LC Determination of Trace Biogenic Amines in Foods Samples with Fluorescence Detection and MS Identification

A pre-column derivatization method for the simple, sensitive determination of biogenic amines using 10-ethyl-acridine-3-sulfonyl chloride (EASC) as labeling reagent with fluorescence detection and mass spectrometry (MS) identification has been developed. After pre-column derivatization, the labeled biogenic amines were separated on a Hypersil BDS-C18 column by gradient elution. The derivatives showed an intense protonated molecular ion corresponding m/z [M + H]⁺ in positive-ion mode. The collision-induced dissociation of protonated molecular ion formed specific fragment ions at m/z 196.5, m/z 222.7, m/z 224.4 and m/z 272.5, m/z 286.2. Satisfactory linear responses were observed at the concentration range of 0.02?C10 ??mol L^?1 with coefficients of >0.9993. Detection limits obtained by the analysis of a derivatized standard containing 0.2 pmol of each biogenic amine, were from 20.22 to 109.2 fmol (at a signal-to-noise ratio of 3). The relative standard deviations of retention times and peak areas for each biogenic amine were <0.96 and 3.22%, respectively. Recoveries except for PUT were in the range of 96.7?C103.6% for chicken sausage and 95.8?C104.6% for pork sausage The established method for the determination of biogenic amines except for PUT from real samples was satisfactory.     

LC-DAD-ESI-MS Characterization of Carbohydrates Using a New Labeling Reagent

A novel labeling reagent 1-(2-naphthyl)-3-methyl-5-pyrazolone (NMP) coupling to liquid chromatography with electrospray ionization mass spectrometry for the detection of carbohydrates from the derivatized rape bee pollen samples is reported. Carbohydrates are derivatized to their bis-NMP-labeled derivatives. Derivatives showed an intense protonated molecular ion at m/z [M+H]⁺ in positive-ion detection mode. The mass-to-charge ratios of characteristic fragment ions at m/z 473.0 could be used for the accurately qualitative analysis of carbohydrates. This characteristic fragment ion is from the cleavage of C2–C3 bond in carbohydrate chain giving the specific fragment ions at m/z [MH-C _m H_2m+1O _m -H₂O]⁺ for pentose, hexose and glyceraldehydes and at m/z [MH-C _m H_2m-1O _m+1-H₂O]⁺ for alduronic acids such as galacturonic acid and glucuronic acid (m = n ? 2, n is carbon number of carbohydrate). No interferences for all aliphatic and aromatic aldehydes presented in natural environmental samples were observed due to the highly specific parent mass-to-charge ratio and the characteristic fragment ions. The method, in conjunction with a gradient elution, offered a baseline resolution of carbohydrate derivatives on a reversed-phase Hypersil ODS-2 column. The carbohydrates such as mannose, galacturonic acid, glucuronic acid, rhamnose, glucose, galactose, xylose, arabinose and fucose can successfully be detected.     

10-Ethyl-acridine-2-sulfonyl Chloride: A New Derivatization Agent for Enhancement of Atmospheric Pressure Chemical Ionization of Estrogens in Urine

The extensive metabolism and treatment of low doses of estrone (E1), estradiol (E2) and estriol (E3) in preclinical animal species necessitates a sensitive analytical method to identify or quantify the estrogens in biological matrixes. In this study, a highly sensitive and specific method based on the derivatization of E1, E2 and E3 with 10-ethyl-acridine-2-sulfonyl chloride (EASC) coupled with liquid chromatography-ion-trap mass spectrometry with APCI-MS (MRM) identification of estrogens has been developed. The EASC derivatization of E1, E2 and E3 introduces an acridine functional group into estrogen molecules. The carbonyl group in EASC core results in the formation of a phenoxide negative ion by the intramolecular keto-enol isomerization that can be accepted a [H]⁺ and readily ionized in commonly used LC mobile phases. Derivatives are sufficiently stable to be efficiently analyzed by LC-APCI-MS and show an intense protonated molecular ion at m/z [M+H]⁺ in positive-ion mode. The collision-induced dissociation of molecular ion forms a distinctive product ion at m/z 222.6, corresponding to the protonated 10-ethyl-acridine moiety. The selected reaction monitoring, based on the m/z [M+H]⁺ → m/z 222.6 transitions, is highly specific for estrogen derivatives. Therefore, the facile EASC derivatization coupling with LC-APCI-MS analysis allows the development of a highly sensitive and specific method for the identification of trace levels of estrogens in urine of root vole (Microtus oeconomus Pallas).     

Ionisation Chimique de Composés Aromatiques Nitrés

The collision induced dissociations of [MH – 30]⁺ ions observed in the chemical ionization (methane) mass spectra of some nitro aromatic compounds show that these ions are formed by reduction in the ion source with subsequent protonation and not by the previously reported losses of NO^· from the protonated molecular ions.     

Evaluation of the α‐phenylvinyl cation as a chemical ionization reagent for the differentiation of isomeric substituted phenols in an ITMS

Ion–molecule reactions between the α‐phenylvinyl cation and isomeric naturally occurring phenols were investigated using a quadruple ion trap mass spectrometer. The α‐phenylvinyl cation m/z 103, generated by chemical ionization from phenylacetylene, reacts with neutral aromatic compounds to form the characteristic species: [M + 103]⁺ adduct ions and the trans‐vinylating product ions [M + 25]⁺, which correspond to [M + 103]⁺ adduct after the loss of benzene. Isomeric differentiation of several ring‐substituted phenols was achieved by using collision‐induced dissociation of the [M + 103]⁺ adduct ions. This method also showed to be effective in the differentiation of 4‐ethylguaiacol from one of its structural isomers that displays identical EI and EI/MS/MS spectra. The effects of gas‐phase alkylation with phenylvinyl cation on the dissociation behavior were examined using mass spectrometryⁿ and labeled derivatives. Copyright © 2015 John Wiley & Sons, Ltd.     

Protonation susceptibility and fragmentation capability of functional groups in chemical ionization mass spectrometry of simple bifunctional compounds. Semi-quantitative interpretation of spectra

Positive-ion, methane-mediated chemical ionization mass spectra were measured for simple bifunctional aromatic compounds of the type m-XCH₂C₆H₄CH₂Y, where X = NH₂ and N(CH₃)₂, and Y = OH and OCH₃. Essentially only three peaks of ions, [MH]⁺, [MH – XH]⁺ and [MH – YH]⁺, have appeared for each compound. Since the two functional groups XCH₂– and YCH₂– do not interact with each other after protonation or after fragmentation, they are assumed to be protonated and to undergo fragmentations independently. The relative protonation susceptibility and fraction of fragmenting [MH]⁺ can be estimated for each functional group in these compounds. A semi-quantitative interpretation of the observed spectra is presented.     

Determination and Identification of Primary Aliphatic Amines Using 4-(1H-Phenanthro[9,10-d]Imidazol-2-yl)Benzoic Acid as Novel Pre-Column Labeling Reagent by LC with Fluorescence Detection and Atmospheric Pressure Chemical Ionization Mass Spectroscopy

4-(1H-Phenanthro[9,10-d]imidazol-2-yl)benzoic acid (PIBA), a new amine-reactive fluorescent probe was synthesized and used as a pre-column derivatizing reagent for the determination of aliphatic amines from environmetal water samples. Derivatization was successfully carried out by a condensation reaction using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride as the dehydrant. Studies on derivatization conditions indicated that the condensation reaction proceeded rapidly and smoothly in the presence of pyridine. Amines were labeled with PIBA to give the corresponding sensitively fluorescent derivatives with an excitation maximum at λ _ex 260 nm and an emission maximum at λ _em 445 nm. Identification of derivatives was carried out by online APCI–MS–MS and showed an intense protonated molecular ion corresponding m/z [M + H]⁺ in the positive ion mode. Excellent linear responses were observed with coefficients of >0.9996. Detection limits were 6.7–27 fmol (at a signal-to-noise ratio of 3). The mean intra- and inter-assay precision for all amine levels were <2.79 and 3.85%, respectively. The established method for the determination of aliphatic amines from real water was satisfactory.     

Gas Phase Decarbonylation and Cyclization Reactions of Protonated N-Methyl-N-Phenylmethacrylamide and Its Derivatives Via an Amide Claisen Rearrangement

Gas phase decarbonylation and cyclization reactions of protonated N-methyl-N-phenylmethacrylamide and its derivatives (M·H⁺) were studied by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). MS/MS experiments of M·H⁺ showed product ions were formed by loss of CO, which could only occur with an amide Claisen rearrangement. Mechanisms for the gas phase decarbonylation and cyclization reactions were proposed based on the accurate m/z measurements and MS/MS experiments with deuterated compounds. Theoretical computations showed the gas phase Claisen rearrangement was a major driving force for initiating gas phase decarbonylation and cyclization reactions of M·H⁺. Finally, the influence of different phenyl substituents on the gas phase Claisen rearrangement was evaluated. Electron-donating groups at the para-position of the phenyl moiety promoted the gas phase Claisen rearrangement to give a high abundance of fragment ions [M ? CO + H]⁺. By contrast, electron-withdrawing groups on the phenyl moiety retarded the Claisen rearrangement, but gave a fragment ion at m/z 175 by loss of neutral radicals of substituents on the phenyl, and a fragment ion at m/z 160 by further loss of a methyl radical.     

Development of a Sensitive Reagent, 1,2-Benzo-3,4-dihydrocarbazole-9-ethyl-p-toluenesulfonate, for Determination of Bile Acids in Serum by HPLC with Fluorescence Detection, and Identification by Mass Spectrometry with an APCI Source

A pre-column derivatization method with 1,2-benzo-3,4-dihydrocarbazole-9-ethyl-p-toluenesulfonate (BDETS) as labeling reagent followed by high-performance liquid chromatography with fluorescence detection has been developed for sensitive determination of bile acids (BA). Derivatives were sufficiently stable to be efficiently analyzed by high-performance liquid chromatography. The derivatives also formed an intense protonated molecular ion corresponding to m/z (M + H)⁺, and fragment ions at (MH⁺ – H₂O)⁺, (MH⁺ – 2H₂O)⁺, and (MH⁺ – 3H₂O)⁺, in positive-ion mass spectrometry with an APCI source. Collision-induced dissociation of the protonated molecular ion produced fragment products at m/z 319.1 and 246.1 corresponding to cleavage of the C-O and N-CO bonds of derivative molecules. Maximum yields close to 100% were observed when a 10 to 15-fold molar excess of the reagent was used in the presence of potassium citrate as catalyst. The derivatives fluoresced strongly, which enabled the direct injection with no significant disturbance from the main by-products from reagent degradation, for example 1,2-benzo-3,4-dihydrocarbazole-9-ethanol (BDCE-OH). The limit of detection, at a signal-to-noise ratio of 3, was 12.94–21.94 fmol. Results from validation showed the method to be highly accurate and precise (<6.4%). Excellent linear responses were observed with correlation coefficients >0.9996.     

Role of the UV absorber as a matrix in matrix‐assisted laser desorption/ionization mass spectrometric analysis of a mixture of a UV absorber and a stabilizer

A mixture of a UV absorber (Tinuvin 234 or Tinuvin 329) and a UV stabilizer (Tinuvin 770) was analyzed using matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) without any matrix. Fragmentation patterns of the UV absorbers and stabilizer were also investigated. The mass spectra showed the [M+H]⁺ ions and some fragment ions. Tinuvin 234, Tinuvin 329, and Tinuvin 770 generated three (m/z 119, 370, 432), one (m/z 252), and two (m/z 124 and 140) fragment ions, repectively. These fragment ions can be used to identify the chemical structures of the UV absorbers and stabilizer. Since the UV absorber performed a role as the matrix, the ion abundance of the UV stabilizer was enhanced by mixing with the UV absorber. When organic materials extracted from polypropylene (PP) containing the UV absorber and stabilizer were directly analyzed using MALDI‐MS without any matrix, the protonated molecule of the UV stabilizer was detected in abundance but the product ions of the UV absorber were not observed. When 2,5‐dihydroxybenzoic acid was used as a matrix, the protonated molecule of the UV absorber was observed. Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of Free Fatty Acids in Tibet Folk Medicine Potentilla anserina L. Using a New Labeling Reagent by LC with Fluorescence Detection and Identification with Online Atmospheric Chemical Ionization-MS Identification

A sensitive method for the determination of free fatty acids using 1,2-benzo-carbazole-9-ethyl-p-toluenesulfonate (BCETS) as tagging reagent with fluorescence detection has been developed. BCETS could easily and quickly label fatty acids in the presence of the K₂CO₃ catalyst at 80 °C for 30 min in N,N-dimethylformamide solvent. In this study, fatty acids from the extracted Potentilla anserina L. plant sample were sensitively determined. The corresponding derivatives were separated on a reversed-phase Eclipse XDB-C₈ column by LC in conjunction with gradient elution. The identification was carried out by post-column APCI-MS in positive-ion detection mode. BCETS-fatty acid derivatives gave an intense molecular ion peak at m/z [M+H]⁺, the collision-induced dissociation spectra of m/z [M+H]⁺ produced the specific fragment ions at m/z [M′+CH₂CH₂]⁺, m/z 216.6 and m/z [MH?H₂O]⁺ (here, M′: corresponding molecular mass of the fatty acids). The fluorescence excitation and emission wavelengths of the derivatives were at λ _ex 279 nm and λ _em 380 nm, respectively. Linear correlation coefficients for all fatty acid derivatives are more than 0.9994. Detection limits, at a signal-to-noise ratio of 3:1, are 10.79–34.19 fmol for the labeled fatty acids.     

Rapid and Sensitive LC−MS–MS Method for the Determination of Sarpogrelate in Human Plasma

A rapid and sensitive liquid chromatographic–tandem mass spectrometric method has been developed and validated for the estimation of sarpogrelate in human plasma. Sarpogrelate was extracted from human plasma by solid-phase extraction. Temocapril was used as the internal standard. Heated electron spray ionization mass spectrometry was performed on a TSQ Quantum Ultra MS system. The LC column was a Hypurity C₁₈ and the mobile phase was 2 mM ammonium formate (pH 3.00 ± 0.05):acetonitrile (30:70 v/v). A flow rate of 0.250 mL min^?1 was used. The quantitative analyses were carried out in the positive ion and full scan mode over the mass range m/z 60–500. The capillary, vaporiser temperatures were 325 and 200 °C respectively. The sheath gas pressure, spray voltage, collision energy and tube lense were 40, 3,500 V, 19 V, 198 V, respectively, and the mass spectra of the drugs were recorded by total ion monitoring. Retention times and characteristic mass fragments were recorded and the chosen diagnostic mass fragments were monitored in the mass chromatography mode. Signal intensities of each of the mass fragments: m/z 477 [M + H]⁺ for temocapril, m/z 430 [M + H]⁺ for sarpogrelate, were used for quantification. The calibration curves (the ratio between the peak areas as signal intensities of the drug analyzed and that of the internal standard (temocapril: m/z 477 [M + H]⁺) vs. the concentration of drug) exhibited linearity over the concentration range 5.00–2,500.00 ng mL^?1 human plasma. The recovery and the accuracy were calculated by comparing the peak areas as the signal intensities of each mass fragment for the drug in spiked samples after solid-phase extraction from human plasma to the peak area as the signal intensity of the mass fragment of internal standard sample. The method involves a rapid solid phase extraction from plasma, simple isocratic chromatography conditions and mass spectrometric detection that enables detection up to picogram levels with a total run time of 3.0 min only. The method was validated over the range of 5.0–2,500.0 ng mL^?1. The absolute recoveries for sarpogrelate (93.72%) and IS (91.42%) achieved from spiked plasma samples were consistent and reproducible.     

A sensitive fluorescence reagent for the determination of aldehydes from alcoholic beverage using high-performance liquid chromatography with fluorescence detection and mass spectrometric identification

A pre-column derivatization method for the sensitive determination of aldehydes using the tagging reagent 2-[2-(7H-dibenzo[a,g] carbazol-7-yl)-ethoxy] ethyl carbonylhydrazine (DBCEEC) followed by high-performance liquid chromatography with fluorescence detection and APCI-MS identification has been developed. The chromophore of fluoren-9-methoxy-carbonylhydrazine (Fmoc-hydrazine) reagent was replaced by 2-[2-(7H-dibenzo[a,g] carbazol-7-yl)-ethoxy] ethyl functional group, which resulted in a sensitive fluorescence tagging reagent DBCEEC. DBCEEC could easily and quickly labeled aldehydes. The maximum excitation (300 nm) and emission (400 nm) wavelengths did not essentially change for all the aldehyde derivatives. Derivatives were sufficiently stable to be efficiently analyzed by high-performance liquid chromatography. The derivatives showed an intense protonated molecular ion corresponding m/z [M + (CH₂)_n]⁺ in positive-ion mode (M: molecular weight of DBCEEC, n: corresponding aldehyde carbon atom numbers). The collision-induced dissociation of protonated molecular ion formed fragment ions at m/z 294.6, m/z 338.6 and m/z 356.5. Studies on derivatization demonstrated excellent derivative yields in the presence of trichloroacetic acid (TCA) catalyst. Maximal yields close to 100% were observed with a 10 to 15-fold molar reagent excess. Separation of the derivatized aldehydes had been optimized on ZORBAX Eclipse XDB-C₈ column with aqueous acetonitrile as mobile phase in conjunction with a binary gradient elution. Excellent linear responses were observed at the concentration range of 0.01-10 nmol mL⁻¹ with coefficients of >0.9991. Detection limits obtained by the analysis of a derivatized standard containing 0.01 nmol mL⁻¹ of each aldehyde, were from 0.2 to 1.78 nmol L⁻¹ (at a signal-to-noise ratio of 3).     

Microbial Transformation of Curcumin to Its Derivatives with a Novel <Emphasis Type="Italic">Pichia kudriavzevii</Emphasis> ZJPH0802 Strain

Curcumin, a polyphenolic compound, has shown a wide range of pharmacological activities and has been widely used as a food additive. However, the clinical use of curcumin is limited to some extent because of its poor water solubility and low bioavailability. To overcome these problems, many approaches have been attempted and structural modification of curcumin by microbial transformation has been proven to be an alternative. In this study, we isolated a novel yeast strain Pichia kudriavzevii ZJPH0802 from a soil sample, which is capable of converting curcumin to its derivatives. The transformed products by this strain were evaluated by HPLC, (+) electrospray ionization (ESI)-MSⁿ, and ¹H nuclear magnetic resonance methods. Compared with controls, two new peaks of the transformed broth appeared at retention times of 26 min (I) and 62 min (II) by HPLC analysis. The two transformed products were then further identified by (+) ESI-MSⁿ. The spectrum showed that compound I had an accurate [M+H+NH₃]⁺ ion at m/z 392, [M+H]⁺ ion at m/z 375, [M+H–H₂O]⁺ ion at m/z 357, and (+) ESI-MS³ spectrum showed that ion at m/z 357 could further form fragment ions at m/z 339, 177, and 163; compound II had an accurate [M+H]⁺ ion at m/z 373, [M+H–H₂O]⁺ ion at m/z 355, and (+) ESI-MS³ spectrum showed that ion at m/z 355 could further form fragment ions at m/z 219, 179, 177, 163, and 137. These two transformed products thereby were confirmed as hexahydrocurcumin (I) and tetrahydrocurcumin (II).     

Structural determination by atmospheric pressure photoionization tandem mass spectrometry of some compounds isolated from the SARA fractions obtained from bitumen

We have identified compounds obtained from the SARA fractions of bitumen by using atmospheric pressure photoionization mass spectrometry and low‐energy collision tandem mass spectrometric analyses with a QqToF‐MS/MS hybrid instrument. The identified compounds were isolated from the maltene saturated oil and the aromatic fractions of the SARA components of a bitumen. The QqToF instrument had sufficient mass resolution to provide accurate molecular weight information and to enhance the tandem mass spectrometry results. The APPI‐QqToF‐MS analysis of the separated compounds showed a series of protonated molecules [M + H]⁺ and molecular ions [M]^+? of the same mass but having different chemical structures, in the maltene saturated oil and the aromatic SARA fractions. These isobaric ions were a molecular ion [M₂]^+? at m/z 418.2787 and a protonated molecule [M₅ + H]⁺ at m/z 287.1625 in the saturated oil fraction, and molecular ions [M₆]^+? at m/z 418.1584 and [M₇]^+? at m/z 287.1285 in the aromatic fraction. The identification of this series of chemical compounds was achieved by performing CID‐MS/MS analyses of the molecular ions [M]^+? ([M₁]^+? at m/z 446. 2980, [M₂]^+? at m/z 418.2787, [M₃]^+? at m/z 360.3350 and [M₄]^+? at m/z 346.2095) in the saturated oil fraction and of the [M₅ + H]⁺ ion at m/z 287.1625 also in the saturated oil fraction. The observed CID‐MS/MS fragmentation differences were explained by proposed different breakdown processes of the precursor ions. The presented tandem mass spectrometric study shows the capability of MS/MS experiments to differentiate between different classes of chemical compounds of the SARA components of bitumen and to explain the reasons for the observed mass spectrometric differences. However, greater mass resolution than that provided by the QqToF‐MS/MS instrument would be required for the analysis of the asphaltene fraction of bitumen. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterisation and quantification of liposome-type nanoparticles in a beverage matrix using hydrodynamic chromatography and MALDI–TOF mass spectrometry

This paper describes the characterisation of liposome-type nanoparticles (NPs) dispersed in a beverage matrix. Characterisation is based on a two-step procedure: first, liposomes are separated on the basis of size in the nanometre range by use of hydrodynamic chromatography (HDC); second, chemical characterisation is performed by use of MALDI–TOF mass spectrometry (MS). Characterisation of three types of Coatsome liposome, a commercially available type of empty liposome, was investigated. All three liposome types, Coatsome A?=?anionic, N?=?neutral, and C?=?cationic, gave single peaks in HDC, reflecting diameters of 153, 187, and 205 nm, respectively. Subsequent MALDI–TOF MS in positive mode furnished major signals at m/z?=?734.5 ([M?+?H]⁺ adduct) and m/z?=?756.6 ([M?+?Na]⁺ adduct) of l-(α)-dipalmitoylphosphatidylcholine (DPPC) monomer and dimeric adducts at m/z?=?1468.1 and m/z?=?1490.1, respectively. MALDI–TOF MS in negative mode gave a signal at m/z?=?721.3 ([M???H]^? adduct) of l-(α)-dipalmitoylphosphatidylglycerol (DPPG), except for Coatsome C which lacks this phospholipid. After HDC separation of Coatsome A NPs the major DPPC and DPPG signals can be detected in the expected fractions by use of MALDI–TOF MS in positive and negative modes, respectively. Validation of the analytical strategy revealed linearity (R ²?>?0.99), repeatability (relative standard deviation <10 %), and reproducibility (relative standard deviation between days <10 %) were good, recovery was 61?±?5 %, and the limit of quantification was 1 mg?mL^?1 in this matrix. With 4 mg Coatsome A mL^?1 20 out of 20 samples furnished the 734.5 and 756.6 signals typical of DPPC in MALDI–TOF MS characterisation.     

Differentiation of lisinopril and its RSS diastereomer by liquid chromatography combined with collision‐induced dissociation mass spectrometry

A simple and sensitive liquid chromatography tandem multiple‐stage mass spectrometry (HPLC/MS/MS) method suitable for bulk lisinopril analysis was developed, by which lisinopril and its RSS isomer were separated and differentiated. In the collision‐induced dissociation (CID) mass spectra of the [M + H]⁺ ions, the abundance of the fragment ion of m/z 246 for lisinopril was about two times higher than the ion of m/z 245; however, the former fragment ion was noted to be a little lower than the latter for RSS isomer at all collision energies. In the CID mass spectra of the [M + Li]⁺ ion, the abundance of the rearrangement ion of m/z 315 for the RSS isomer was about three times higher than that for lisinopril. Furthermore, the difference was supported by the results of energy‐resolved mass spectrometry (ERMS) in the test range of collision energies. Similar differences were also observed between the CID mass spectra of lisinopril and RSS isomer methylester, which indicated that the RSS isomer could be rapidly characterized by the CID mass spectra of both the protonated and lithium adduct ion. Elemental compositions of all the ions were confirmed by Fourier Transform ion cyclotron resonance ESI mass spectrometry (FT‐ICR‐ESI/MS). In addition, theoretical computations were carried out to support the experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Use of liquid chromatography/tandem mass spectrometry and online databases for identification of phosphocholines and lysophosphatidylcholines in human red blood cells

In this work a systematic strategy integrating liquid chromatography/tandem mass spectrometry (LC/MS/MS) and online databases was developed to identify phosphocholines (PC) and lysophosphatidylcholines (LPC) in human red blood cells (RBCs). First of all, the neutral loss scan of 59 and the precursor ion scan of m/z 184 were performed to find out the possible lipids with phosphocholine head‐group structure in RBCs. The acquired [M+H]⁺ and [M+Na]⁺ adduct ions were then identified online using the Human Metabolome Database (HMDB) and the LIPID MAPS, which were then further confirmed by their MS/MS fragmentation. Based on the comparison of chemical structures of the detected PC and LPC with their corresponding MS/MS fragmentation pathways, several new diagnostic fragments or fragmentation pathway were found. These include, (1) the neutral losses of 183 could be used as a diagnostic fragmentation to discriminate PC and LPC; (2) product ions at m/z 104 could be used to distinguish LPC and their sn‐2 isomers; (3) fragment ions at m/z 184 are characteristic fragmentation that could be used for discrimination of sodiated ions [M+Na]⁺ and protonated ions [M+H]⁺, especially for co‐eluted PC or LPC with a molecular weight difference of 22. The structures of the above‐mentioned fragment ions were confirmed by quadrupole time‐of‐flight (Q‐TOF) MS. Furthermore, a PC and LPC focused LC/MS semi‐quantification approach was also developed and validated. This approach could be useful for future lipidomic study. Copyright © 2009 John Wiley & Sons, Ltd.     

Mass spectrometric monitoring of oxidation of aliphatic C6–C8 hydrocarbons and ethanol in low pressure oxygen and air plasmas

Experimental and theoretical studies on the oxidation of saturated hydrocarbons (n‐hexane, cyclohexane, n‐heptane, n‐octane and isooctane) and ethanol in 28 Torr O₂ or air plasma generated by a hollow cathode discharge ion source were made. Ions corresponding to [M + 15]⁺ and [M + 13]⁺ in addition to [M ? H]⁺ and [M ? 3H]⁺ were detected as major ions where M is the sample molecule. The ions [M + 15]⁺ and [M + 13]⁺ were assigned as oxidation products, [M ? H + O]⁺ and [M ? 3H + O]⁺, respectively. By the tandem mass spectrometry analysis of [M ? H + O]⁺ and [M ? 3H + O]⁺, H₂O, olefins (and/or cycloalkanes) and oxygen‐containing compounds were eliminated from these ions. Ozone as one of the terminal products in the O₂ plasma was postulated as the oxidizing reagent. As an example, the reactions of C₆H₁₄^+? with O₂ and of C₆H₁₃⁺ (CH₃CH₂CH⁺CH₂CH₂CH₃) with ozone were examined by density functional theory calculations. Nucleophilic interaction of ozone with C₆H₁₃⁺ leads to the formation of protonated ketone, CH₃CH₂C(=OH⁺)CH₂CH₂CH₃. In air plasma, [M ? H + O]⁺ became predominant over carbocations, [M ? H]⁺ and [M ? 3H]⁺. For ethanol, the protonated acetic acid CH₃C(OH)₂⁺ (m/z 61.03) was formed as the oxidation product. The peaks at m/z 75.04 and 75.08 are assigned as protonated ethyl formate and protonated diethyl ether, respectively, and that at m/z 89.06 as protonated ethyl acetate. Copyright © 2016 John Wiley & Sons, Ltd.     

Chemical ionization and electron impact mass spectra of thiosulfinates,thiosulfonates and sulfinyl sulfones

The chemical ionization and electron impact mass spectra of some thiosulfinates, thiosulfonates and sulfinyl sulfones have been studied. The electron impact mass spectra of four of the six thiosulfonates show molecular ions of less than 1%. Inconclusive evidence was obtained for sulfenyl sulfinate type intermediates in the electron impact spectra of thiosulfonates. The electron impact spectra of thiosulfonates were similar to those of thiosulfonates. The chemical ionization (isobutane) mass spectra of thiosulfinates and thiosulfonates generally show protonated molecular ions [MH]⁺ as base peaks and [MH+1]⁺ and [MH+2]⁺ peaks.