Identification of Fe‐polycarboxylic complexes by electrospray ionization mass spectrometry and reduction of interferences by ion chromatography/inductively coupled plasma mass spectrometry with an octopole reaction system

Stable complexes are required during the ion chromatographic (IC) separation of Fe‐polycarboxylic acid complexes. Electrospray ionization mass spectrometry (ESI‐MS) was used to identify 1:1 stoichiometric complexes of Fe[HEDTA], Fe[EDTA]^1? and Fe[DTPA]^2?, and the spectra showed that these Fe complexes were stable in solution. Furthermore, inductively coupled plasma mass spectrometry (ICP‐MS) using an octopole reaction system (ORS) reduced polyatomic ion ⁴⁰Ar¹⁶O⁺ interference in the detection of ⁵⁶Fe via the addition of either H₂ or He to the ORS, with He at a flow rate 3.5 mL min^?1 being the optimum collision gas. Finally, IC/ICP‐MS was used for the separation and detection of Fe complexes with an eluent containing 30 mM (NH₄)₂HPO₄ at pH 8.0, but only Fe[HEDTA], Fe[EDTA]^1? and Fe[DTPA]^2? were observed within 10 min with reasonable resolution. Detection limits in the range of 10–13 µg L^?1 were achieved using He as the collision gas. The proposed method was used for the determination of Fe species in soil solutions. Copyright © 2010 John Wiley & Sons, Ltd.     

Confirmation of lead aminocarboxylic complex formation using electrospray ionization mass spectrometry and speciation by anion-exchange chromatography coupled with ICP-MS

Inductively coupled plasma mass spectrometry (ICP-MS) and electrospray ionization mass spectrometry (ESI-MS) were used as complementary techniques to provide element and molecular information for aminocarboxylic lead species including [Pb(NTA)]¹⁻, [Pb(HEDTA)]¹⁻, [Pb(EDTA)]²⁻ and [Pb(DTPA)]³⁻. ESI-MS was used to initially confirm the formation of lead aminocarboxylic complexes in solution and subsequently anion-change chromatography coupled with ICP-MS was used to speciate these complexes using a mobile phase containing 30 mM NH₄H₂PO₄ at pH of 8.0. However, [Pb(NTA)]¹⁻ was not observed during chromatographic separation due to its poor stability. The species [Pb(HEDTA)]¹⁻, [Pb(EDTA)]²⁻ and [Pb(DTPA)]³⁻ were separated within 15 min with reasonable resolution and detection limits ranging from 0.05 to 0.2 μg L⁻¹ with simple direct injection of sample. The proposed method was used to speciate aminocarboxylic lead complexes in soil solution.     

Fragmentation of deprotonated cyclic dipeptides by electrospray ionization mass spectrometry

The fragmentation pathways of deprotonated cyclic dipeptides have been studied by electrospray ionization multi‐stage mass spectrometry (ESI‐MSⁿ) in negative mode. The results showed that the fragmentation pathways of deprotonated cyclic dipeptides depended significantly on the different substituents, the side chains of amino acid residues at the diketopiperazine ring. In the spectra of deprotonated cyclic dipeptides, the ion [M? H? substituent radical]^? was firstly observed in the ESI mode. The characteristic fragment ions [M? H? substituent radical]^? and [M? H? (substituent? H)]^? could be used as the symbols of particular cyclic dipeptides. The hydrogen/deuterium (H/D) exchange experiment, the high‐resolution mass spectrometry (Q‐TOF) and theoretical calculations were used to rationalize the proposed fragmentation pathways and to verify the differences between the fragmentation pathways. The relative Gibbs free energies (ΔG) of the product ions and possible fragmentation pathways were estimated using the B3LYP/6–31++G(d, p) model. The results have some potential applications in the structural elucidation and interpretation of the mass spectra of homologous compounds and will enrich the gas‐phase ESI‐MS ion chemistry of cyclic dipeptides. Copyright © 2009 John Wiley & Sons, Ltd.     

Studies of gas-phase reactions of cationic iron complexes of 2-pyrimidinyloxy-N-arylbenzylamines by electrospray ionization tandem mass spectrometry

Electrospray ionization triple quadrupole mass spectrometry (ESI‐TSQ‐MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICR‐MS) were used to investigate the interesting gas‐phase reactions of the cationic iron (Fe) complexes of 2‐pyrimidinyloxy‐N‐arylbenzylamines (1–6), which are generated by ESI when mixing their methanolic solutions. Further studies of these Fe complexes by collision‐induced dissociation (CID) show that Fe(III) complexes undergo an interesting gas‐phase single electron transfer (SET) reaction to give 1^?+–6^?+,with loss of neutral FeCl₂, whereas Fe(II) can catalyze gas‐phase Smiles rearrangement reactions of compounds 1–6. By using different Fe(II)X₂ salts (X = Cl or Br) with a set of reactants, the role of the counterion (X^?) and the structure effect of the reactants on Fe(II)‐catalyzed gas‐phase Smiles rearrangement reactions are studied. Evidence obtained from by TSQ‐MS and FTICR‐MS experiments, hydrogen/deuterium (H/D) exchange experiments and theoretical computations supported some unique gas‐phase chemistries initiated by introduction of Fe(II) into 1. Importantly, by comparing the distinct gas‐phase reaction results of the cationic Fe(III) complexes with those of Fe(II) complexes, the charge state effects of iron on the gas‐phase chemistries of Fe complexes are revealed. Copyright © 2010 John Wiley & Sons, Ltd.     

Speciation of chromium in waste water using ion chromatography inductively coupled plasma mass spectrometry

Ion chromatography (IC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) was systematically investigated for determining the speciation of chromium in environmental samples. Firstly, the stability of complexes formed by Cr(III) with various aminopolycarboxylic acids was studied by electrospray ionization mass spectrometry (ESI-MS). The results showed that [Cr(EDTA)]⁻ was stable in solution. Secondly, various mobile phases were examined to separate Cl⁻ from chromium species by IC to avoid Cl⁻ interference. The separation of [Cr(EDTA)]⁻ and Cr(VI) was achieved on a new anion-exchange column (G3154A/102) using a mobile phase containing 20 mM NH₄NO₃ and 10 mM NH₄H₂PO₄ at pH 7.0 without Cl⁻ interference. Detection limits for chromium species were below 0.2 μg/L with a direct injection of sample and without prior removal of interferences from the matrix. Finally, the proposed method was used for the determination of chromium species in contaminated waters.     

A novel method for determination of inorganic oxyanions by electrospray ionization mass spectrometry using dehydration reactions

Novel methods for the determination of inorganic oxyanions by electrospray (ES) ionization mass spectrometry have been developed using dehydration reactions between oxyanions and carboxylic acids at the ES interface. Twelve oxyanions (VO₃^?, CrO₄^2?, MoO₄^2?, WO₄^2?, BO₃^3?, SiO₃^2?, SiO₄^4?, AsO₄^4?, AsO₂^?, SeO₄^2?, SeO₃^2? and NO₂^?), out of 16 tested, reacted with at least one of four aminopolycarboxylic acids, i.e. iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetic acid and triethylenetetramine‐N,N,N′,N″,N′″,N′″‐hexaacetic acid, at the ES interface to produce the dehydration products that gave intense mass ion responses, sufficient for trace analysis. As examples, trace determinations of Cr^VI and silica in water samples were achieved after online ion exchange chromatography, where the dehydration product of CrO₄^2? and NTA (m/z 290) and that of SiO₄^4? and IDA (m/z 192) were measured. The limits of detection of the respective methods were 17 nM (0.83 ng Cr/ml) for Cr^VI and 0.17 μM (4.8 ng Si/mL) for SiO₄^4?. Copyright © 2016 John Wiley & Sons, Ltd.     

Capillary electrophoresis/mass spectrometry for the separation and characterization of bovine Cu,Zn‐superoxide dismutase

The native form of Cu,Zn‐superoxide dismutase (SOD‐1) is a homodimer that coordinates one Cu²⁺ and one Zn²⁺ per monomer. Cu²⁺ and Zn²⁺ ions play crucial roles in enzyme activity and structural stability, respectively. In addition, dimer formation is essential for SOD‐1 functionality, and in humans several SOD‐1 mutant isoforms have been associated with certain types of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder. In this paper we used capillary electrophoresis and mass spectrometry to study the different structures of bovine SOD‐1. The metal ions of the native enzyme (Cu₂,Zn₂‐dimer SOD‐1) were released in acidic medium in order to obtain apo‐SOD‐1, which is a monomer. Both substances were analyzed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) and capillary electrophoresis with ultraviolet and electrospray ionization mass spectrometry detection (CE/UV and CE/ESI‐MS, respectively). With MALDI‐TOF‐MS, using matrices of sinapinic acid (SA) or 2,5‐dihydroxybenzoic acid (DHB) with or without trifluoroacetic acid (TFA), similar mass spectra were obtained for the metalated and non‐metalated samples. In both cases, an average molecular mass corresponding to the apo‐monomer SOD‐1 was calculated. This finding indicated that the metals were released from the Cu₂,Zn₂‐dimer SOD‐1 during sample preparation or ionization. For CE/UV and CE/ESI‐MS, two background electrolytes (BGEs) potentially compatible with ESI‐MS detection were used, namely 1 M of acetic acid (pH 2.3) and 10 mM of ammonium acetate (pH 7.3). Using a sheath liquid of 2‐propanol/water (60:40 v/v), with or without 0.1% v/v of formic acid, CE/ESI‐MS sensitivity was enhanced when the acidic BGE and the acidic sheath liquid were used. However, the electrophoretic profiles and the mass spectra obtained suggested that the metals of Cu₂,Zn₂‐dimer SOD‐1 were released, which generated the apo‐monomer during the electrophoretic separation. The neutral BGE provided enhanced conditions for the detection of the native enzyme. The differences between the mass spectra obtained for the Cu₂,Zn₂‐dimer and the apo‐monomer forms were significant and the presence of formic acid in the sheath liquid affected only sensitivity. Our results highlight the importance of selecting appropriate non‐denaturing separation and detection conditions to obtain reliable structural information about non‐covalent protein complexes by CE/ESI‐MS. Copyright © 2010 John Wiley & Sons, Ltd.     

Improved characterization of tomato polyphenols using liquid chromatography/electrospray ionization linear ion trap quadrupole Orbitrap mass spectrometry and liquid chromatography/electrospray ionization tandem mass spectrometry

Tomato (Lycopersicon esculentum Mill.) is the second most important fruit crop worldwide. Tomatoes are a key component in the Mediterranean diet, which is strongly associated with a reduced risk of chronic degenerative diseases. In this work, we use a combination of mass spectrometry (MS) techniques with negative ion detection, liquid chromatography/electrospray ionization linear ion trap quadrupole‐Orbitrap‐mass spectrometry (LC/ESI‐LTQ‐Orbitrap‐MS) and liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS) on a triple quadrupole, for the identification of the constituents of tomato samples. First, we tested for the presence of polyphenolic compounds through generic MS/MS experiments such as neutral loss and precursor ion scans on the triple quadrupole system. Confirmation of the compounds previously identified was accomplished by injection into the high‐resolution system (LTQ‐Orbitrap) using accurate mass measurements in MS, MS² and MS³ modes. In this way, 38 compounds were identified in tomato samples with very good mass accuracy (<2 mDa), three of them, as far as we know, not previously reported in tomato samples. Copyright © 2010 John Wiley & Sons, Ltd.     

Ion chromatography–inductively coupled plasma mass spectrometry determination of arsenic species in marine samples

Arsenic speciation analysis in marine samples was performed using ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP‐MS) detection. The separation of eight arsenic species, viz. arsenite, monomethyl arsonic acid, dimethylarsinic acid, arsenate, arsenobetaine, tetramethylarsine oxide, arsenocholine and tetramethylarsonium ion was achieved on a Dionex AS4A (weaker anion exchange column) by using a nitric acid pH gradient eluent (pH 3.3 to 1.3). The entire separation was accomplished in 12 min. The detection limits for the eight arsenic species by IC–ICP‐MS were in the range 0.03–1.6 µ g l^?1, based on 3σ of the blank response (n = 6). The repeatability and day‐to‐day reproducibility were calculated to be less than 10% (residual standard deviation) for all eight species. The method was validated by analyzing a certified reference material (DORM‐2, dogfish muscle) and then successfully applied to several marine samples, e.g. oyster, fish muscle, shrimp and marine algae. The low power microwave digestion was employed for the extraction of arsenic from seafood products. Copyright © 2004 John Wiley & Sons, Ltd.     

甾体磷酰胺类缀合物在电喷雾质谱中的裂解特征

Novel steroidal phosphoramidate conjugates of 3'-azido-2',3'-dideoxythymidine(AZT)and amino acid esterswere synthesized and determined by positive and negative ion electrospray ionization mass spectrometry.The MSfragmentation behaviors of the steroidal phosphoramidate conjugates have been investigated in conjunction withtandem mass spectrometry of ESI-MS/MS.There were three characteristic fragment ions in the positive ion ESImass spectra,which were the Na adduct ions with loss of steroidal moiety,amino acid ester moiety from pseudomolecular ion(M Na)~ ,and the phosphoamino acid methyl ester Na adduct ion by α-cleavage of the phosphora-midate respectively.The main fragment ions in negative ion ESI mass spectra were the ion(M-HN_3)~-,the ion(M-AZT-H)~-,and the ion(M-steroidal moiety-H)~- besides the pseudo molecular ion(M-H)~-.Thefragmentation patterns did not depend on the attached amino acid ester moiety.     

Tetrakis(diethyl‐phosphonat)‐, Tetrakis(ethyl‐phenylphosphinat)‐ und Tetrakis(diphenylphosphin‐oxid)‐substituierte Phthalocyanine

Tetrakis(diethyl phosphonate), Tetrakis(ethyl phenylphosphinate)‐, and Tetrakis(diphenylphosphine oxide)‐Substituted Phthalocyanines The title compounds 7, 9 , and 11 are obtained by tetramerization of diethyl (3,4‐dicyanophenyl)phosphonate ( 5 ), ethyl (3,4‐dicyanophenyl)phenylphosphinate ( 8 ), and 4‐(diphenylphosphinyl)benzene‐1,2‐dicarbonitrile ( 10 ). The ³¹P‐NMR spectra of the phthalocyanines 7, 9 , and 11 and of their metal complexes present five to eight signals confirming the formation of four constitutional isomers with the expected C_4h, D_2h, C_2v, and C_s symmetry. In the FAB‐MS of the Zn, Cu, and Ni complexes of 7 and 9 , the peaks of dimeric phthalocyanines are observed. By gel‐permeation chromatography, the monomeric complex [Ni( 7 )] and a dimer [Ni( 7 )]₂ can be separated. These dimers differ from the known phthalocyanine dimers, i.e., possibly the P(O)(OEt)₂ and P(O)(Ph)(OEt) substituents in 7 and 9 are involved in complexation. The free phosphonic acid complex [Zn( 12 )] and [Cu( 12 )] are H₂O‐soluble. In the FAB‐MS of [Zn( 12 )], only the peaks of the dimer are present; the ESI‐MS confirms the existence of the dimer and the metal‐free dimer. In the UV/VIS spectrum of [Zn( 12 )], the hypsochromic shift characteristic for the known type of dimers from 660–700 nm to 620–640 nm is observed. As in the FAB‐MS of [Zn( 12 )], the free phosphinic acid complex [Zn( 13 )] shows only the monomer, an ESI‐MS cannot be obtained for solubility problems. The UV/VIS spectrum of [Zn( 13 )] demonstrates the existence of the monomer as well as of the dimer.     

Differentiation of isomeric dinitrotoluenes and aminodinitrotoluenes using electrospray high resolution mass spectrometry

Explosive detection and identification play an important role in the environmental and forensic sciences. However, accurate identification of isomeric compounds remains a challenging task for current analytical methods. The combination of electrospray multistage mass spectrometry (ESI‐MSⁿ) and high resolution mass spectrometry (HRMS) is a powerful tool for the structure characterization of isomeric compounds. We show herein that resonant ion activation performed in a linear quadrupole ion trap allows the differentiation of dinitrotoluene isomers as well as aminodinitrotoluene isomers. The explosive‐related compounds: 2,4‐dinitrotoluene (2,4‐DNT), 2,6‐dinitrotoluene (2,6‐DNT), 2‐amino‐4,6‐dinitrotoluene (2A‐4,6‐DNT) and 4‐amino‐2,6‐dinitrotoluene (4A‐2,6‐DNT) were analyzed by ESI‐MS in the negative ion mode; they produced mainly deprotonated molecules [M ? H]^?. Subsequent low resolution MSⁿ experiments provided support for fragment ion assignments and determination of consecutive dissociation pathways. Resonant activation of deprotonated dinitrotoluene isomers gave different fragment ions according to the position of the nitro and amino groups on the toluene backbone. Fragment ion identification was bolstered by accurate mass measurements performed using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR/MS). Notably, unexpected results were found from accurate mass measurements performed at high resolution for 2,6‐DNT where a 30‐Da loss was observed that corresponds to CH₂O departure instead of the expected isobaric NO^? loss. Moreover, 2,4‐DNT showed a diagnostic fragment ion at m/z 116, allowing the unambiguous distinction between 2,4‐ and 2,6‐DNT isomers. Here, CH₂O loss is hindered by the presence of an amino group in both 2A‐4,6‐DNT and 4A‐2,6‐DNT isomers, but nevertheless, these isomers showed significant differences in their fragmentation sequences, thus allowing their differentiation. DFT calculations were also performed to support experimental observations. Copyright © 2014 John Wiley & Sons, Ltd.     

An experimental and computational investigation on the fragmentation behavior of enaminones in electrospray ionization mass spectrometry

The dissociation pathways of protonated enaminones with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) in positive ion mode. In mass spectrometry of the enaminones, Ar? CO? CH?CH? N(CH₃)₂, the proton transfers from the thermodynamically favored site at the carbonyl oxygen to the dissociative protonation site at ipso‐position of the phenyl ring or the double bond carbon atom adjacent to the carbonyl leading to the loss of a benzene or elimination of C₄H₉N, respectively. And the hydrogen? deuterium (H/D) exchange between the added proton and the proton of the phenyl ring via a 1,4‐H shift followed by hydrogen ring‐walk was witnessed by the D‐labeling experiments. The elemental compositions of all the ions were confirmed by ultrahigh resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR‐MS/MS). The enaminones studied here were para‐monosubstituted on the phenyl ring and the electron‐donating groups were in favor of losing the benzene, whereas the electron‐attracting groups strongly favored the competing proton transfer reaction leading to the loss of C₄H₉N to form a benzoyl cation, Ar‐CO⁺. The abundance ratios of the two competitive product ions were relatively well‐correlated with the σ_p⁺ substituent constants. The mechanisms of these reactions were further investigated by density functional theory (DFT) calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of alkaloids binding to the parallel quadruplex structure [d(TGGGGT)]4 by electrospray ionization mass spectrometry

In this study, electrospray ionization mass spectrometry (ESI‐MS) was used to investigate the binding interaction of six alkaloids with parallel intermolecular G‐quadruplex [d(TGGGGT)]₄, and five alkaloids including berberine, jatrorrhizine, palmatine, tetrandrine, and fangchinoline showed complexation with the target DNA. Relative binding affinities were estimated on the basis of mass spectrometric data. The slight differences in chemical structures of berberine, jatrorrhizine, and palmatine had little influence on their binding affinities to [d(TGGGGT)]₄. Tetrandrine and fangchinoline selectively bound to [d(TGGGGT)]₄ versus duplex DNA. Collision‐induced dissociation (CID) experiments showed that the complexes with berberine, jatrorrhizine, and palmatine dissociated via strand separation and ligand retaining in the strand while the complexes with tetrandrine and fangchinoline were dissociated via ligand elimination. A comparison of dissociation patterns in CID experiments of complexes with the alkaloids to those with the traditional G‐quadruplex DNA binders suggested an end‐stacking binding mode for tetrandrine and fangchinoline and an intercalation binding mode for berberine, jatrorrhizine, and palmatine to the target DNA. The current work not only provides deep insight into alkaloid/[d(TGGGGT)]₄ complexes and useful guidelines for design of efficient anticancer agents but also demonstrates the utility of ESI‐MS as a powerful tool for evaluating interaction between ligand and quadruplex DNA. Copyright © 2012 John Wiley & Sons, Ltd.     

Silver (Ι)‐assisted enantiomeric analysis of ginsenosides using electrospray ionization tandem mass spectrometry

For identification of ginsenoside enantiomers, electrospray ionization mass spectrometry (ESI‐MS) was used to generate silver complexes of the type [ginsenoside + Ag]⁺. Collision induced dissociation of the silver‐ginsenoside complexes produced fragment ions by dehydration, allowing differentiation of ginsenoside enantiomers by the intensity of [M + Ag ? H₂O]⁺ ion. In the meanwhile, an approach based on the distinct profiles of enantiomer‐selective fragment ion intensity varied with collision energy was introduced to refine the identification and quantitation of ginsenoside enantiomers. Five pairs of enantiomeric ginsenosides were distinguished and quantified on the basis of the distribution of fragment ion [M + Ag ? H₂O]⁺. This method was also extended to the identification of other type of ginsenoside isomers such as ginsenoside Rb2 and Rb3. For demonstrating the practicability of this novel approach, it was utilized to analyze the molar ratio of 20‐(S) and 20‐(R) type enantiomeric ginsenosides in enantiomer mixture in red ginseng extract. The generation of characteristic fragment ion [M + Ag ? H₂O]⁺ likely results from the reduction of potential energy barrier of dehydration because of the catalysis of silver ion. The mechanism of enantiomer identification of ginsenosides was discussed from the aspects of computational modeling and internal energy. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

Analysis of O-glucuronide conjugates in urine by electrospray ion trap mass spectrometry

The application of electrospray ionization (ESI) ion trap mass spectrometry in the characterization of O-glucuronide conjugates of some drugs in urine is described. The conjugated metabolites formed in rabbit and human were separated by reversed-phase high-performance liquid chromatography (HPLC) and characterized by multi-stage mass spectrometry (MSⁿ) experiments in negative ion mode. The ESI mass spectra showed a deprotonated molecule [M–H]^–, which was chosen as precursor ion. Collision-induced dissociation (CID) of [M–H]^– in MSⁿ experiments resulted in the appearance of glucuronate ‘fingerprint’ ions at m/z 175 and 113 as well as prominent aglycone ions which were the same as those produced from authentic specimens. This information can be used to identify this type of compound directly without the need for derivatization or hydrolysis of enzymes, providing a rapid and specific method for guiding the isolation and characterization of similar compounds in complex matrices with LC/MS.     

Gas‐phase fragmentation of γ‐lactone derivatives by electrospray ionization tandem mass spectrometry

Fragmentation reactions of β‐hydroxymethyl‐, β‐acetoxymethyl‐ and β‐benzyloxymethyl‐butenolides and the corresponding γ‐butyrolactones were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) using collision‐induced dissociation (CID). This study revealed that loss of H₂O [M + H ?18]⁺ is the main fragmentation process for β‐hydroxymethylbutenolide (1) and β‐hydroxymethyl‐γ‐butyrolactone (2). Loss of ketene ([M + H ?42]⁺) is the major fragmentation process for protonated β‐acetoxymethyl‐γ‐butyrolactone (4), but not for β‐acetoxymethylbutenolide (3). The benzyl cation (m/z 91) is the major ion in the ESI‐MS/MS spectra of β‐benzyloxymethylbutenolide (5) and β‐benzyloxymethyl‐γ‐butyrolactone (6). The different side chain at the β‐position and the double bond presence afforded some product ions that can be important for the structural identification of each compound. The energetic aspects involved in the protonation and gas‐phase fragmentation processes were interpreted on the basis of thermochemical data obtained by computational quantum chemistry. Copyright © 2009 John Wiley & Sons, Ltd.     

Rapid characterization of triterpene saponins from Conyza blinii by liquid chromatography coupled with mass spectrometry

Conyza blinii Le'vl is a medicinal herb used for the treatment of inflammation in Chinese folk medicine. Its major bioactive constituents are triterpene saponins, most of which contain 6–8 sugar residues. In this report, electrospray ionization tandem mass spectrometry fragmentation behaviors of bisdesmosidic triterpene saponins (conyzasaponin A, B, and C) were studied in both positive and negative ion modes with an ion‐trap mass spectrometer. In full scan mass spectrometry, these saponins gave predominant [M–H]^? and [M+Na]⁺ ions, which determined the molecular weights. In tandem mass spectrometry (MSⁿ, n = 2–4), the [M–H]^? and [M+Na]⁺ ions yielded fragments [Y_0α–H]^? and [B_α+Na]⁺, which were diagnostic for the structures of the triterpene skeleton and sugar chains. The structural elucidation was approved by accurate mass data using IT‐TOF‐MS. An interpretation guideline based on MSⁿ (n = 2–4) diagnostic ions was proposed in order to elucidate the chemical structures of unknown triterpene saponins in C. blinii extract. The saponins in C. blinii were separated by liquid chromatography with a methanol/acetonitrile/water solvent system, and then analyzed by ion‐trap and IT‐TOF mass spectrometers. Based on the interpretation guideline, a total of 35 triterpenoid saponins were tentatively identified. Among them, 15 saponins had been previously reported, and the other 20 saponins were reported from Conyza species for the first time. This study indicates that LC/MS is a powerful technology for the rapid characterization of complicated saponins in herbal extracts. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydralazine derivative of aldehyde: A new type of [M − H]+ ion formed in electrospray ionization mass spectrometry

Hydralazine has been widely employed in the development of drugs, derivatization reagents, and ligands. In the present work, we reported a new type of dehydrogenated ion [M ? H]⁺ that was produced from the hydralazine derivative of hexanal in electrospray ionization mass spectrometry (ESI‐MS). The formation of [M ? H]⁺ ions in the ESI‐MS was found to be independent on the mobile phase composition of the liquid chromatography and ESI source parameters. A series of hydralazine derivatives of aldehyde were investigated to confirm this phenomenon. The results showed that hydralazine derivatives of aldehydes that contained an sp³ hybridization carbon with a hydrogen at the α‐position of aldehydes could form the unexpected [M ? H]⁺ ions, whereas hydralazine derivative of acetone could only generate [M + H]⁺ ion in the ESI‐MS. We proposed the possible formation mechanism of [M ? H]⁺ ion for the hydralazine derivatives of aldehydes: the [M ? H]⁺ ion was possibly formed by the loss a hydrogen molecule (H₂) from the protonated ion [M + H]⁺. The results obtained from density functional theory (DFT) calculations supported this proposed formation mechanism of [M ? H]⁺ ion.