A fragmentation study of podophyllotoxin and its 4'-demethyl-4beta-substituted derivatives by electrospray ionization ion-trap time-of-flight tandem mass spectrometry

High-resolution electrospray ionization multistage tandem mass spectrometry (MS(1-9)) was used to determine the accurate masses and the fragmentation pathways of protonated podophyllotoxin (1) and its corresponding 4'-demethyl-4beta-substituted derivatives (2-4). The protonated molecules, [M + H](+), of all the four compounds were observed in the conventional single-stage mass spectra. Two fragmentation pathways, that appear to be characteristic of the four compounds, are proposed on the basis of their multistage tandem mass spectrometric data. The characteristic elimination, from the precursor protonated ions, of the neutral groups 4-R(1)H, 1-ArH, CO, CH(2)O and C(4)H(4)O(2), in which R is located on C-4, is the common elimination, and the product ions at m/z 267, 239, 229, 181, 173, 153, 143 and 115 are the common diagnostic masses. The elimination of the R(1) group substituent located on the C-4 position of compounds 1-4 has a significant influence on the fragmentation pathway obtained in the conventional single-stage mass spectra. A large R(1) group would be unfavorable for this elimination, unless the collision energy is raised. Apart from the common fragmentations obtained for the protonated molecules 1-4, significant additional product ions were detected in the various multistage tandem mass spectrometric analyses, particularly in the case of the product ions derived initially from the phenolic hydroxyl group of 2-4, which are different from those of 1. Based on these additional formed product ions, several additional fragmentation pathways for 1 or 2-4 are also presented.     

Characterization of acylated flavonoid-O-glycosides and methoxylated flavonoids from Tagetes maxima by liquid chromatography coupled to electrospray ionization tandem mass spectrometry

Liquid chromatography coupled to negative electrospray ionization (ESI) tandem mass spectrometry (MS/MS) employing a triple quadrupole mass spectrometer was used in the structural determination of acylated flavonoid-O-glycosides and methoxylated flavonoids occurring in Tagetes maxima. The compounds were identified by experiments in full scan mode (MS), and tandem mass experiments (MS/MS) of precursor ion scan, product ion scan, and neutral loss scan modes. In order to characterize the aglycones of the flavonoid glycosides, in-source fragmentation of the deprotonated molecule [M-H]- followed by product ion scan of the resulting aglycone [A-H]- were performed. This combined approach allowed the identification of 51 phenolic compounds, including flavonoid-O-glycosides acylated with galloyl, protocatechuoyl, coumaroyl or caffeoyl groups, methoxylated flavonoids, and hydroxycinnamic acid and phenolic acid derivatives, none of them previously reported in Tagetes maxima.     

A non-covalent dimer formed in electrospray ionisation mass spectrometry behaving as a precursor for fragmentations

A non-covalent-bonded dimer was detected in the positive ion electrospray ionisation (ESI) mass spectra of a synthetic impurity. In tandem mass spectrometry (MS/MS) experiments using collision-induced dissociation (CID), the ion was found to behave as a [M+H]+-type precursor ion for fragmentation until MS5. The dimer was probably formed through multi-hydrogen bonds over a proton bridge. When the fragmentation occurred at the center of the bridge, the dimer was broken apart to give monomer fragments at MS6. However, no corresponding deprotonated dimer [2M-H]- was found in the negative ion ESI spectra. The dimer was extremely stable, and it could still be observed when a fragmentation voltage of up to 50 V was applied in the ionisation source. The formation of the non-covalent dimer was also found to be instrument-dependent, but independent of sample concentration. Accurate mass measurements of the [2M+H]+ and [M+H]+ ions, and their MSn product ions, provided the basis for assessing the fragmentation mechanism proposed for [2M+H]+. The fragmentation pathway was also illustrated for the deprotonated molecule [M-H]-.     

Use of solid-phase extraction, reverse osmosis and vacuum distillation for recovery of aromatic sulfonic acids from aquatic environment followed by their determination using liquid chromatography-electrospray ionization tandem mass spectrometry

Three different sample preparation techniques (i) solid-phase extraction, (ii) reverse osmosis and (iii) vacuum distillation have been investigated and the recoveries were compared for determination of highly water-soluble benzene and stilbene sulfonic acids in aqueous environment by liquid chromatography with photodiode array (PDA) and electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The recoveries were quite high using vacuum distillation (>90%) compared to solid phase extraction and reverse osmosis. The negative ion ESI mass spectra containing the peaks of quasimolecular ion [M-H]- allow the molecular mass determination of unknown compounds whereas the structures were proposed using fragments obtained from MS/MS analysis of [M-H]- ions. At lower fragmentation voltages only the quasimolecular ion [M-H]- was observed and as fragmentation voltages increased, it led to the formation of fragment ions corresponding to [M-H-SO3]-, [M-H-SO2]-, and SO3-. The detection limits were 1-28 microg/L with LC-ESI-MS. The sample collected from wastewater treatment plant was found to contain 21.1, 13.3, 12.1, 41.8 and 9.9 microg/L of cis-4,4(l)-diaminostilbene-2,2(l)-disulfonic acid (cis-DASDA), trans-4,4(l)-diaminostilbene-2,2(l)-disulfonic acid (trans-DASDA), 3-amino acetanilide-4-sulfonic acid (3-AASA), 4-chloroaniline-2-sulfonic acid (4-CASA), 2-chloroaniline-5-sulfonic acid (2-CASA), respectively.     

Liquid chromatography/electrospray ionization mass spectrometry for the characterization of twenty-three flavonoids in the extract of Dalbergia odorifera

A method incorporating high-performance liquid chromatography (HPLC) with electrospray ionization and tandem mass spectrometry, with parallel analysis by HPLC with UV detection using a diode-array detector, was developed for the qualitative characterization of flavonoids in D. odorifera. Twenty-three flavonoids, including six isoflavones, six neoflavones, four isoflavanones, three flavanones, two chalcones, one isoflavanonol and one pterocarpan, were unambiguously identified by comparing their retention times, UV and MS spectra with those of authentic compounds. Furthermore, the collision-induced dissociations of the [M-H]- ions were studied to clarify the MS behavior of the different types of flavonoids. In negative ion ESI-MS all the flavonoids yielded prominent [M-H]- ions in the first order mass spectra. Fragments involving losses of CH3*, H2O, CO, C2H2O, and CO2 were observed in the MS/MS spectra. Each of the seven types of flavonoid showed characteristic MS/MS fragmentation patterns. The isoflavanones, flavanones and chalcones were observed to undergo retro-Diels-Alder fragmentations. The spectra of almost all the neoflavonoids unexpectedly exhibited only [M-H-CH3]-* radical anions as base peaks without any further fragmentation. Substitution positions also remarkably influenced the fragmentation behavior, which could assist in distinction among the flavonoid isomers. The fragmentation rules deduced here could aid in the characterization of other flavonoids of these types.     

Chromatographic and mass spectral studies of perfluorooctanesulfonate and three perfluorooctanesulfonamides

The chromatographic and mass spectral characteristics of perfluorooctanesulfonate (PFOS) and three nitrogen-substituted perfluorooctanesulfonamides have been obtained. A methyl/phenyl mixed-phase fused-silica capillary column was used for gas chromatographic (GC) analyses, while a C18 reversed-phase microbore column was used for liquid chromatographic (LC) analyses. Mass (MS) and tandem mass (MS/MS) spectra were generated using electron ionization (EI), argon CE, methane positive and negative ion CI, and ES ionization modes. EI spectra of the amides showed ions characteristic of both the fluorinated hydrocarbon and the sulfonamide portion of the molecules. The fragmentation pathway was studied using hydrogen/deuterium exchange, and was thought to involve a cyclic intermediate ion. Formation of molecular ions by CE and protonated molecule ions by CI to obtain molecular weight information was only partially successful. Negative ion ES-MS spectra provided intense [M-H]- anions for the amides, and an [M-K]- anion for PFOS from which molecular weight information could be obtained, while ES-MS/MS produced product ions that could be used to detect the presence of these compounds in biological or environmental samples.     

Structural characterization of iridoid glucosides by ultra-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry

The mass spectral fragmentation behavior of ten iridoid glucosides (IGs) has been studied using electrospray ionization (ESI), collision-induced dissociation (CID), and quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS). In the negative ESI mass spectra, the deprotonated [M-H](-) ion was observed for all of the ten IGs except gardoside methyl ester, while the formate adduct [M+HCOO](-) ion appeared to be favored by the presence of a methyl ester or a lactone group in the C-4 position when formic acid was added to the mobile phase. The CID MS/MS spectra of the [M-H](-) ions have been used for structural elucidation. Ring cleavages of the aglycone moiety have been observed in the MS/MS spectra, corresponding to (1,4)F(-), (2,6)F(-), (2,7)F(-), and (2,7)F(0) (-) ions, based on accurate mass measurements and the elemental compositions of the product ions. These characteristic ions gave valuable information on the basic structural skeletons. Furthermore, on the basis of the relative abundances of the fragment ions (1,4)F(-) and (2,7)F(-), different sub-classes, such as cyclopentane-type and 7,8-cyclopentene-type IGs, can be differentiated. Ring cleavage of the sugar moieties was also observed, yielding useful information for their characterization. In addition, the neutral losses, such as H(2)O, CO(2), CH(3)OH, CH(3)COOH, and glucosidic units, have proved useful for confirming the presence of functional substituents in the structures of the IGs. Based on the fragmentation patterns of these standard IGs, twelve IGs have been characterized in an extract of Hedyotis diffusa Willd. by means of ultra-performance liquid chromatography/Q-TOF MS/MS, of which six have been unambiguously identified and the other six have been tentatively identified.     

Electrospray ionization ion-trap time-of-flight tandem mass spectrometry of two furofurans: sesamin and gmelinol

High-resolution electrospray ionization multistage tandem mass spectrometry (MS(1-7)) in positive ion mode was used to determine the accurate masses and the fragmentation pathways of two furofurans, sesamin and gmelinol. The protonated molecules [M+H]+ were absent in the conventional mass spectra of both compounds, but two characteristic ions, [M+H-H(2)O]+ and [M+H-H(2)]+, were always observed. Successive losses of CH(2)O and CO are the common characteristic fragmentations. Based on the exact masses acquired from 21 different tandem mass spectra, two or three fragmentation pathways for each compound are proposed. The consecutive losses of two H(2)O molecules and one H(2) molecule readily take place from the furan rings for both sesamin and gmelinol, resulting in the absence of the protonated molecules in the single-stage experiments. HCHO loss is observed at least three times in the tandem mass spectra, mainly from methylenedioxy groups (OCH(2)O) for sesamin but only from tetrahydrofuran rings for gmelinol. Moreover, CO loss is found at least three times in the tandem mass spectra of both sesamin and gmelinol from the 3,4-methylenedioxyphenyl (ArOCH(2)O) moieties for sesamin and from both the dimethoxyphenyl and the tetrahydrofuran ring moieties for gmelinol. In addition, the disubstituted benzyl cation ArCH(2)+ at m/z 135 for sesamin and at m/z 151 for gmelinol was found in the MS(3) spectra of both sesamin and gmelinol, which is very helpful in the identification of the compositions of 3,4-disubstituted groups on the benzene rings of the furofurans.     

Structural analysis of selected characteristic flavones by electrospray tandem mass spectrometry.

Seven structure analogical flavonoid aglycones have been analyzed using electrospray ionization tandem mass spectrometry (ESI-MSn) in the negative-ion mode. The spectra obtained ESI-MSn allowed us to propose plausible schemes for their fragmentation mechanism. By analyzing the product ions spectra of deprotonated molecule ions [M-H](-), some neutral diagnostic losses and specific retro Diels-Alder fragments were obtained. By using all of these characteristic fragment ions we can specially differentiate the flavone isomer.     

Electrospray ionisation mass spectral studies on hydrolysed products of sulfur mustards

Off-site detection of the hydrolysed products of sulfur mustards in aqueous samples is an important task in the verification of Chemical Weapons Convention (CWC)-related chemicals. The hydrolysed products of sulfur mustards are studied under positive and negative electrospray ionisation (ESI) conditions using an additive with a view to detecting them at trace levels. In the presence of cations (Li(+), Na(+), K(+) and NH(4) (+)), the positive ion ESI mass spectra of all the compounds include the corresponding cationised species; however, only the [M+NH(4)](+) ions form [M+H](+) ions upon decomposition. The tandem mass (MS/MS) spectra of [M+H](+) ions from all the hydrolysed products of the sulfur mustard homologues were distinct and allowed these compounds to be characterised unambiguously. Similarly, the negative ion ESI mass spectra of all the compounds show prominent adducts with added anions (F(-), Cl(-), Br(-), and I(-)), but the [M-H](-) ion can only be generated by decomposition of an [M+F](-) ion. The MS/MS spectra of the [M-H](-) ions from all the compounds result in a common product ion at m/z 77. A precursor ion scan of m/z 77 is shown to be useful in the rapid screening of these compounds in aqueous samples at trace levels, even in the presence of complex masking agents, without the use of time-consuming sample preparation and chromatography steps. An MS/MS method developed to measure the detection limits of the hydrolysed products of sulfur mustards found these to be in the range of 10-500 ppb.     

Identification of phenolic constituents in Radix Salvia miltiorrhizae by liquid chromatography/electrospray ionization mass spectrometry

The phenolic components from Radix Salvia miltiorrhizae Bunge, a well-known herbal medicine (Dan-Shen in Chinese), have been investigated by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS). HPLC analyses were performed on a reversed-phase C18 column using gradient elution. In the ESI mass spectra a predominant [M-H]- ion was observed in negative mode and provided molecular mass information. ESI-MS/MS spectra of the [M-H]- ions were used for structural analysis, based on the spectra of standards. It was found that caffeic acid and its monomeric analogs containing a carboxyl group readily lost CO2, while dimers, trimers and tetramers of caffeic acid expelled successively danshensu or caffeic acid or their esters. Twenty-eight phenolic compounds in S. miltiorrhizae were characterized, of which eight compounds were positively identified by comparison with standards. The remaining twenty phenolics for which standards were not available were tentatively identified based on their UV spectra and MS/MS fragmentation characteristics.     

Electrospray ionization and tandem mass spectrometry of cysteinyl eicosanoids: Leukotriene C4 and FOG7

The cysteinyl leukotrienes, LTC4, LTD4 and LTE4, and the recently described cysteinyl eicosanoid, 5-oxo-7-glutathionyl-8,11,14-eicosatrienoic acid (FOG7) have been analyzed by tandem mass spectrometry. Both [M-H]- and [M+H]+ ions were produced by electrospray ionization and collision-induced dissociation of these molecular ion species were studied using both an ion trap and a triple quadrupole instrument. Product ion spectra obtained were characteristic of the structure of the cysteinyl leukotrienes and mechanisms of ion formation were investigated by using deuterium-labeled analogs. The product ion spectrum obtained following collision-induced dissociation of the [M-H]- anion from FOG7 was devoid of significant structural information and further studies of collision activation of the [M+H]+ spectrum were therefore examined. Positive ion MS3 spectra obtained in the ion trap from the gamma-glutamate cleavage products of FOG7 and its derivative (d7-FOG7) afforded an abundant ion not observed in spectra generated from the cysteinyl leukotrienes. Formation of this fragment ion likely occurred via a McLafferty-type rearrangement to afford cleavage of the C6-C7 bond adjacent to the sulfur atom and was valuable for the identification of the structure of FOG7 and defining the biosynthetic pathway as a 1,4-Michael addition of glutathione to 5-oxo-eicosatetraenoic acid (5-oxo-ETE).     

Structural analysis of 2,6-[bis(alkyloxy)methyl]-phenyltin derivatives using electrospray ionization mass spectrometry

Electrospray ionization (ESI) mass spectrometry was applied to the structural analysis of 23 2,6-[bis(alkyloxy)methyl]phenyltin(IV) derivatives. The mass spectra were measured in both polarity modes and multistage tandem mass spectrometric (MS(n)) measurements were performed on the ion trap analyser for positively charged tin-containing ions. The sum of complementary ions observed in the positive-ion mode (i.e. [M-R(3)](+) ion) and in the negative-ion mode (i.e. [R(3)](-) ion) permits molecular mass determination in spite of the fact that the molecular adducts were often missing even in the first-order mass spectra. The subsequent fragmentation of [M-R(3)](+) ions studied by MS(n) and the correlation of observed fragment ions with the expected structures of synthesized organotin(IV) compounds allowed us to understand the fragmentation behaviour and the mechanism of the ion formation for studied compounds. The typical neutral losses are alkenes, alcohols and aldehydes. The fragmentation pattern of one selected compound was supported by MS(n) measurements of an isotopically labelled analogue to confirm unusual ion-molecule reactions of some fragment ions with water in the ion trap.     

Comparison of negative and positive ion electrospray tandem mass spectrometry for the liquid chromatography tandem mass spectrometry analysis of oxidized deoxynucleosides

Oxidized deoxynucleosides are widely used as biomarkers for DNA oxidation and oxidative stress assessment. Although gas chromatography mass spectrometry is widely used for the measurement of multiple DNA lesions, this approach requires complex sample preparation contributing to possible artifactual oxidation. To address these issues, a high performance liquid chromatography (HPLC)-tandem mass spectrometric (LC-MS/MS) method was developed to measure 8-hydroxy-2'-deoxyguanosine (8-OH-dG), 8-hydroxy-2'-deoxyadenosine (8-OH-dA), 2-hydroxy-2'-deoxyadenosine (2-OH-dA), thymidine glycol (TG), and 5-hydroxy-methyl-2'-deoxyuridine (HMDU) in DNA samples with fast sample preparation. In order to selectively monitor the product ions of these precursors with optimum sensitivity for use during quantitative LC-MS/MS analysis, unique and abundant fragment ions had to be identified during MS/MS with collision-induced dissociation (CID). Positive and negative ion electrospray tandem mass spectra with CID were compared for the analysis of these five oxidized deoxynucleosides. The most abundant fragment ions were usually formed by cleavage of the glycosidic bond in both positive and negative ion modes. However, in the negative ion electrospray tandem mass spectra of 8-OH-dG, 2-OH-dA, and 8-OH-dA, cleavage of two bonds within the sugar ring produced abundant S1 type ions with loss of a neutral molecule weighing 90 u, [M - H - 90]-. The signal-to-noise ratio was similar for negative and positive ion electrospray MS/MS except in the case of thymidine glycol where the signal-to-noise was 100 times greater in negative ionization mode. Therefore, negative ion electrospray tandem mass spectrometry with CID would be preferred to positive ion mode for the analysis of sets of oxidized deoxynucleosides that include thymidine glycol. Investigation of the fragmentation pathways indicated some new general rules for the fragmentation of negatively charged oxidized nucleosides. When purine nucleosides contain a hydroxyl group in the C8 position, an S1 type product ion will dominate the product ions due to a six-membered ring hydrogen transfer process. Finally, a new type of fragment ion formed by elimination of a neutral molecule weighing 48 (CO2H4) from the sugar moiety was observed for all three oxidized purine nucleosides.     

Tandem mass spectra of transition-metal ion adducts of glycosyl dithioacetals; distinction among stereoisomers

Electrospray ionization mass spectra of some glycosyl dithioacetals recorded in the presence of transition-metal chlorides, XCl2 (where X = Co, Mn and Zn), give abundant adduct ions such as [M+XCl]+ and [2M-H+X]+ and minor ions such as [M-H+X]+ and [2M+XCl]+. The tandem mass spectra of these adducts show characteristic elimination of neutral molecules such as H2O, HCl, EtSH, CH2O, C2H4O2/C2H4O. [M+XCl]+ ions fragment readily and the fragmentation appears to be stereochemically controlled as the relative abundances of the fragments are different for three stereoisomers. The added metal is lost as neutral molecules in the form of XCl(OH) and XCl(SEt). This is a predominant pathway in the ZnCl+ adducts. [2M+XCl]+ ions fragment preferentially by elimination of HCl, indicating strong metal interactions in the resulting dimeric [2M-H+X]+ ion. As there are several electron-rich centers in the molecule, the dimeric complex [2M-H+X]+ can have several structures and the observed fragmentations may reflect the sum of those of all these structures. The dimeric complexes fragment by elimination of neutral molecules leaving the dimeric interactions intact. The extent of fragmentation varies for the stereoisomers, leading to stereochemical differentiation.     

Fragmentation studies on monensin A and B by accurate-mass electrospray tandem mass spectrometry

Monensin A and B were studied by electrospray ionisation tandem mass spectrometry (ESI-MS/MS) and the fragment ions were confirmed by accurate-mass measurements. Analyses were performed on both a quadrupole time-of-flight (QTOF) and a Fourier-transform ion cyclotron resonance (FTICR) mass spectrometer. The analysis revealed that fragment ions were produced by Grob-Wharton fragmentations and pericyclic rearrangements in addition to various simple neutral losses. A study of the protonated and sodiated sodium salt revealed different fragmentation pathways for these species, thus complementary structural information could be gained. A complete fragmentation pathway of monensin A and B protonated sodium salt [(M-H+Na)+H])+) and sodiated sodium salt [(M-H+Na)+Na](+) is proposed. MS(3) analysis confirmed the separate fragmentation pathways.     

An unexpected ion-molecule adduct in negative-ion collision-induced decomposition ion-trap mass spectra of halogenated benzoic acids

The ion observed at m/z 145 when product ion spectra of iodobenzoate anions are recorded using ion-trap mass spectrometers corresponds to the adduct ion [I(H(2)O)](-). The elements of water required for the formation of this adduct do not originate from the precursor ion but from traces of moisture present in the helium buffer gas. A collision-induced decomposition (CID) spectrum recorded from the [M-H](-) ion (m/z 251) derived from 3-iodo[2,4,5,6-(2)H(4)]benzoic acid also showed an ion at m/z 145. This observation confirmed that the m/z 145 is not a product ion resulting from a direct neutral loss from the carboxylate anion. (79)Bromobenzoate anions produce similar results showing an ion at m/z 97 for [(79)Br(H(2)O)](-). The ion-molecule reaction observed here is unique to ion-trap mass spectrometers since a corresponding ion was not observed under our experimental conditions in spectra recorded with in-space tandem mass spectrometers such as triple quadrupole or quadrupole time-of-flight instruments.     

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.     

Studies of iridoid glycosides using liquid chromatography/electrospray ionization tandem mass spectrometry

Fragmentation pathways of five iridoid glycosides have been studied by using electrospray ionization multi-stage tandem mass spectrometry (ESI-MS(n)). The first-stage MS data of the five iridoid glycosides were compared. The MS spectra showed that the adduct ions of iridoid glycosides and the formate anion were diagnostic ions to distinguish iridoid glycosides with a carboxyl group at the C-4 position or an ester group at the C-4 position. The MS fragmentation pathways of the five iridoid glycosides were also studied. Analyzing the product ion spectra of iridoid glycosides, some neutral losses were observed, such as H(2)O, CO(2) and glucose residues, which were very useful for the identification of the functional groups in the structures of iridoid glycosides. Furthermore, specific loss of one molecule of methyl 3-oxopropanoate or 3-oxopropanic acid was firstly discussed, which corresponded to the isomerization of the hemiacetal group in the structure of iridoid aglycone. According to the fragmentation mechanisms and HPLC/MS(n) data, the structures of five iridoid glycosides in a crude extract of Gardenia jasminoisdes fruit have been identified. Three compounds were compared with standards and the other two were identified as shanzhiside and genipin gentibioside by their MS(n) data without standard compounds. In order to further validate the veracity of the deduction, genipin gentiobioside was isolated from the extract of Gardenia jasminoisdes fruit using Purification Factory and was further identified by C- and H-NMR.     

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.