The application of liquid chromatography-electrospray ionization mass spectrometry and collision-induced dissociation in the structural characterization of acylated flavonol O-glycosides from the seeds of Carrichtera annua

The flavonoid fraction from the seeds of Carrichtera annua was studied using high-performance liquid chromatography simultaneously coupled to a photodiode array detector (LC/UV-DAD) and a mass spectrometer equipped with an electrospray source (LC/ESI-MS). Collision-induced dissociation (CID) mass spectral data obtained off-line by nanospray (nano-ESI) analysis provided a wealth of complementary structural information, which was consistent with structures established by NMR or led to the proposal of base structures of the flavonol O-glycosides present in the Carrichtera annua seed extract. The flavonoid fraction was found to contain 12 structurally related flavonol O-glycosides. Eleven flavonoids, of which several were new compounds, were acylated with one or more benzoyl, feruloyl or sinapoyl groups. These acyl groups gave rise to characteristic product ions in the [M + H](+) and [M + Na](+) CID spectra as well as to radicalar acid-related product ions at high-energy collisional activation. In addition to the characterization of the acyl substituents, the mass spectral data allowed the identification of the aglycone, the determination of the base structure and the differentiation of several positional isomers.     

Differentiation of a pair of diastereomeric tertiarybutoxycarbonylprolylproline ethyl esters by collision-induced dissociation of sodium adduct ions in electrospray ionization mass spectrometry and evidence for chiral recognition by ab initio molecular orbital calculations

The fragmentation of the sodium adduct ions for tert-butoxycarbonyl-L-prolyl-L-proline ethyl ester (Boc-L-Pro-L-Pro-OEt) was compared with that for Boc-D-Pro-L-Pro-OEt in positive-ion electrospray ionization (ESI) mass spectrometry. In the collision-induced dissociation (CID) mass spectra of the [M + Na](+) ions, the abundance of the [M + Na - C(CH(3))(3) + H](+) ion, which is due to the loss of a tert-butyl group from the [M + Na](+) ion for Boc-D-Pro-L-Pro-OEt, was about eight times higher than that for Boc-L-Pro-L-Pro-OEt. In addition, in the CID spectra of the sodium adduct fragment ion ([M + Na - Boc + H](+)), the abundance of the [M + Na - Boc - prolylresidue + H](+) ion, which is due to the loss of prolyl residue from the [M + Na - Boc + H](+) ion for Boc-L-Pro-L-Pro-OEt, was about five times higher than that for Boc-D-Pro-L-Pro-OEt. These results indicate that Boc-L-Pro-L-Pro-OEt was distinguished from Boc-D-Pro-L-Pro-OEt by the CID mass spectra of the sodium adduct ions in ESI mass spectrometry. The optimized geometries of the [M + Na](+) and the [M + Na - Boc + H](+) ions calculated by ab initio molecular orbital calculations suggest that the chiral recognition of these diastereomers was due to the difference of the orientation of a sodium ion to the oxygen and nitrogen atoms in dipeptide derivatives, and to the difference of the total energies between them.     

Mass spectral analysis of N-oxides of Chemical Weapons Convention related aminoethanols under electrospray ionization conditions

N,N'-Dialkylaminoethanols are the hydrolyzed products or precursors of chemical warfare agents such as V-agents and nitrogen mustards, and they are prone to undergo oxidation in environmental matrices or during decontamination processes. Consequently, screening of the oxidized products of aminoethanols in aqueous samples is an important task in the verification of chemical weapons convention-related chemicals. Here we report the successful characterization of the N-oxides of N,N'-dialkylaminoethanols, alkyl diethanolamines, and triethanolamine using positive ion electrospray ionization mass spectrometry. The collision-induced dissociation (CID) spectra of the [M+H](+) and [M+Na](+) ions show diagnostic product ions that enable the unambiguous identification of the studied N-oxides, including those of isomeric compounds. The proposed fragmentation pathways are supported by high-resolution mass spectrometry data and product/precursor ion spectra. The CID spectra of [M+H](+) ions included [MH-CH(4)O(2)](+) as the key product ion, in addition to a distinctive alkene loss that allowed us to recognize the alkyl group attached to the nitrogen. The [M+Na](+) ions show characteristic product ions due to the loss of groups (R) attached to nitrogen either as a radical (R) or as a molecule [R+H or (R-H)] after hydrogen migration.     

Characterization of sodiated glycerol phosphatidylcholine phospholipids by mass spectrometry

Fast atom bombardment mass spectrometry in the positive mode was used for the characterization of sodiated glycerol phosphatidylcholines. The relative abundance (RA) of the protonated species is similar to the RA of the sodiated molecular species. The sodiated fragment ion, [M + Na - 59](+), corresponding to the loss of trimethylamine, and other sodiated fragment ions, were also observed. The decomposition of the sodiated molecule is very similar for all the studied glycerol phosphatidylcholines, in which the most abundant ion corresponds to a neutral loss of 59 Da. Upon collision-induced dissociation (CID) of the [M + Na](+) ion informative ions are formed by the losses of the fatty acids in the sn-1 and sn-2 positions. Other major fragment ions of the sodiated molecule result from loss of non-sodiated and sodiated choline phosphate, [M + Na - 183](+), [M + Na - 184](+.) and [M + Na - 205](+), respectively. The main CID fragmentation pathway of the [M + Na - 59](+) ion yields the [M + Na - 183](+) ion, also observed in the CID spectra of the [M + Na](+) molecular ion. Other major fragment ions are [M + Na - 205](+) and the fragment ion at m/z 147. Collisional activation of [M + Na - 205](+) results in charge site remote fragmentation of both fatty acid alkyl chains. The terminal ions of these series of charge remote fragmentations result from loss of part of the R(1) or R(2) alkyl chain. Other major informative ions correspond to acylium ions.     

Evaluation of glycosylation and malonylation patterns in flavonoid glycosides during LC/MS/MS metabolite profiling

Flavonoid conjugates constitute several classes of plant phenolic secondary metabolites including many isomeric compounds differing in the hydroxylation pattern and substitution of their rings with different groups such as alkyls, acyls or sugars. These compounds occur in plant tissues mainly as glycosides and in many cases it is necessary to have reliable and detailed information concerning the structure of these natural products. Our results were obtained using leaf extracts of Arabidopsis thaliana and Lupinus angustifolius in which different glycosides of flavones, flavonols and isoflavones are present. Analysis of collision-induced dissociation (CID)/MS/MS spectra of protonated [M + H](+), sodiated [M + Na](+) or deprotonated [M - H](-) molecules recorded during HPLC runs may bring needed information in this respect. However, registration of mass spectra of [M + Na](+) ions with a good efficiency is possible only after post-column addition of a sodium acetate solution to the LC column eluate. The retention of sodium cation on the saccharidic parts of the molecule is observed after the CID fragmentation. In many cases, the location of this cation on the glycan attached to C-3 hydroxyl group of flavonol led to assignment of its structure. Additionally, the determination of the structure of the aglycone and of the sequence of the glycan part was made possible through the CID data obtained from the [M + H](+) and [M - H](-) ions. CID spectra show a different order of sugar elimination from hydroxyl groups at C-3 and C-7 in flavonol glycosides isolated from A. thaliana leaves and give sufficient information to discriminate flavonoid O-diglycosides from flavonoid di-O-glycosides.     

Mass spectral studies of N,N-dialkylaminoethanols

Some dialkylaminoethanols, precursors of chemical warfare agents such as V-agents and nitrogen mustards, were analyzed by electron impact (EI) and electrospray ionization (ESI) mass spectrometry. The fragmentation pathways in EI and ESI-MS/MS methods are rationalized. The collision-induced dissociation (CID) spectra of [M+H](+) ions of aminoethanols in ESI mode are clearly distinguishable from one another, including those of isomeric normal and branched chain dialkylaminoethanols. Structures can be proposed based on the general fragmentation pathways of these molecules.     

Regiospecific analysis of neutral ether lipids by liquid chromatography/electrospray ionization/single quadrupole mass spectrometry: validation with synthetic compounds.

A reversed-phase high-performance liquid chromatography (HPLC) method with on-line electrospray ionization/collision-induced dissociation/mass spectrometry (ESI/CID/MS) is presented for the regiospecific analysis of synthetic reference compounds of neutral ether lipids. The reference compounds were characterized by chromatographic retention times, full mass spectra, and fragmentation patterns as an aid to clarify the regiospecificity of ether lipids from natural sources. The results clearly show that single quadrupole mass spectroscopic analysis may elucidate the regiospecific structure of neutral ether lipids. Ether lipid reference compounds were characterized by five to six major ions in the positive ion mode. The 1-O-alkyl-sn-glycerols were analyzed as the diacetoyl derivative, and showed the [M - acetoyl](+) ion as an important diagnostic ion. The diagnostic ions of directly analyzed 1-O-alkyl-2-acyl-sn-glycerols and 1-O-alkyl-3-acyl-sn-glycerols were the [M - alkyl](+), [M + H - H(2)O](+) and [M + H](+) ions. Regiospecific characterization of the fatty acid position was evident from the relative ion intensities, as the sn-2 species had relatively high [M + H](+) ion intensities compared with [M + H - H(2)O](+), whereas the reverse situation characterized the sn-3 species. Furthermore, corresponding sn-2 and sn-3 species were separated by the chromatographic system. However, loss of water was promoted as fatty acid unsaturation was raised, which may complicate interpretation of the mass spectra. The diagnostic ions of directly analyzed 1-O-alkyl-2,3-diacyl-sn-glycerols were the [M - alkyl](+), [M - sn-2-acyl](+) and [M - sn-3-acyl](+) ions. Regiospecific characterization of the fatty acid identity and position was evident from the relative ion intensities, as fragmentation of the sn-2 fatty acids was preferred to the sn-3 fatty acids; however, loss of fatty acids was also promoted by higher degrees of unsaturation. Therefore, both structural and positional effects of the fatty acids affect the spectra of the neutral ether lipids. Fragmentation patterns and optimal capillary exit voltages are suggested for each neutral ether lipid class. The present study demonstrates that reversed-phase HPLC and positive ion ESI/CID/MS provide direct and unambiguous information about the configuration and identity of molecular species in neutral 1-O-alkyl-sn-glycerol classes.     

Differentiation of diasteromeric α-sulfanyl-β-amino acid derivatives by electrospray ionization tandem mass spectrometry

A set of diastereomeric α-sulfanyl-β-amino acid derivatives, which are important building blocks for pharmaceuticals with potent biological activity, are studied by electrospray ionization tandem mass spectrometry. The collision induced dissociation (CID) spectra of [M+H](+), [M+NH(4)](+), [M+Na](+) and [M+Li](+) of the diastereomers were studied, among them the CID of [M+Na](+) and [M+Li](+) showed consistent differences in the relative abundance of characteristic ions that enabled distinction of the anti isomers from syn isomers. The decomposition pathways for the diagnostic ions were arrived at based on high-resolution mass spectrometry data, multiple mass spectrometry data, deuterium labeling experiments and the mass shift in accordance with the substituents located at different places. Loss of (R(1)-C(6)H(4)-CH=NH) and (Cat-NH-SO(2)R(2)) from [M+Cat](+), where Cat=Na and Li, and the product ions as a results of McLafferty rearrangement involving either >S=O or >C=O group were found to be diagnostic. The McLafferty rearrangement product ions involving >S=O group were more abundant in syn isomers while those involving >C=O group were more abundant in anti isomer. The selectivity observed in the decomposition of [M+Li](+) ions was found to be similar to that of [M+Na](+) ions, but in few cases the differences are marginal in the decomposition [M+Li](+) ions.     

Structural determination of saponins extracted from starfish by fast atom bombardment collision-induced dissociation mass spectrometry.

Three saponins were extracted and isolated from starfish by reversed-phase high performance liquid chromatography (HPLC), and analyzed by fast atom bombardment mass spectrometry (FAB-MS). Their molecular weight information could be obtained by the presence of abundant [M+Na]+ ions and weak [M+H]+ ions in FAB-MS spectra. Moreover, high resolution mass measurements of their [M+Na]+ ions were performed at the resolution of 10000 to elucidate the element composition of extracted saponins. The collision-induced dissociation (CID) of sodium-adducted molecules [M+Na]+ yielded diverse product ions via dissociated processes. In the collision-induced dissociation (CID)-MS/MS analysis of [M+Na]+ ion, the sulfate-containing saponins produced characteristic ions such as SO4Na+, [NaHSO4+Na]+, [M+Na-sugar]+ and [M+Na-2sugar]+ ions, whereas the sulfate-free compound showed characteristic ions produced by cleavage of sugar moiety and side chain of aglycone. The fragmentation patterns could provide information on the linkage position of sugar groups in aglycone and sulfate groups.     

Structural determination of lysophosphatidylcholines extracted from marine sponges by fast atom bombardment tandem mass spectrometry

A series of lysophosphatidylcholines were isolated from the marine sponge Spirastrella abata by reversed-phase high performance liquid chromatography (HPLC) and analyzed by fast atom bombardment mass spectrometry (FAB-MS). Their structural elucidation was carried out with fast atom bombardment tandem mass spectrometry (FAB-MS/MS). The collision-induced dissociation (CID) of protonated and sodiated molecular ions produced diverse product ions via a series of dissociative processes. Because of the positive charge of the amine group at the end of the molecules, charge-remote fragmentation patterns of specific ions, [M + H](+) or [M + Na](+), were very helpful for the identification of product ions which are characteristic for choline and long hydrocarbon chains substituted at the glycerol back bone. Moreover, the CID-MS/MS spectra of sodium adducted molecular ions for lysophosphatidylcholines yielded common characteristic fragment ions for the choline moiety and characteristic ions [M + Na-103](+), [M + Na-85](+) and [M + Na-59](+) in the higher mass region.     

Fragmentation study of iridoid glucosides through positive and negative electrospray ionization, collision-induced dissociation and tandem mass spectrometry

Mass spectrometric methodology based on the combined use of positive and negative electrospray ionization, collision-induced dissociation (CID) and tandem mass spectrometry (MS/MS) has been applied to the mass spectral study of a series of six naturally occurring iridoids through in-source fragmentation of the protonated [M+H]+, deprotonated [M--H]- and sodiated [M+Na]+ ions. This led to the unambiguous determination of the molecular masses of the studied compounds and allowed CID spectra of the molecular ions to be obtained. Valuable structural information regarding the nature of both the glycoside and the aglycone moiety was thus obtained. Glycosidic cleavage and ring cleavages of both aglycone and sugar moieties were the major fragmentation pathways observed during CID, where the losses of small molecules, the cinnamoyl and the cinnamate parts were also observed. The formation of the ionized aglycones, sugars and their product ions was thus obtained giving information on their basic skeleton. The protonated, i.e. [M+H]+ and deprotonated [M--H]-, ions were found to fragment mainly by glycosidic cleavages. MS/MS spectra of the [M+Na]+ ions gave complementary information for the structural characterization of the studied compounds. Unlike the dissociation of protonated molecular ions, that of sodiated molecules also provided sodiated sugar fragments where the C0+ fragment corresponding to the glucose ion was obtained as base peak for all the studied compounds.     

Determination of the glycosylation site in flavonoid mono-O-glycosides by collision-induced dissociation of electrospray-generated deprotonated and sodiated molecules

The influence of the glycosylation site on the fragmentation behavior of 18 flavonoid glycoside standards was studied using positive and negative electrospray ionization mass spectrometry in combination with collision-induced dissociation and tandem mass spectrometry. The glycosylation position is shown to affect the relative abundance of the radical aglycone ions that can be observed in the [M-H]- collision-induced dissociation spectra. In particular, the radical aglycone ions are very abundant for deprotonated flavonol 3-O-glycosides. Collisional activation of the radical aglycone ions produced from positional isomers revealed minor differences: m,nB0- product ions are pronounced for 7-O-glycosides, whereas m,nA0- product ions are relatively more abundant for 4'-O-glycosides. In addition, the ratio between the radical aglycone and the regular aglycone ions in the [M+Na]+ high-energy collision-induced dissociation spectra gives an indication about the glycosylation site. This ion ratio allows the differentiation between flavonoid 3-O- and 7-O-glycosides or can be useful in the comparison of unknown compounds with standards. Unambiguous differentiation between O-glycosylation at the common positions of flavonoid O-glycosides, i.e. the 3-, 4'- and 7-positions, is achieved by collisional activation of sodiated molecules at high collision energy. The presence of a B-ring product ion containing the sugar residue indicates 4'-O-glycosylation, whereas the loss of the B-ring part from the aglycone product ion is characteristic of 3-O-glycosylation and the loss of the B-ring part from both the [M+Na]+ precursor ion and the aglycone product ion points to 7-O-glycosylation.     

Data-directed scan sequence for the general assignment of C-glycosylflavone O-glycosides in plant extracts by liquid chromatography-ion trap mass spectrometry

An ion trap LC-MS/MS method is described for the analysis of C-glycosylflavone O-glycosides in crude methanolic extracts of plants. The method employs survey scans with and without the application of up-front collision induced dissociation (CID) to generate diagnostic ions for data-directed MS/MS. The spectra acquired allow assignment of the C-linked sugar to either the C-6 or C-8 position of the aglycone and provide data on the molecular mass of the compound, the number and type of O-linked sugars and the molecular mass of the flavone aglycone. These data for the majority of C-glycosylflavone O-glycosides in an extract are obtained automatically in one LC-MS/MS analysis without manual pre-programming. Key to the assignment of the C-6 or C-8 site of C-glycosylation is the generation, by up-front CID, of the (0,1)X+ product ion formed by internal cleavage of the C-linked sugar. MS/MS of this ion is found to have diagnostic value in addition to the (0,2)X+ product ion described by other authors. Ion trap MS/MS spectra of [M+H]+ of the 6,8-di-C-glycosylflavones schaftoside and isoschaftoside show an additional and previously unreported diagnostic product ion that is useful in determining the type of sugar at the C-6 position. The product ion spectra of protonated kaempferol 3-O-glucosylrhamnosides show similarities to the spectra of C-glycosylflavone O-glycosides; this is a potential source of confusion if the analysis of such glycosides is limited solely to MS/MS of [M+H]+.     

Study of structural characteristic features of phenanthriondolizidine alkaloids by fast atom bombardment with tandem mass spectrometry

The mass spectrometric behavior of phenanthroindolizidine alkaloids has been investigated in detail by positive ion fast atom bombardment tandem mass spectrometry (FAB-MS/MS) combined with collision-induced dissociation (CID). The fragmentation has been correlated with the skeleton structure and positions of substituents. The product ions arising from retro-Diels-Alder cleavages differ clearly for compounds with different skeletons. The substituents at C-14 were observed to markedly influence the fragmentation pathway of [M + H](+) ions. A diversity of dissociation behavior initiated by the variation of substituents on the aromatic ring was also observed in the CID spectra. Product ions resulting from loss of CH(4) were obtained for compounds in which both C-6 and C-7 are occupied by methoxy groups. FAB-MS/MS spectra can reflect the connection between the fragmentation behavior and structural features of these phenanthroindolizidine alkaloids rapidly and effectively, and should prove to be a powerful method to determine the structures of related compounds.     

Fragmentation study of salinomycin and monensin A antibiotics using electrospray quadrupole time-of-flight mass spectrometry

The fragmentation pathways of two selected ionophore antibiotics, salinomycin and monensin A, were studied using electrospray (ES) orthogonal acceleration quadrupole time-of-flight mass spectrometry in positive-ion mode. The identity of fragment ions was determined by accurate-mass measurements. In ES mass spectra, ion signals of relatively high intensity were observed for [M+Na](+) and [M-H+2Na](+) for each antibiotic. Each of the ion species [M+Na](+) and [M-H+2Na](+) for salinomycin and [M-H+2Na](+) for monensin A were isolated in turn and subjected to fragmentation. In the fragmentation of [M+Na](+) and [M-H+2Na](+) from salinomycin, only Cbond;C single bond cleavage and dehydration were observed. Product ion mass spectra obtained from [M-H+2Na](+) of monensin A showed that ether ring opening, Cbond;C single bond cleavage and dehydration fragmentations had occurred. Fragment ions containing two sodium atoms were observed in the product ion mass spectrum of [M-H+2Na](+) from salinomycin, but not from monensin A. Both type A (containing the terminal carboxyl group) and type F (containing the terminal hydroxyl group) fragment ions were observed in the product ion mass spectra of sodium adduct ions of salinomycin and monensin A.     

Analysis of triacylglycerols with non-aqueous reversed-phase liquid chromatography and positive ion electrospray tandem mass spectrometry

A non-aqueous reversed-phase liquid chromatographic method coupled to electrospray ionisation (ESI) tandem mass spectrometry was developed for the analysis of triacylglycerols (TGs). The synthetic TGs studied were separated according to their equivalent carbon number with a gradient of methanol (containing 0.01% (v/v) formate adjusted to pH 5.3 with ammonia) and chloroform. ESI mass spectra of TGs yielded positive ion current signals for [M + NH(4)](+) and [M + NH(4)-RCOONH(4)](+). The mass spectra also showed signals believed to arise from [M + K](+). Collision-induced dissociation (CID) of the [M + NH(4)](+) precursor ion yielded [M + NH(4) - RCOONH(4)](+), [RCO + 74](+) and [RCO](+) product ions as aids for the structural elucidation of the TGs. In addition, [RCO - 18](+) and small amounts of [RCO - 2](+) product ions were also found. The latter ions were observed only for TGs containing unsaturated fatty acids. CID of ammoniated 1-stearoyl-2-oleoyl-3-linoleoyl-glycerol (18:0/18:1/18:2) indicated that neutral loss of the sn-2 fatty acid was energetically less favourable than loss of the fatty acid from the sn-1 or sn-3 position.     

Structural determination of hexadecanoic lysophosphatidylcholine regioisomers by fast atom bombardment tandem mass spectrometry

The structural determination of sn-1 and sn-2 hexadecanoic lysophosphatidylcholine (LPC) regioisomers was carried out using fast atom bombardment tandem mass spectrometry (FAB-MS/MS). The collision-induced dissociation (CID) of protonated and sodiated molecules produced diverse product ions due mainly to charge remote fragmentations. Based on the information obtained from the CID spectra of protonated and sodiated molecules, sn-1 and sn-2 hexadecanoic LPC isomers could be discriminated. Especially, the abundance ratio of the diagnostic ion pair [m/z 224/226] in the CID spectra of [M + H](+) ions was shown to be greatly different. Moreover, the CID-MS/MS spectra of sodium-adducted molecules for hexadecanoic LPC isomers showed characteristic product ions such as [M + Na - 103](+), [M + Na - 85](+), and [M + Na - 59](+), by which their regio-specificity can be differentiated.     

Fragmentation patterns of newly isolated cassane butenolide diterpenes and differentiation of stereoisomer by tandem mass spectrometry

Different stereoisomers of active molecules often cause different physiological responses and hence pose a challenge for their identification. This study involves perceptive fragmentation behavior of newly isolated cassane butenolides, caesalpinolide A [1] and caesalpinolide B [2] (epimeric at the hemiketal position) by tandem MS. The electrospray ionization-mass spectrometry (ESI-MS)/collision-induced dissociation (CID; ESI-MS(2) and ESI-IT-MS(n)) were investigated. The effect of orientations of hemiketal hydroxyl at C-12 was clearly observed in the mass spectrum. Tandem mass spectra of 1, 1(A) or 2, 2(A) show stereospecific fragmentation resulting in significant abundance dissimilarity of [MH - H(2)O](+) as well as differences in fragmentation pathway. Both of these pathways seem to be influenced by the stereochemistry of the molecule. The differentiation can be clearly visualized from the [M + H - H(2)O](+)/[M + H](+) ratio of the two isomers where beta-isomer 2 was found to be five times higher than that of alpha-isomer 1 in full scan liquid chromatography-electrospray ionization mass spectrometry(LC-ESI-MS). In high-energy CID, the mass fingerprint of 1, 2, 1(A), and 2(A) was found to be different from one another.     

Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra

Cluster ions such as [Cat+X+nM](+) (n = 0-4); [Cat-H+nM](+) (n = 1-3); and [2(Cat-H)+X+nM](+) (n = 0-2), where Cat, X, and M are the dication, anion, and neutral salt (CatX(2)), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H](+), one-electron reduction of the dication to form Cat(+.), demethylation of the paraquat cation to form [Cat-CH(3)](+), and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H](+) and its clusters) and odd-electron (mostly Cat(+)) ions in ESI mass spectra of these pesticides. The [Cat+n. Solv](2+) doubly charged cluster ions, where n 相似文献   

Hydrogen-deuterium exchange reactions of cis- and trans-cyclopropane derivatives with D(2)O and CD(3)OD in the gas phase

Gas-phase hydrogen-deuterium (H/D) exchange reactions involving four isomeric cyclopropane derivatives were investigated under chemical ionization (CI) conditions, using D(2)O and CD(3)OD as reagent gases. There are abundant ions at [M + 1](+), [M + 2](+) and [M + 3](+) in the D(2)O and CD(3)OD positive-ion CI mass spectra of the two isomer pairs 1, 2 and 3, 4. Their CI mass spectra are identical with each pair, and so are the collision-induced dissociation (CID) spectra of ions [M + 1](+), [M + 2](+) and [M + 3](+) of each of the two isomer pairs. The CID spectra of [M + 1](+) ions indicate that they have common D/H exchange reactions within each pair, which take place between molecular ions and deuterium-labeling reagents to form the [M - H + D](+) ions. Those of their [M + 2](+) ions show that they have common D/H exchange reactions within each pair, which form the [M(d1) + H](+) ions. Those of their [M + 3](+) ions show that they have common D/H exchange reactions within each pair, which take place between the [M(d1)] and deuterium-labeling reagents to produce [M(d2) + H](+) for the isomer pair 1, 2 and [M(d1) + D](+) for the isomer pair 3, 4. The number and position, and active order of the active hydrogen atoms of the isomer pairs 1, 2 and 3, 4 were determined. Copyright 2000 John Wiley & Sons, Ltd.