Electrospray and atmospheric pressure chemical ionization tandem mass spectrometric behavior of eight anabolic steroid glucuronides

Mass spectrometric and tandem mass spectrometric behavior of eight anabolic steroid glucuronides were examined using electrospray (ESI) and atmospheric pressure chemical ionization (APCI) in negative and positive ion mode. The objective was to elucidate the most suitable ionization method to produce intense structure specific product ions and to examine the possibilities of distinguishing between isomeric steroid glucuronides. The analytes were glucuronide conjugates of testosterone (TG), epitestosterone (ETG), nandrolone (NG), androsterone (AG), 5alpha-estran-3alpha-ol-17-one (5alpha-NG), 5beta-estran-3alpha-ol-17-one (5beta-NG), 17alpha-methyl-5alpha-androstane-3alpha,17beta-diol (5alpha-MTG), and 17alpha-methyl-5beta-androstane-3alpha,17beta-diol (5beta-MTG), the last four being new compounds synthesized with enzyme-assisted method in our laboratory. High proton affinity of the 4-ene-3-one system in the steroid structure favored the formation of protonated molecule [M + H]+ in positive ion mode mass spectrometry (MS), whereas the steroid glucuronides with lower proton affinities were detected mainly as ammonium adducts [M + NH4]+. The only ion produced in negative ion mode mass spectrometry was a very intense and stable deprotonated molecule [M - H]- . Positive ion ESI and APCI MS/MS spectra showed abundant and structure specific product ions [M + H - Glu]+, [M + H - Glu - H2O]+, and [M + H - Glu - 2H2O]+ of protonated molecules and corresponding ions of the ammonium adduct ions. The ratio of the relative abundances of these ions and the stability of the precursor ion provided distinction of 5alpha-NG and 5beta-NG isomers and TG and ETG isomers. Corresponding diagnostic ions were only minor peaks in negative ion MS/MS spectra. It was shown that positive ion ESI MS/MS is the most promising method for further development of LC-MS methods for anabolic steroid glucuronides.     

Rapid and selective identification of molecular species in phosphatidylcholine and sphingomyelin by conditional neutral loss scanning and MS3

Analyses of molecular species of phospholipids containing choline (Ch), such as phosphatidylcholine (PC) and sphingomyelin (SM), are reported. Neutral loss scanning was applied for the selective detection of these lipids using a quadrupole-linear ion trap mass spectrometer. By using ammonium formate as an elution buffer, both PC and SM were detected as [M+HCOO]- ions in the negative ion mode. Upon collisional activation, the [M+HCOO]- adduct ions underwent facile elimination of HCO2, to yield an ion which, in turn, readily underwent collisional-induced dissociation (CID) to eliminate CH3 to yield an [M-CH3]- ion. By selecting the proper conditions for scanning for neutral loss of 60 Da (HCO2+CH3), SM species were identified separately from PCs. Further, by selection of this [M-CH3]- ion as the precursor ion, the identities of the fatty acyl chains of PC species can be effectively obtained by MS3 experiments. Furthermore, by the MS3 analyses of [M-CH3]- specifically obtained from SM molecules, identification of sphingosine or sphinganine derivatives and their N-acyl species can also be effectively obtained. This systematic analysis of PCs and SMs by conditional neutral loss scanning, with subsequent analyses by MS3, using a linear ion trap mass spectrometer in the negative ion mode, appears to be a very effective and sensitive method. Further, MS/MS in the positive ion mode at relatively low collision energy was also effective for the identification of positional specificities in individual molecular PC species from their lysoPC-related fragments. The present paper deals only with qualitative identification of individual molecular species, and the related quantitative studies are now underway.     

Characterization of moenomycin antibiotics from medicated chicken feed by ion-trap mass spectrometry with electrospray ionization

The antimicrobial moenomycin, commonly used as a growth promoter in livestock, was isolated from medicated chicken feed. The purified extract was subjected to reversed-phase liquid chromatographic separation followed by structural characterization using ion-trap mass spectrometry (ITMS), which allowed identification of five moenomycins (A, A12, C1, C3, and C4) as the major components. The fragmentation patterns of the protonated and deprotonated moenomycin molecules, as well as of a series of sodium adducts, were investigated using ITMS after electrospray ionization. While the protonated molecules [M+H]+ proved highly unstable and underwent extensive in-source fragmentation, isolation and activation of the [M--H]- ions (m/z 1580 for moenomycin-A) yielded simple mass spectra with a dominant base peak corresponding to the loss of the carboxy-glycol and the C25-hydrocarbon chain (m/z 1152 for moenomycin-A). Further study of this fragment ion in an MS3 experiment gave rise to a peculiar product ion (m/z 902 for moenomycin-A) that was attributed to the expulsion of a carbohydrate moiety representing a central building block of the linear molecule. In positive ion mode the generation of the mono-sodiated adduct ions, [M+Na]+, was promoted by amending the mobile phase with 100 microM sodium acetate, but this also resulted in higher adducts of the type [M+2Na--H]+ and [M+3Na--2H]+ arising from the formation of the sodium salts of the phosphate acid diester and subsequently of the carboxylic acid. Substantial differences among the fragment-rich product ion profiles of the three species were observed, and could in part be traced back to the mode of complexation of the additional sodium cation(s).     

Quantification of monosaccharides through multiple‐reaction monitoring liquid chromatography/mass spectrometry using an aminopropyl column

A simple, sensitive, and reproducible quantitative liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was designed for the simultaneous quantification of monosaccharides derived from glycoprotein and blood serum using a multiple‐reaction monitoring (MRM) approach. Sialic acids and neutral monosaccharides were efficiently separated using an amino‐bonded silica phase column. Neutral monosaccharide molecules were detected as their aldol acetate anion adducts [M + CH₃CO₂]^? using electrospray ionization in negative ion MRM mode, while sialic acids were detected as deprotonated ions [M–H]^?. The new method did not require a reduction step, and exhibited very high sensitivity to carbohydrates with limits of detection of 1 pg for the sugars studied. The linearity of the described approach spanned over three orders of magnitude (pg to ng). The method was validated for monosaccharides originating from N‐linked glycans attached to glycoproteins and glycoproteins found in human blood serum. The method effectively quantified monosaccharides originating from as little as 1 µg of glycoprotein and 5 µL of blood serum. The method was robust, reproducible, and highly sensitive. It did not require reduction, derivatization or postcolumn addition of reagents. Copyright © 2010 John Wiley & Sons, Ltd.     

Mass spectrometric and tandem mass spectrometric behavior of nitrocatechol glucuronides: A comparison of atmospheric pressure chemical ionization and electrospray ionization

The mass spectrometric (MS) and tandem mass spectrometric (MS/MS) behavior of six nitrocatechol-type glucuronides using atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) was systematically studied, and the effect of operation parameters on the fragmentations are presented. The positive ion APCI- and ESI-MS spectra showed an intense protonated molecule and the respective negative ion spectra a deprotonated molecule with minimal fragmentation. The main fragment ions in the MS/MS spectra of the protonated and deprotonated molecules were [M + H - Glu]+ and [M - H - Glu]-, respectively, formed by the loss of the glucuronide moiety. The measured limits of detection indicated that ESI is a significantly more efficient ionization method than APCI in the negative and positive ion modes for the compounds studied. MS/MS was found to be less sensitive, but more reliable and simple than MS due to the absence of chemical noise.     

Poly(ethylene glycol) doubly and singly cationized by different alkali metal ions: Relative cation affinities and cation-dependent resolution in a quadrupole ion trap mass spectrometer

Structural information of gas phase complexes of poly(ethylene glycol) (PEG) cationized by one or two different alkali metal ions is inferred from MS and MS/MS experiments performed with an electrospray quadrupole ion trap mass spectrometer. The rationale for selecting PEG was that its sites for cation binding are non-selective with respect to the repeating monomeric unit of the polymer, but there is selectivity with respect to the formation of an inner coordination sphere specific to each metal ion. The dissociation of [M1+ M2+ (EO23)], where EO23 = linear polymer of ethylene oxide, 23 units in length, resulted in loss of one of the alkali metal ions, with preference for loss of the larger cation, with no fragmentation of the PEG backbone for Na, K, Rb, and Cs. Li was not examined in this portion of the study. The selectivity for loss of the larger alkali metal ion was [Na+ K+ (EO23)] to [Na+ (EO23)] + K+ at 100%; [K+ Rb+ (EO23)] to [K+ (EO23)] + Rb+ at 93%; and [Rb+ Cs+ (EO23)] to [Rb+ (Eo23)] + Cs+ at 99%. The resolution of [M+ (EOx)] for x = 20-30 was dependent on the alkali metal ion, with the highest resolution observed for Cs+ and the lowest for Na+. These results are discussed with respect to the packing of the oxygen atoms on PEG (M.W.(avg) = 1000) around an alkali metal ion of different radius, and how this packing leads to an ensemble of unique structures, and therefore mobilities for [M+ (EOx)].     

Characterization of the chemical components on the surface of different solids with electrospray-assisted laser desorption ionization mass spectrometry

In this study we demonstrate that electrospray-assisted laser desorption ionization (ELDI) mass spectrometry (MS) can be used to rapidly characterize major chemical components on the surfaces of different solids under ambient conditions. The major chemical components in (a) dried milks with different fat contents, (b) different color-regions of a painting, (c) the thin coating on a compact disc, (d) drug tablets, and (e) porcine brain tissue were rapidly characterized as protonated molecules [M+H](+) or sodiated molecules [M+Na](+) by ELDI-MS with minimum sample pretreatment. The ionized ions of synthetic polymer and dye standards were detected directly from dried sample solutions using either positive or negative ion mode. Further structural information for the FD&C Red dye was obtained through tandem mass spectrometric (MS/MS) analysis using an ion trap mass analyzer attached to the ELDI source.     

Enhancement of atmospheric pressure chemical ionization for the determination of free and glycine-conjugated bile acids in human serum

A highly sensitive and accurate method based on the precolumn derivatization of bile acids (BA) with a high ionization efficiency labeling reagent 1,2-benzo-3,4-dihydrocarbazole-9-ethyl-benzenesulfonate (BDEBS) coupled with LC/MS has been developed. After derivatization, BA molecules introduced a weak basic nitrogen atom into the molecular core structure that was readily ionized in commonly used acidic HPLC mobile phases. Derivatives were sufficiently stable to be efficiently analyzed by atmospheric pressure chemical ionization (APCI)-MS/MS in positive-ion mode. The MS/MS spectra of BA derivatives showed an intense protonated molecular ion at m/z [M + H]+. The collision-induced dissociation of the molecular ion produced fragment ions at [MH-H2O]+, [MH-2H2O]+, [MH-3H2O]+. The characteristic fragment ions were at m/z 320.8, 262.8, and 243.7 corresponding to a cleavage of N-CO, O-CO, and C-OCO, respectively, and bonds of derivatized molecules. The selected reaction monitoring, based on the m/z [M+H]+ --> [MH-H2O]+, [MH-2H2O]+, [MH-3H2O]+, 320.8, 262.8, and 243.7 transitions, was highly specific for the BA derivatives. The LODs for APCI in a positive-ion mode, at an S/N of 5, were 44.36-153.6 fmol. The validation results showed high accuracy in the range of 93-107% and the mean interday precision for all standards was <15% at broad linear dynamic ranges (0.0244-25 nmol/mL). Good linear responses were observed with coefficients of > 0.9935 in APCI/MS detection. Therefore, the facile BDEBS derivatization coupled with mass spectrometric analysis allowed the development of a highly sensitive and specific method for the quantitation of trace levels of the free and glycine-conjugated BA from human serum samples.     

Pharmacokinetic studies of soyalkaloid A from Portulaca oleracea L. using ultra high‐performance liquid chromatography electrospray ionization quadrupole–time of flight mass spectrometry and its antioxidant activity

Soyalkaloid A was isolated from Portulaca oleracea L. for the first time in our laboratory and then a rapid and sensitive ultra‐high‐performance liquid chromatography electrospray ionization quadrupole–time of flight mass spectrometry (UHPLC–ESI–Q–TOF/MS) method with hesperidin as internal standard (IS) was developed and validated to investigate the pharmacokinetics of soyalkaloid A in rats after oral and intravenous administrations. The analysis was achieved on an Agilent Zorbax Eclipse Plus C₁₈ Column (2.1 × 50 mm, 1.8 μm) by elution with acetonitrile and water (containing 0.1% formic acid), at a flow rate of 0.3 mL/min. The MS analysis was performed in the positive ion mode with monitored ion m/z 227.0814 [M + H]⁺ and 611.1971 [M + H]⁺ for soyalkaloid A and IS, respectively. The linear range was established over the concentration range 7.5–6000 ng/mL (r = 0.9951). The intra‐ and inter‐assay accuracy and precision were between ?4.86‐4.49 and 1.93–9.66, respectively. The lower limits of detection and quantitation observed were 2.1 and 7.4 ng/mL, respectively. The rapid, sensitive and specific UHPLC–ESI–Q–TOF/MS method was successfully applied to a pharmacokinetic study of soyalkaloid A. Moreover, its antioxidant was studied via a 1,1‐diphenyl‐2‐picryl‐hydrazyl radical scavenging assay, the IC₅₀ value being 20.73 ± 0.51 μM.     

Negative ion production from peptides and proteins by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Negative ion production from peptides and proteins was investigated by matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. Although most research on peptide and protein identification with ionization by MALDI has involved the detection of positive ions, for some acidic peptides protonated molecules are not easily formed because the side chains of acidic residues are more likely to lose a proton and form a deprotonated species. After investigating more than 30 peptides and proteins in both positive and negative ion modes, [M–H]⁻ ions were detected in the negative ion mode for all peptides and proteins although the matrix used was 2,5‐dihydroxybenzoic acid (DHB), which is a good proton donor and favors the positive ion mode production of [M+H]⁺ ions. Even for highly basic peptides without an acidic site, such as myosin kinase inhibiting peptide and substance P, good negative ion signals were observed. Conversely, gastrin I (1‐14), a peptide without a highly basic site, will form positive ions. In addition, spectra obtained in the negative ion mode are usually cleaner due to absence of alkali metal adducts. This can be useful during precursor ion isolation for MS/MS studies. Copyright © 2008 John Wiley & Sons, Ltd.     

Spontaneous N --> O acyl shift in the [M + H](+) ions of [MeBmt1]-cyclosporins in an ion trap.

In an ion trap the protonated molecules of the cyclic undecapeptides cyclosporins having 3-hydroxy-4-methyl-2-methylamino-6-octenoic acid (MeBmt) in their backbone undergo an N --> O peptidyl shift into the corresponding [M + H](+) ions of isocyclosporins. This rearrangement does not take place in cyclosporins [Bmt1]Cs and [3'-deoxy-MeBmt1]Cs. In cyclosporin [Thr2]Cs having two threonines in the molecule, only one of them participates in the N,O-acyl transfer. It can be concluded that the presence of the basic N-methylamino group of MeBmt, which can serve as the primary site of protonation, is necessary for isocyclosporin formation. A dominating ion series originating from the primary cleavage between MeBmt (first position in the cyclosporin ring) and amino acid residue at the neighbouring eleventh position is then observed in collision-induced dissociation spectra of protonated molecules of cyclosporins. This 'isocyclosporin' ion series can effectively be used for easy and complete cyclosporin sequencing using a tandem mass spectrometric (MS3) experiment in an ion trap. The paper further introduces an improved Gross mass spectral nomenclature for cyclic peptide sequencing and several techniques for the generation of protonated molecules of cyclosporins. Their preparation represents the fundamental requirement for smooth sequencing of cyclosporins by tandem mass spectral techniques.     

Structural characterization of 2-aminobenzamide-derivatized oligosaccharides using a matrix-assisted laser desorption/ionization two-stage time-of-flight tandem mass spectrometer

Oligosaccharides were derivatized by reductive amination using 2-aminobenzamide (2-AB) and analyzed by matrix-assisted laser desorption/ionization two-stage time-of-flight (MALDI-TOF/TOF) tandem mass spectrometry (MS/MS) in the positive ion mode. The major signals were obtained under these conditions from the [M+Na]+ ions for all 2-AB-derivatized oligosaccharides. A systematic study was conducted on a series of 2-AB-derivatized oligosaccharides to allow rationalization of the fragmentation processes. The MALDI-TOF/TOF-MS/MS spectra of the [M+Na]+ ions of 2-AB-derivatized oligosaccharides were dominated by glycosidic cleavages. These fragments originating both from the reducing and the non-reducing ends of the oligosaccharide yield information on sequence and branching. Moreover, the MALDI-TOF/TOF-MS/MS spectra were also characterized by abundant cross-ring fragments which are very informative on the linkages of the monosaccharide residues constituting these oligosaccharides. MALDI-TOF/TOF-MS/MS analysis of 2-AB-derivatized oligosaccharides, by providing structural information at the low-picomole level, appears to be a powerful tool for carbohydrate structural analysis.     

Analysis of neutral oligosaccharides for structural characterization by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry

We have acquired multi-stage mass spectra (MSn) of four branched N-glycans derived from human serum IgG by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry (MALDI-QIT-TOF-MS) in order to demonstrate high sensitivity structural analysis. [M+H]+ and [M+Na]+ ions were detected in the positive mode. The detection limit of [M+Na]+ in MS/MS and MS3 measurements for structural analysis was found to be 100 fmol, better than that for [M+H]+. The [M+H]+ ions subsequently fragmented to produce predominantly a Y series of fragments, whereas [M+Na]+ ions fragmented to give a complex mixture of B and Y ions together with some cross-ring fragments. Three features of MALDI-QIT-CID fragmentation of [M+Na]+ were cleared by the analysis of MS/MS, MS3 and MS4 spectra: (1) the fragment ions resulting from the breaking of a bond are more easily generated than that from multi-bond dissociation; (2) the trimannosyl-chitobiose core is either hardly dissociated, easily ionized or it is easy to break a bond between N-acetylglucosamine and mannose; (3) the fragmentation by loss of only galactose from the non-reducing terminus is not observed. We could determine the existence ratios of candidates for each fragment ion in the MS/MS spectrum of [M+Na]+ by considering these features. These results indicate that MSn analysis of [M+Na]+ ions is more useful for the analysis of complicated oligosaccharide structures than MS/MS analysis of [M+H]+, owing to the higher sensitivity and enhanced structural information. Furthermore, two kinds of glycans, with differing branch structures, could be distinguished by comparing the relative fragment ion abundances in the MS3 spectrum of [M+Na]+. These analyses demonstrate that the MSn technology incorporated in MALDI-QIT-TOF-MS can facilitate the elucidation of structure of complex branched oligosaccharides.     

Direct analysis in real time mass spectrometry (DART‐MS) of highly non‐polar low molecular weight polyisobutylenes

Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end‐groups were studied using direct analysis in real time mass spectrometry (DART‐MS). To facilitate the adduct ion formation under DART conditions, NH₄Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]^? up to m/z 1100, and the deprotonated polyisobutylene succinic acid [M? H]^? were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH₄]⁺, adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]^?, product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]^? into a Cl^? ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH₄]⁺ ions, allowing us to obtain valuable information on the arm‐length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART‐MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural determination of the novel fragmentation routes of zwitteronic morphine opiate antagonists naloxonazine and naloxone hydrochlorides using electrospray ionization tandem mass spectrometry

Electrospray ionization quadrupole time-of-flight (ESI-QqToF) mass spectra of the zwitteronic salts naloxonazine dihydrochloride 1 and naloxone hydrochloride 2, a common series of morphine opiate receptor antagonists, were recorded using different declustering potentials. The singly charged ion [M+H-2HCl](+) at m/z 651.3170 and the doubly charged ion [M+2H-2HCl](2+) at m/z 326.1700 were noted for naloxonazine dihydrochloride 1; and the singly charged ion [M+H-HCl](+) at m/z 328.1541 was observed for naloxone hydrochloride 2. Low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) experiments established the fragmentation routes of these compounds. In addition to the characteristic diagnostic product ions obtained, we noticed the formation of a series of radical product ions for the zwitteronic compounds 1 and 2, and also the formation of a distonic ion product formed from the singly charged ion [M+H-HCl](+) of naloxone hydrochloride 2. Confirmation of the various established fragmentation routes was effected by conducting a series of ESI-CID-QqTof-MS/MS product ion scans, which were initiated by CID in the atmospheric pressure/vacuum interface using a higher declustering potential. Deuterium labeling was also performed on the zwitteronic salts 1 and 2, in which the hydrogen atoms of the OH and NH groups were exchanged with deuterium atoms. Low-energy CID-QqTof-MS/MS product ion scans of the singly charged and doubly charged deuteriated molecules confirmed the initial fragmentation patterns proposed for the protonated molecules. Precursor ion scan analyses were also performed with a conventional quadrupole-hexapole-quadrupole tandem mass spectrometer and allowed the confirmation of the genesis of some diagnostic ions.     

Ionisation and fragmentation of complex glycans with a quadrupole time-of-flight mass spectrometer fitted with a matrix-assisted laser desorption/ionisation ion source

This paper reports the use of an experimental matrix-assisted laser desorption/ionisation (MALDI) ion source fitted to a quadrupole time-of-flight (Q-Tof) mass spectrometer for the analysis of carbohydrates, particularly the N-linked glycans from glycoproteins. Earlier work on the Q-Tof instrument, using electrospray ionisation, gave excellent MS/MS spectra, particularly from the [M + Na]+ ions, but suffered from the major disadvantages that the signal was often split between singly and multiply charged ions and that sensitivity fell dramatically as the molecular weight of the carbohydrate rose. The MALDI ion source did not suffer from these problems and the instrument produced excellent MS and MS/MS spectra from small amounts of complex, underivatised glycans as well as those derivatised at the reducing terminus. Positive ion MS spectra of sialylated glycans recorded on the new instrument were much less complex than those recorded with a conventional MALDI-TOF instrument because of the absence of ions resulting from metastable (post-source decay, (PSD)) fragmentations occurring in the flight tube. However, considerable fragmentation by loss of sialic acid still occurred. MS/MS spectra of the [M + Na]+ ions from all compounds were almost identical to those recorded earlier with the electrospray-Q-Tof combination and far superior to MALDI-PSD spectra recorded with reflectron-TOF instruments. Spectra are shown for neutral and sialylated N-linked glycans from chicken ovalbumin, riboflavin binding protein, alpha1-acid glycoprotein, bovine fetuin and ribonuclease B, both as free glycans and as those derivatised at their reducing termini. The technique was applied to the structural determination of N-linked glycans from human secretory IgA and Apo-B 100 from human low-density lipoprotein.     

Development of a method for simultaneous determination of eflucimibe and its three major metabolites in rat plasma by liquid chromatography/electrospray tandem mass spectrometry: a preliminary study

A high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry (HPLC/ESI-MS/MS) method has been developed for the simultaneous determination of eflucimibe, a powerful acyl-coenzyme A cholesterol O-acyltransferase (ACAT) inhibitor, and its main metabolites, in plasma. The ESI and MS/MS parameters were investigated and optimised for each of the four compounds in the positive ion mode. Plasma samples were deproteinised by precipitation with acetonitrile and directly analysed by HPLC/ESI-MS/MS in less than 4 min. Quantitation was performed in the multiple reaction monitoring (MRM) mode for highest sensitivity, selecting the protonated molecules [M+H](+) as precursor ions. The method was demonstrated to be specific and sensitive, and a linear response was observed within a 1-25 ng/mL concentration range. Correlation coefficients (r(2)) greater than 0.9960 were obtained by least-squares regression, and limits of detection down to 0.2 ng/mL were calculated. Therefore, this HPLC/ESI-MS/MS method appears to be an efficient tool, able to provide valuable information for a pharmacological purpose.     

Investigation of the electrochemical oxidation products of zotepine and their fragmentation using on-line electrochemistry/electrospray ionization mass spectrometry

When zotepine, an antipsychotic drug, was electrochemically oxidized using electrospray ionization mass spectrometry (ESI-MS) coupled with a microflow electrolytic cell, [M + 16 + H]+ (m/z 348), [M-H]+ (m/z 330) and [M-14 + H]+ (m/z 318) were observed as electrochemical oxidation product ions (M represents the zotepine molecule). Although a major fragment ion that was derived from the dimethyl aminoethyl moiety was observed only at m/z 72 in the collision-induced dissociation (CID) spectrum of zotepine, new fragments such as m/z 315 and 286 ions could be generated in the CID spectrum by combining electrochemical oxidation and CID. Since these fragments were relatively specific with high ion strength, it was thought that they would be useful for developing a sensitive LC-MS/MS assay. The S-oxide and N-demethylated products were detected by electrolysis assuring that a portion of P450 metabolites of zotepine could be mimicked by the electrochemistry/electrospray ionization mass spectrometry (EC/ESI-MS) system.     

Determination of antibiotics in aquatic environment by solid-phase extraction followed by liquid chromatography-electrospray ionization mass spectrometry

A robust and sensitive solid-phase extraction followed by liquid chromatography-electrospray ionization mass spectrometric (LC-ESI-MS) method for determination of antibiotics viz., fluoroquinolones, sulfamethoxazole, trimethoprim and cephalosporines in surface waters was developed. The sample recoveries on Oasis HLB cartridges were found to be >80%. Identification was carried out by LC-ESI-MS/MS. The positive ion ESI mass spectra containing the peaks of quasimolecular ions [M+H](+) allowed the determination of molecular masses whereas the fragment ions obtained by MS/MS of [M+H](+) ions permitted the structural assignment. Quantification was carried out by selective ion monitoring (SIM) using the quasimolecular ions [M+H](+) of the parent compounds. The detection and quantification limits were found to be in the range of 0.6-8.1 and 2.0-24.0 microg/L. The surface waters of different lakes and tanks of Hyderabad, India were found to contain a few antibiotics.     

单糖衍生物的电喷雾质谱裂解规律研究

以1-(2-萘基)-3-甲基-5-吡唑啉酮(NMP)作单糖标识剂, 经在线串联的LC-ESI-MS建立了单糖衍生物的电喷雾质谱裂解方法.衍生物在质谱裂解中糖类化合物特有的规范信息.借助糖类化合物在ESI-MS条件下表现出的分子离子峰m/z [M H] , 及在ESI-MS/MS条件下呈现出的特征碎片离子峰m/z 473, 可有效地确定出单糖类化合物的组成. 尽管一些脂肪醛和芳香醛也能同时被标识, 然而在质谱条件下不产生m/z 473的特征碎片离子峰, 且它们的洗脱远在糖类组分之后, 因此不干扰糖类化合物的分离和结构确定.通过建立的LC-ESI-MS方法, 对水解蜂花粉中的单糖进行了分析.结果表明: 水解的蜂花粉中含甘露糖(Man)、半乳糖醛酸(GalUA)、葡萄糖醛酸(GlcUA)、鼠李糖(Rha)、葡萄糖 (Glc)、半乳糖(Gal)、阿拉伯糖(Ara)、木糖(Xyl)和岩藻糖(Fuc).本方法为环境样品中单糖类化合物的确定提供了准确、可靠的技术手段.