铵的水溶液(体积比98∶2)为流动相,经高效液相色谱分离,以串联质谱在采用多反应监控(MRM)模式下测定.5种拟除虫菊酯农药线性关系良好,平均加标回收率在76.30%～103.64%之间,相对标准偏差为1.87%～7.48%.     

高效液相色谱-电喷雾串联质谱法测定水产品中14种喹诺酮类与磺胺类药物残留

建立了高效液相色谱-电喷雾串联质谱法测定水产品中恩诺沙星、环丙沙星、双氟沙星、沙拉沙星、氟甲喹、喹酸、磺胺嘧啶、磺胺甲唑、磺胺喹啉、磺胺甲基嘧啶、磺胺二甲氧嘧啶、磺胺二甲基嘧啶、磺胺间二甲氧嘧啶、甲氧苄胺嘧啶共14种常用喹诺酮类与磺胺类兽药的残留检测方法。样品制备后,采用1%乙酸-乙腈提取液提取,用正己烷净化处理后,采用LC/MS/MS电喷雾电离(ESI),多反应监测(MRM)正离子模式检测,外标法定量。在0～100μg/kg范围内14种兽药的线性相关系数均>0.99。在添加浓度5～50μg/kg范围内,14种药物的回收率在70.0%～110%,相对标准偏差(RSD)均在12%以内。方法的检出限为0.1～0.5μg/kg。     

Application of DNPH Derivatization with LC/MS to the Identification of Polar Carbonyl Disinfection Byproducts in Drinking Water

A qualitative method using 2,4-dinitrophenylhydrazine (DNPH) derivatization followed by analysis with liquid chromatography (LC)/negative ion-electrospray mass spectrometry (MS) was developed for analyzing and identifying highly polar aldehydes and ketones in ozonated drinking water. Using this method, aldehydes could be easily distinguished from ketones by differences in their mass spectra and chromatographic behavior. Results for many polar-substituted aldehyde and ketone standards are presented, as well as the identification of polar disinfection by-products (DBPs) in ozonated drinking water from full-scale plants and laboratory-scale ozonation of humic acid. One polar DBP identified has not been previously reported. This method could also potentially be used as a tool to identify carbonyl-containing DBPs from disinfectants other than ozone. However, the detection limits for the DNPH-LC/MS method are not as low as for the pentafluorobenzylhydroxylamine (PFBHA)-gas chromatography (GC)/MS method (LC/MS is typically not as sensitive as GC/MS). Therefore, it is not recommended that this method replace the PFBHA-GC/MS method, but be used as a supplement to enable the identification of highly polar carbonyl-containing DBPs that would not be possible by GC/MS.     

A Computational Drug Metabolite Detection Using the Stable Isotopic Mass-Shift Filtering with High Resolution Mass Spectrometry in Pioglitazone and Flurbiprofen

The identification of metabolites in drug discovery is important. At present, radioisotopes and mass spectrometry are both widely used. However, rapid and comprehensive identification is still laborious and difficult. In this study, we developed new analytical software and employed a stable isotope as a tool to identify drug metabolites using mass spectrometry. A deuterium-labeled compound and non-labeled compound were both metabolized in human liver microsomes and analyzed by liquid chromatography/time-of-flight mass spectrometry (LC-TOF-MS). We computationally aligned two different MS data sets and filtered ions having a specific mass-shift equal to masses of labeled isotopes between those data using our own software. For pioglitazone and flurbiprofen, eight and four metabolites, respectively, were identified with calculations of mass and formulas and chemical structural fragmentation analysis. With high resolution MS, the approach became more accurate. The approach detected two unexpected metabolites in pioglitazone, i.e., the hydroxypropanamide form and the aldehyde hydrolysis form, which other approaches such as metabolite-biotransformation list matching and mass defect filtering could not detect. We demonstrated that the approach using computational alignment and stable isotopic mass-shift filtering has the ability to identify drug metabolites and is useful in drug discovery.     

Atmospheric pressure chemical ionization mass spectrometry for analysis of lipids

Atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) has proven to be a very valuable technique for analysis of lipids from a variety of classes. This instrumental method readily produces useful ions with gentle fragmentation from large neutral molecules such as triacylglycerols and carotenoids, which are often difficult to analyze using other techniques. Molecules that are easily ionized, such as phospholipids, produce molecular ions and diagnostically useful fragment ions that are complementary to those produced by methods such as electrospray ionization MS with collision-induced dissociation. The simplicity and versatility of APCI-MS make it an ideal tool for use in solving hitherto very difficult analytical problems.     

Characterization of brighteners in detergents by high-performance liquid chromatography/mass spectrometry/ultraviolet/fluorescence and three-dimensional high-performance liquid chromatography

A method has been developed for the identification of unknown brighteners in detergents by a high-performance liquid chromatography (HPLC)/mass spectrometry (MS)/ultraviolet (UV)/fluorescence system with MS/MS capability. Ten brighteners from five groups—stilbene, biphenyl stilbene, pyrazoline, oxazole, and coumarin derivatives—were separated on a C₈ reverse-phase HPLC column. The UV and fluorescence detectors positively located the brightener peaks and differentiated betweentrans andcis isomers separated by the chromatographic system. Ion-spray (IS)/MS and IS/MS/MS spectra were then used to identify the structure of unknown brighteners in detergent products. An HPLC with a diode-array detector provided a quick identification check and accurate quantitative data for known brighteners, even on overlapping peaks.