Metabolite identification of arbidol in human urine by the study of CID fragmentation pathways using HPLC coupled with ion trap mass spectrometry

The metabolism of arbidol in humans was studied using liquid chromatography-electrospray ionization (ESI) ion trap mass spectrometry (ITMS) after an oral dose of 300-mg arbidol. A total of 17 metabolites were identified including the glucuronide arbidol and the glucuronide sulfinylarbidol as the major metabolites.Arbidol and its metabolites have some common fragmentation patterns as a result of a homolytic bond cleavage. This cleavage will form odd-electron ions with the loss of a radical. The arbidol fragmentation sequence is first to lose dimethylamine (45 Da), followed by the loss of acetaldehyde (44 Da), and then the phenylthio radical (109 Da). This fragmentation sequence is also observed from N-demethylarbidol, sulfonylarbidol, and N-demethylsulfonylarbidol. However, for sulfinylarbidol and N-demethylsulfinylarbidol, the fragmentation sequence is reversed so that the phenylsulfiny radical (125 Da) was lost first, followed by the loss of dimethylamine (45 Da), and then acetaldehyde (44 Da). The exact masses for arbidol and sulfinylarbidol fragment ions were determined by a quadrupole/time-of-flight mass spectrometer (Q-TOF MS).The phase II metabolites, such as sulfate and glucuronide conjugates of arbidol, N-demethylarbidol, sulfonylarbidol, and N-demethylsulfonylarbidol were identified by observing the neutral loss of 80 Da (SO(3)) or 176 Da (glucuronic acid) from the MS(2) spectra. The sulfate and glucuronide conjugates such as sulfinylarbidol and N-demethylsulfinylarbidol had an unusual fragmentation pattern, in which the phenylsulfinyl radical (125 Da) was lost before the loss of SO(3) group (80 Da) or glucuronic acid (176 Da) occurred.     

Experimental design optimization of the capillary electrophoresis separation of leucine enkephalin and its immune complex

To optimize the capillary electrophoretic separation conditions for leucine enkephalin (LE) and the immune complex of the LE and anti-LE reaction, an analysis using a three-level, three-factorial Box-Behnken design was performed. Three separation parameters, buffer pH (X(1)), buffer concentration (X(2)), and applied voltage (X(3)), were chosen to observe the effect on separation responses. The responses were theoretical plate number, migration time of the LE peak, and resolution between the peaks. The optimum conditions and process validation were determined using statistical regression analysis and surface plot diagrams. The capillary electrophoresis optimum separation conditions were established to be 75 mM phosphate buffer at pH 7.00 with an applied separation voltage of 15 kV. By using the analysis technique, the prediction of responses was satisfactory and process verification yielded values within the +/-5% range of the predicted efficiency.     

CID of singly charged antioxidants applied in lubricants by means of a 3D ion trap and a linear ion trap-Orbitrap mass spectrometer

The aim of this study was to investigate the fragmentation behavior induced by low‐energy collision‐induced dissociation (LE‐CID) of four selected antioxidants applied in lubricants, by two different types of ion trap mass spectrometers: a three‐dimensional ion trap (3D‐IT) and a linear IT (LIT) Orbitrap MS. Two sterically hindered phenols and two aromatic amines were selected as model compounds representing different antioxidant classes and were characterized by positive‐ion electrospray ionization (ESI) and LE‐CID. Various types of molecular ions (e.g. [M]^+?, [M + H]⁺, [M + NH₄]⁺ or [M + Na]⁺) were used as precursor ions generating a significant number of structurally relevant product ions. Furthermore, the phenolic compounds were analyzed by negative‐ion ESI. For both IT types applied for fragmentation, the antioxidants exhibited the same unusual LE‐CID behavior: (1) they formed stable radical product ions and (2) C? C bond cleavages of aliphatic substituents were observed and their respective cleavage sites depended on the precursor ion selected. This fragmentation provided information on the type of structural isomer usually not obtainable for branched aliphatic substituents utilizing LE‐CID. Comparing the two instruments, the main benefit of applying the LIT‐Orbitrap was direct access to elemental composition of product ions enabling unambiguous interpretation of fragmentation trees not obtainable by the 3D‐IT device (e.g. loss of isobaric neutrals). It should be emphasized that the types of product ions formed do not depend on the type of IT analyzer applied. For characterizing degradation products of antioxidants, the LIT‐Orbitrap hybrid system, allowing the determination of accurate m/z values for product ions, is the method of choice. Copyright © 2011 John Wiley & Sons, Ltd.     

Identification of primary and sequential bioactivation pathways of carbamazepine in human liver microsomes using liquid chromatography/tandem mass spectrometry

Carbamazepine (CBZ)-induced idiosyncratic toxicities are commonly believed to be related to the formation of reactive metabolites. CBZ is metabolized primarily into carbamazepine-10,11-epoxide (CBZE), 2-hydroxycarbamazepine (2-OHCBZ) and 3-hydroxycarbamazepine (3-OHCBZ), in human liver microsomes (HLM). Over the past two decades, the 2,3-arene oxidation has been commonly assumed to be the major bioactivation pathway of CBZ. Recently, CBZE has been also confirmed to be chemically reactive. In order to identify other possible primary and sequential CBZ bioactivation pathways, individual HLM incubations of CBZ, CBZE, 2-OHCBZ and 3-OHCBZ were conducted in the presence of glutathione (GSH). In the CBZ incubation, a variety of GSH adducts were formed via individual or combined pathways of 10,11-epoxidation, arene oxidation and iminoquinone formation. In the CBZE incubation, the only detected GSH adducts were CBZE-SG1 and CBZE-SG2, which represented the two most abundant conjugates observed in the CBZ incubation. In the incubation of either 2-OHCBZ or 3-OHCBZ, a number of sequential GSH adducts were observed. However, none of the 2-OHCBZ-derived GSH adducts were detected in the CBZ incubation. Meanwhile, several GSH adducts were only observed in the CBZ incubation. In conclusion, CBZ can be bioactivated in HLM via 10,11-epoxidation, 2,3-arene oxidation, and several other pathways. In addition, the sequential bioactivation of 3-OHCBZ appeared to play a more important role than that of either CBZE or 2-OHCBZ in the overall bioactivation of CBZ in HLM. The identification of several new bioactivation pathways of CBZ in HLM demonstrates that possible CBZ bioactivation can be more complex than previously thought.     

On the effect of low-energy ion bombardment on polystyrene and polymethylmethacrylate etch rates in rf plasmas

The effect of low-energy ion bombardment on CD₄/O₂ and CF₃X (X=F, Cl, Br) plasma etching has been assessed by applying controlled rf bias voltages on polystyrene (PS) and polymethylmethacrylate (PMMA) samples. In both cases ion bombardment has been found to have a chemical effect. In the case of CF₄/O₂ discharges, ion bombardment has been found to change the relative etching efficiency of different mixtures. In the case of CF₃X plasmas, ion bombardment has been found to alter PMMA and PS etch rates in a different way. In particular, the ratios between CF₄ and CF₃X (X=Cl, Br) etch rates of PS have been found to decrease with increasing bias voltage. This effect has been tentatively attributed to an ion bombardment-induced enhancement of the reaction between the aromatic ring and halogen molecules formed in CF₃Cl and CF₃Br discharges.     

Multi-stage collisionally-activated decomposition in an ion trap for identification of sequences, structures and bn --> bn-1 fragmentation pathways of protonated cyclic peptides

Cyclic penta-, hexa- and heptapeptides have been designed, synthesized and their fragmentations induced by multistage tandem mass spectrometry have been studied. Under low-energy collisionally activated decomposition (CAD), the protonated cyclic peptides mainly dissociate via ring opening pathways and the corresponding bn --> bn-1 pathways to form several sets of b ions as oxazolone rings (and b1 ions as aziridinone rings). Through repeated observation of these b ions in multistep CAD experiments, accurate sequencing and head-to-tail ring structure of cyclic peptides can be determined. The mistaken assignments of these b ions can be avoided by this sequencing method. Semiempirical molecular orbital calculations have been utilized to provide insight into the proposed dissociation mechanism. In addition, for cyclic peptides that include an Asn residue, the nitrogen of the Asn side chain is observed to be preferentially protonated, which can induce a unique ring-opening pathway with a loss of ammonia that competes with the conventional ring opening pathway.     

Effects of sequential replacement of -NH2 by -OH in the tripodal tetraamine tren on its acidity and metal ion coordinating properties

The preparation is described of two modified derivatives of the tripodal tetraamine tren, 2-hydroxy-N,N-bis(2-aminoethyl)ethylamine, NN(2)O222, and 2-amino-N,N-bis(2-hydroxyethyl)ethylamine, NNO(2)222, in which one and two primary amines, respectively, have been replaced with hydroxyl groups. The aqueous acid-base and metal ion (Ni2+, Cu2+, Zn2+) coordination properties of these two compounds were studied by potentiometric, spectrophotometric, and NMR titrations. Two and three acidity constants, respectively, were determined for NNO(2)222 and NN(2)O222 by potentiometry. NMR titrations proved that deprotonation of the two OH residues in NNO(2)222, and of the one in NN(2)O222, corresponded to pK(a) > 14. Acidity constants related to deprotonation of the terminal primary amine functions were similar in both NNO(2)222 and NN(2)O222 (and to those in the parent compound tren), whereas deprotonation of the tertiary ammonium N atom had a very different acidity constant in each of these three compounds. Charge repulsion, polar effects, and intramolecular hydrogen bond formation are responsible for the discrepancy. Chelated diamine metal complexes for each ligand studied depended only on the basicity of the corresponding two amines, suggesting that the hydroxyl group interacted with the metal ion very weakly in acidic or neutral solutions. The ML2+ species further deprotonated to form M(L - H)+ and M(L - 2H) complexes, in which the protons are released from the coordinated OH group. A pM vs pH correlation showed that replacing an NH2 group with a OH group in tren or NN(2)O222 makes the resulting metal complex less stable. Electronic spectra showed that the Cu(II) complexes of both NNO(2)222 and NN(2)O222 adopted a square pyramidal geometry rather than a trigonal bipyramidal geometry. The X-ray crystal structure analysis of the zinc complex [Zn(OH)(mu-NNO(2)222 - H)Zn(NNO(2)222)]2+, as its [BF4]- salt, shows a dinuclear molecule containing two zinc ions, each coordinated in a distorted trigonal bipyramid. The coordination environment at one zinc atom is composed of the four donor groups of a mono-O-deprotonated ligand NNO(2)222 and a hydroxyl ion with the central nitrogen atom of the ligand and the hydroxyl ion in equatorial positions. The oxygen atom of the deprotonated alkoxo group bridges to the second zinc atom, which is coordinated by this atom and one undeprotonated ligand NNO(2)222.     

离子色谱-电感耦合等离子体质谱法测定植物性样品中的碘及其形态

建立了离子色谱-电感耦合等离子体质谱联用(IC-ICP/MS)测定植物性样品中碘及其形态的方法。采用碱提取法处理样品后,应用IC-ICP/MS检测植物样品中的碘离子和碘酸根;采用高温裂解法处理样品,使样品中各种形态的碘最终均转化为碘离子,然后应用IC-ICP/MS检测碘离子,从而实现总碘的测定。碘的方法检出限为0.010 mg/kg。碱提取法和高温裂解法处理样品的碘的加标回收率分别为89.6%～97.5%和95.2%～111.2%,结果令人满意。按照所建立的方法分别考察了紫菜、海带、圆白菜、茶叶、菠菜等常见植物性样品中碘的存在形式,结果表明,紫菜中的碘以有机碘为主,而海带、圆白菜、茶叶、菠菜中的碘则以无机碘为主。     

Gas chromatographic determination of pesticides in vegetable samples by sequential positive and negative chemical ionization and tandem mass spectrometric fragmentation using an ion trap analyser

A selective and sensitive chromatographic method is described for the determination of nine organochlorine and organophosphorus pesticides in vegetable samples by gas chromatography-mass spectrometry. The proposed method combines the use of positive and negative chemical ionisation and tandem mass spectrometric fragmentation, resulting in a significant increase in selectivity and allowing the simultaneous confirmation and quantification of trace levels of pesticides in complex vegetable matrices. Parameters relative to ionisation and fragmentation processes were optimised to obtain maximum sensitivity. Repeatability and reproducibility studies yielded relative standard deviations lower than 25% in all cases. Identification criteria, such as retention time and relative abundance of characteristic product ions, were also evaluated in order to guarantee the correct identification of the target compounds. The method was applied to real vegetable samples to demonstrate its use in routine analysis.     

Interaction of Mo(CO)6 and its derivative fragments with the Cu(001) surface: Influence on the decomposition process

A theoretical study on the adsorption and decomposition of molybdenum carbonyl on the copper (001) surface is reported. The adsorption structures and energies of Mo(CO)_n molecules (n = 1 … 6) are computed systematically using density functional theory with Van der Waals corrections. By analyzing the energies of the various conformations, the main factors that determine the stable adsorption geometry are identified. Insight into the thermodynamics of decomposition is gained by calculating the reaction energy for dissociation of Mo(CO)_n into Mo(CO)_n?1 and CO. In the gas phase, this reaction is highly endothermic for all n. On the Cu surface, however, removal of the first CO group (n = 6) becomes strongly exothermic. The subsequent dissociation steps (n < 6), are endothermic even on the surface, but the reaction energies are much reduced. Dissociation is found energetically more favorable than desorption in all cases. The results clearly show that molybdenum carbonyl decomposition is strongly facilitated by the presence of the Cu surface. © 2014 Wiley Periodicals, Inc.     

Optimized precursor ion selection for labile ions in a linear ion trap mass spectrometer and its impact on quantification using selected reaction monitoring

The fragmentation of fragile ions during the application of an isolation waveform for precursor ion selection and the resulting loss of isolated ion intensity is well‐known in ion trap mass spectrometry (ITMS). To obtain adequate ion intensity in the selected reaction monitoring (SRM) of fragile precursor ions, a wider ion isolation width is required. However, the increased isolation width significantly diminishes the selectivity of the channels chosen for SRM, which is a serious problem for samples with complex matrices. The sensitive and selective quantification of many lipid molecules, including ceramides from real biological samples, using a linear ion trap mass spectrometer is also hindered by the same problem because of the ease of water loss from protonated ceramide ions. In this study, a method for the reliable quantification of ceramides using SRM with near unity precursor ion isolation has been developed for ITMS by utilizing alternative precursor ions generated by in‐source dissociation. The selected precursor ions allow the isolation of ions with unit mass width and the selective analysis of ceramides using SRM with negligible loss of sensitivity. The quantification of C18:0‐, C24:0‐ and C24:1‐ceramides using the present method shows excellent linearity over the concentration ranges from 6 to 100, 25 to 1000 and 25 to 1000 nM, respectively. The limits of detection of C18:0‐, C24:0‐ and C24:1‐ceramides were 0.25, 0.25 and 5 fmol, respectively. The developed method was successfully applied to quantify ceramides in fetal bovine serum. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of amoxicillin in pharmaceuticals using sequential injection analysis and multivariate curve resolution

In this study, we report a method for quantifying amoxicillin in pharmaceuticals in the presence of interferents using sequential injection analysis (SIA) with a diode-array spectrophotometric detector and multivariate curve resolution with alternating least squares (MCR-ALS). With a suitable analytical sequence, we can use SIA to generate a pH gradient and, for each sample, obtain a data matrix. We used augmented matrices to resolve the system and obtain the spectra and concentration profiles of the components in the sample.We studied what are the effects of imposing trilinearity at the resolution stage, how to choose the species that will be used for quantification (acid, basic or the sum of the two), and which is the most suitable concentration of the reference standard. Once the optimum conditions were established, we performed the quantification in three amoxicillin-containing pharmaceuticals (flubiotic, augmentine, and clamoxyl). With this method, determination is quick, the reactants and instrumentation are inexpensive, and pretreatment of the sample is unnecessary.     

Rapid monitoring and sensitive determination of DDT and its metabolites in water sample using solid-phase extraction followed by ion mobility spectrometry

Dichlorodiphenyl trichloroethane (DDT) as an organochlorine compound has been globally used as a pesticide for controlling soil-dwelling insects and treating diseases such as malaria and typhus. The degradation products of DDT and its metabolites have also negative effects on the environment. The present study has investigated the determination of DDT and its metabolites in water sample using ion mobility spectrometry (IMS) as a rapid and sensitive detection technique. For this purpose, DDT and its metabolites were extracted using reverse phase solid-phase extraction (SPE) from water samples. The samples were then recovered by eluting with methanol and finally, quantified using the corona discharge IMS technique. Injection and oven temperatures and the effect of dopant were optimized as experimental parameters influencing both detection and determination efficiencies. Degradation of DDT in IMS drift tube was studied and reduced mobility values of DDT and its metabolites were calculated. The developed method was validated using water sample to obtain good results for the determination of DDT at low levels (1 ng ml^?1) while spiked recoveries were obtained to be between 95.0–96.7%. The proposed method based on IMS proved to be a simple, inexpensive, rapid and sensitive procedure for the fast monitoring and determination of DDT and its main metabolites in water sample.     

Thallium fractionation in polluted environmental samples using a modified BCR three-step sequential extraction procedure and its determination by electrothermal atomic absorption spectrometry

Determination of thallium in polluted environmental samples and their extracts obtained by a modified BCR three-step sequential extraction procedure was used to study thallium distribution and mobility in the monitored polluted area affected by acidification (Šobov, Central Slovakia). The results of fractionation applied to 5 soil certified reference materials and 14 environmental samples show that the vast majority of thallium occurred in the residual fraction. This means that highly toxic thallium is strongly entrapped in the parent rock materials remains immobile and its environmental toxicity is therefore reduced. The limit of detection for thallium in the studied fractions was lower than 0.050 mg kg⁻¹, the precision (RSD) of the ultratrace determination of thallium in the studied fractions was better than 17 % and the accuracy of the used method was verified by analyzing certified reference materials. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.