Sample Cone Voltage Research Articles

UPLC-QTOF-MS Method for Identification of Mango Leaf Tea Metabolites

Abstract Objectives The study aim was to identify bioactive compounds in mango leaf tea using a new method - UPLC/Q-TOF-MS. Mango leaf tea is a natural product being investigated to manage type 2 diabetes due to its phytochemical properties. Methods Mango tea was extracted using 80% methanol overnight. The extract was analyzed with ultra-high-performance liquid chromatography-quadrupole time-of-flight (UPLC-Q-TOF) MS system (Waters Corp., Milford, MA) and injected into an Acquity UPLC BEH C18 column (2.1 mm × 100 mm, 1.7 µm, Waters Corp.). The column was equilibrated with distilled water containing 0.1% formic acid (FA) and eluted by a linear gradient of acetonitrile (ACN) containing 0.1% FA at a flow rate of 0.35 mL/min for 10 min and 40 °C of column temperature. Results The eluents were analyzed by A Vion IMS Q-TOF MS (Waters Corp.) with positive and negative electrospray ionization (ESI). The scan range of TOF MS data was 50–1500 m/z, the scan time was 0.2 sec, and the capillary and sampling cone voltages were 3 kV and 40 V, respectively. The desolvation flow rate and temperature were 800 L/h and 400 °C, respectively, and the source temperature was 100 °C. Leucine-enkephalin ([M + H] = 556.2771 Da; [M-H] = 554.2615 Da), used as a lack mass, was infused at a flow rate of 0.35 μL/min and a frequency of 10 s to ensure mass measurement accuracy of the metabolites analyzed by the instrument. Mass spectral data were collected from m/z 50 to 1500 with a scan time of 0.2 s. Collision energy was ramped from 10 to 40 eV for the collection of MS/MS data. The metabolites Mangiferin, quercetin/isoquercetin and iriflophenone 3-beta-glucoside were identified using ChemSpider in negative mode while only mangiferin and quercetin were defined in positive mode with different intensites: Mangiferin (421.07), quercetin/isoquercetin (303.05) and irrflophenone 3- beta- glucoside (407.097) that confirmed their molar mass. Conclusions The UPLC/Q-TOF-MS technique is a practical and novel method for identifying the fragmentation pattern of metabolites in mango leaf tea by measuring accurate mass with excellent resolution and sensitivity. Funding Sources N/A.

Mass spectrometry in untargeted liquid chromatography/mass spectrometry metabolomics: Electrospray ionisation parameters and global coverage of the metabolome.

Liquid chromatography coupled to mass spectrometry (LC/MS) is a dominant analytical platform in metabolomics, because of the high sensitivity and resolution, thus enabling large-scale coverage of metabolomes. Correspondingly, electrospray ionisation (ESI) is the favoured ionisation method in untargeted LC/MS metabolomics given the ability to produce large numbers of ions. In the workflow of LC/ESI-MS metabolomics, maximising the ionisation efficiency over a wide mass range is inevitably an essential and determining step, subsequently defining the extent of coverage of the metabolome under investigation. Thus in this study, electronic factors related to the functioning of the ESI source, namely the capillary and sample cone voltages, were explored to investigate the influence on the data acquired in metabolomic investigations. Hydromethanolic samples from an untargeted study (sorghum plants responding dynamically to fungal infection) were analysed on a high-resolution/definition LC/ESI-MS system. Here the capillary and sample cone voltages of the ZSpray™ ESI source were varied between 1.5-3.0kV and 10.0-40.0V, respectively. The acquired data were processed with MarkerLynx™ software and analysed using central composite design response surface methodology and chemometric approaches (principal component analysis and orthogonal projection latent structures-discriminant analysis). The results evidently demonstrate that both capillary and sampling cone voltages not only significantly influence the recorded MS signals with regard to the number and abundance of features, but also the overall structure of the collected data. This consequently impacts on the information extracted from the data and thus affects coverage of the metabolome. The observations postulate in that, untargeted LC/MS metabolomics, 'what you see is what you ionise'. Although there is convergence of collected data under different ESI conditions, the nuances observed indicate that the exploration of different ion source settings could be the best trade-off in expanding and maximising the metabolome coverage in untargeted metabolomic experiments.

Rapid analysis of the skin irritant p-phenylenediamine (PPD) in henna products using atmospheric solids analysis probe mass spectrometry

Henna (Lawsonia inermis) is applied to stain keratin, present in hair, skin and fingernails, a red-orange or rust colour. Producers of temporary tattoos mix the aromatic amine compound, para-phenylenediamine (PPD) into natural henna to create ‘black henna’ that rapidly stains the skin black. However, PPD may cause severe delayed hypersensitivity reactions following skin contact. This study proposes a rapid direct-analysis method to detect and identify PPD using an atmospheric solids analysis probe (ASAP) coupled to a Q-ToF mass spectrometer (MS). Since laborious, multistep methods of analysis to determine PPD are undesirable, due to the instability of the compound in solution, a screening method involving no sample preparation steps was developed. Experiments were carried out to optimise the corona current, sample cone voltage, source temperature, and desolvation gas temperature to determine ideal ASAP-Q-ToF-MS analysing conditions. Eleven of the 109 henna samples, originating from various countries, tested positive for PPD when henna products were screened using ASAP-MS, without any form of sample preparation other than grinding. Ultra-performance liquid chromatography electrospray ionisation-mass spectrometry (UPLC-Q-ToF-MS) was subsequently used to confirm the results from ASAP and to determine the concentrations of PPD in henna products. The allergen was detected in the same eleven samples, with concentrations ranging from 0.05–4.21% (w/w). It can be concluded that the sensitivity of the ASAP-MS technique is sufficient (limit of detection=0.025% w/w) to allow screening of henna samples for the presence of PPD. This relatively new technique can be applied to commercial products without extraction, sample treatment or chromatographic separation.

Study of the hydrolytic properties of the trivalent Y-ion in chloride medium

Hydrolysis reactions of YCl3 aqueous solutions were studied by potentiometric titrations at 310K in the pH range ca.3–9 and total Y3+ ion concentration range 0.5–10.0mmol/dm3. The experimental data were evaluated with the aid of the Hyperquad2006 suite of programs, which indicated the formation of the following hydrolytic complexes (logconc. overall stability constants βp,q defined as βp,q=Mp(OH)q[H]q/[M]p), Y(OH)2+ (−7.71(2)); Y(OH)2+ (−16.42(2)); Y(OH)3 (−26.01(3)); Y2(OH)24+ (−14.23(4)); Y3(OH)52+ (−34.20(4)); Y4(OH)62+ (−37.10(5)). The hydrolysis of the Y3+ ion was also monitored by electrospray ionization ion-trap mass spectrometry (ESI-MS) in the pH range 2.63–7.10. The influence of the sample cone voltage on the product distribution was significant, indicating the contribution of ion source fragmentation reactions. The optimal cone voltage was set to 70V for cationic and 100V for anionic spectra. The cationic and anionic ESI mass spectra of the Y3+ solutions produced strong evidence for the presence of a variety of monomeric and polymeric hydrolytic complexes. The Cl− ion appeared to be a strong competitor to the OH− ion for the oxo-yttrium core. The hydrolytic precipitation reactions with NaOH or urea as precipitating agents were studied. The obtained precipitates were characterized by the potentiometric technique, elemental analysis, thermal analysis (TG-DSC), infrared spectroscopy, X-ray diffractions and the SEM technique. Hydrothermal synthesis of the precipitate in an autoclave at T=420K and P=10bar with NaOH as the precipitating agent produced a crystalline precipitate in the form of hexagonal needles (P63/m space group). At atmospheric pressure only an amorphous precipitate was produced with both precipitating agents. The concentration solubility product K∗so of Y(OH)3 was evaluated from the potentiometric titrations curves and logK∗so=−22.85(4). The synthesized precipitate with NaOH as a precipitating agent had a composition of Y(OH)3·2H2O, while the amorphous precipitate obtained with urea had a composition of Y2(OH)2(CO3)2·3H2O.

Rapid identification of polymer additives by atmospheric solid analysis probe with quadrupole time-of-flight mass spectrometry.

A method using an atmospheric solid analysis probe (ASAP) combined with quadrupole time-of-flight mass spectrometry (QTOFMS) assisted by a pre-built MS library was found to be efficient in fast and direct analysis of additives for polymers. By this method, sample pretreatment could be eliminated from the additives identification process. Some crucial parameters, such as desolvation gas temperature, corona current, sample cone voltage and collision energy, should be optimized. A MS library of 100 polymer additives, including phenols (Irganox 1010, Irganox 1076), hydroxyl phenyl benzotriazole derivatives (Tinuvin 326, Tinuvin 327, Tinuvin 328), hindered amines (Tinuvin 944, Tinuvin 770) and plasticizers, was built based on the optimized conditions. To verify the application of the MS library, the ASAP-QTOFMS method was applied to identify complex additives, a simulated polypropylene (PP) sample and a real polymethylmethacrylate (PMMA) sample purchased from a local market. By searching the exact mass, and comparing the MS and MS/MS spectra of samples with standards in the MS library, complex additives such as Irganox GX 2921, as well as additives in PP and PMMA samples, could be identified quickly and easily. The determination of mass accuracy increased the confidence of peak identification as well. Moreover, the results also provided information of the characterization for PP and PMMA polymers. A rapid identification method has been developed for polymer additives by ASAP-QTOFMS. A MS library of 100 polymer additives was built by this method. Using ASAP-QTOFMS assisted by the pre-built MS library, polymer additives can be quickly identified. This method was found to be a promising tool in the rapid analysis of additives in polymers and polymer matrices.

Atmospheric pressure solid analysis probe coupled to quadrupole-time of flight mass spectrometry as a tool for screening and semi-quantitative approach of polycyclic aromatic hydrocarbons, nitro-polycyclic aromatic hydrocarbons and oxo-polycyclic aromatic hydrocarbons in complex matrices

A new screening and semi-quantitative approach has been developed for direct analysis of polycyclic aromatic hydrocarbons (PAHs) and their nitro and oxo derivatives in environmental and biological matrices using atmospheric pressure solid analysis probe (ASAP) quadrupole-time of flight mass spectrometry (Q-TOF-MS). The instrumental parameters were optimized for the analysis of all these compounds, without previous sample treatment, in soil, motor oil, atmospheric particles (ashes) and biological samples such as urine and saliva of smokers and non-smokers. Ion source parameters in the MS were found to be the key parameters, with little variation within PAHs families. The optimized corona current was 4µA, sample cone voltage 80V for PAHs, nitro-PAHs and oxo-PAHs, while the desolvation temperatures varied from 300°C to 500°C. The analytical method performance was checked using a certified reference material. Two deuterated compounds were used as internal standards for semi-quantitative purposes together with the pure individual standard for each compound and the corresponding calibration plot. The compounds nitro PAH 9-nitroanthracene and oxo-PAH 1,4-naphthalenedione, were found in saliva and urine in a range below 1µg/g while the range of PAHs in these samples was below 2µg/g. Environmental samples provided higher concentration of all pollutants than urine and saliva.

An LC–MS screening method with library identification for the detection of steroidsin dietary supplements

For many years anabolic-androgenic steroids (AAS) are by far the most frequently detected pharmacological substances in doping control. In order to improve their performances, professional sportsmen are often tempted to take dietary supplements. However, due to the frequent and widespread occurrence of contaminated supplements, the use of such products is not without risk for the athletes involved. In order to minimize the chances of an unattended positive doping test or serious health problems, fast and reliable screening methods for the detection of anabolic steroids in dietary supplements are needed. A general screening procedure requires the fast and unambiguous detection of a large range of steroids. Gas chromatography-mass spectrometry (GC-MS) has been used intensively in the detection of doping substances for the past 40 years. Over time, many laboratories have delivered spectra to be included in standard reference databases, one of which is maintained by the National Institute of Standards and Technology (NIST) (Gaithersburg, MD, USA). In recent years, however, liquid chromatography coupled to mass spectrometry (LC-MS) has gained popularity. Unfortunately, existing GC-MS libraries are not applicable to LC-MS analysis. In the present study, a new mass spectral library of 88 steroids was developed, along with a fast UPLC-MS method. For the construction of this mass spectral library, three different mass spectra were measured for each steroid, with a sample cone voltage of 30, 60 and 100 V, respectively. This method was then successfully tested on contaminated dietary supplements which had previously been tested by means of a targeted LC-MS/MS method. Overall, the library search was shown to identify the same compounds as the MRM method.

Aluminum speciation of coagulants with low concentration: Analysis by electrospray ionization mass spectrometry

Aluminum speciation of coagulants with low concentration was investigated in detail by electrospray ionization mass spectrometry (ESI-MS). In particular, comparison with 27Al nuclear magnetic resonance ( 27Al NMR) and Ferron colorimetric method for aluminum speciation of coagulants was discussed. The results indicated that various hydrolyzed aluminum species (monomeric, dimeric, trimeric and tetrameric aluminum species), which could not be identified by other methods, appeared in ESI-MS spectra. Thus, ESI-MS method was much better for hydrolyzed aluminum species in low concentration. In this paper, sample cone voltage was an important operating parameter during ESI-MS detection, and optimum voltage was 70 V. Too low (40 V) or high (150 V) sample cone voltage was not suitable for detecting all aluminum species. This study also evaluated the effects of coagulant concentration, aging, pH value and organic matter on aluminum species distribution. The results indicated that the distribution of hydrolyzed aluminum species at low concentration was largely dependent on the solution pH. At higher pH conditions, aging (8–12 h) may influence aluminum hydrolysis. Additionally, after adding salicylic acid into coagulant solutions, speciation and stability for both Al 13 species and aluminum–salicylate complexes varied significantly at different pH values.

Stoichiometry of the Peripheral Stalk Subunits E and G of Yeast V1-ATPase Determined by Mass Spectrometry

The stoichiometry of yeast V(1)-ATPase peripheral stalk subunits E and G was determined by two independent approaches using mass spectrometry (MS). First, the subunit ratio was inferred from measuring the molecular mass of the intact V(1)-ATPase complex and each of the individual protein components, using native electrospray ionization-MS. The major observed intact complex had a mass of 593,600 Da, with minor components displaying masses of 553,550 and 428,300 Da, respectively. Second, defined amounts of V(1)-ATPase purified from yeast grown on (14)N-containing medium were titrated with defined amounts of (15)N-labeled E and G subunits as internal standards. Following protease digestion of subunit bands, (14)N- and (15)N-containing peptide pairs were used for quantification of subunit stoichiometry using matrix-assisted laser desorption/ionization-time of flight MS. Results from both approaches are in excellent agreement and reveal that the subunit composition of yeast V(1)-ATPase is A(3)B(3)DE(3)FG(3)H.

Sensitive profiling of chemically diverse bioactive lipids

Here, we present an improved method for sensitive profiling of lipids in a single high-performance liquid chromatography-electrospray ionization-quadrupole time of flight mass spectrometry experiment. The approach consists of i) sensitive isocratic elution, which takes advantage of C18 column material that is resistant to increased pH values induced by piperidine, ii) chemometric alignment of mass spectra followed by differential analysis of ion intensities, and iii) semiquantitative analysis of extracted ion chromatograms of interest. A key advantage of this method is its wide applicability to extracts that harbor lipids of considerable chemical complexity. The method allows qualitative and semiquantitative analysis of fatty acyls, glycerophospholipids (such as glycerophosphatidylinositols, glycerophosphatidylserines, and glycerophosphatidylcholines in brain extracts), phosphatidylinositol mannosides, acylated glycerophospholipids, sphingolipids (including ceramides and gangliosides in brain extracts), and, for the first time with ESI, prenols and mycolic acids (MAs). MAs are targets in antimycobacterial therapy, and they play an important immunomodulatory role during host-pathogen interactions. We compared high-resolution mass spectra of MAs derived from Mycobacterium bovis Bacille Camette-Guérin during entry into nonreplicative conditions induced by oxygen deprivation (hypoxic dormancy). Although the overall composition is not drastically altered, there are pronounced differences in individual MAs. alpha-MAs accumulate during entry into dormancy, whereas a subpopulation of keto-MAs is almost entirely eliminated. This effect is reversed upon resuscitation of dormant mycobacteria. These results provide detailed chemical information with relevance to drug development and immunobiology of mycobacteria.

Neisseria gonorrhoeae Type IV Pili Undergo Multisite, Hierarchical Modifications with Phosphoethanolamine and Phosphocholine Requiring an Enzyme Structurally Related to Lipopolysaccharide Phosphoethanolamine Transferases

The zwitterionic phospho-forms phosphoethanolamine and phosphocholine are recognized as influential and important substituents of pathogen cell surfaces. PilE, the major pilin subunit protein of the type IV pilus (Tfp) colonization factor of Neisseria gonorrhoeae undergoes unique, post-translational modifications with these moieties. These phospho-form modifications have been shown to be O-linked alternately to a specific, conserved serine residue of PilE. However, the enzymes and precursors involved in their addition are unknown, and the full spectrum of PilE post-translational modifications has yet to be defined. Here, an intact protein-based mass spectrometric approach was integrated with bioinformatics and reverse genetics to address these matters. Specifically we show that a protein limited in its distribution to pathogenic Neisseria species and structurally related to enzymes implicated in phosphoethanolamine modification of lipopolysaccharide is necessary for PilE covalent modification with phosphoethanolamine and phosphocholine. These findings strongly suggest that protein phospho-form modification is mechanistically similar to processes underlying analogous modifications of prokaryotic saccharolipid glycans. We also show that PilE undergoes multisite and hierarchical phospho-form modifications and that the stoichiometries of site occupancy can be influenced by PilE primary structure and the abundance of the pilin-like protein PilV. Together, these findings have important implications for the structure and antigenicity of PilE.

A Proteome Reference Map and Proteomic Analysis of Bifidobacterium longum NCC2705

A comprehensive proteomic study was carried out to identify and characterize proteins expressed by Bifidobacterium longum NCC2705. A total of 708 spots representing 369 protein entries were identified by MALDI-TOF-MS and/or ESI-MS/MS. Isoelectric point values estimated by gel electrophoresis matched closely with their predicted ones, although some discrepancies exist suggesting that post-translational protein modifications might be common in B. longum. The identified proteins represent 21.4% of the predicted 1727 ORFs in the genome and correspond to 30% of the predicted proteome. Moreover 95 hypothetical proteins were experimentally identified. This is the first compilation of a proteomic reference map for the important probiotic organism B. longum NCC2705. The study aimed to define a number of cellular pathways related to important physiological processes at the proteomic level. Proteomic comparison of glucose- and fructose-grown cells revealed that fructose and glucose are catabolized via the same degradation pathway. Interestingly the sugar-binding protein specific to fructose (BL0033) and Frk showed higher levels of expression in cells grown on fructose than on glucose as determined by semiquantitative RT-PCR. BL0033 time course and concentration experiments showed that the induction time and fructose concentration correlates to increased expression of BL0033. At the same time, an ABC (ATP-binding cassette) transporter ATP-binding protein (BL0034) was slightly up-regulated in cells grown on fructose compared with glucose. All of the above results suggest that the uptake of fructose into the cell may be conducted by a specific transport system in which BL0033 might play an important role.

Mass Spectrometric Analysis of the Ubiquinol-binding Site in Cytochrome bd from Escherichia coli

Cytochrome bd is a heterodimeric terminal ubiquinol oxidase in the aerobic respiratory chain of Escherichia coli. For understanding the unique catalytic mechanism of the quinol oxidation, mass spectrometry was used to identify amino acid residue(s) that can be labeled with a reduced form of 2-azido-3-methoxy-5-methyl-6-geranyl-1,4-benzoquinone or 2-methoxy-3-azido-5-methyl-6-geranyl-1,4-benzoquinone. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry demonstrated that the photo inactivation of ubiquinol-1 oxidase activity was accompanied by the labeling of subunit I with both azidoquinols. The cross-linked domain was identified by reverse-phase high performance liquid chromatography of subunit I peptides produced by in-gel double digestion with lysyl endopeptidase and endoproteinase Asp-N. Electrospray ionization quadrupole time-of-flight mass spectrometry determined the amino acid sequence of the peptide (m/z 1047.5) to be Glu(278)-Lys(283), where a photoproduct of azido-Q(2) was linked to the carboxylic side chain of I-Glu(280). This study demonstrated directly that the N-terminal region of periplasmic loop VI/VII (Q-loop) is a part of the quinol oxidation site and indicates that the 2- and 3-methoxy groups of the quinone ring are in the close vicinity of I-Glu(280).

Identification of the hydrolysis products of AlCl3.6H2O by electrospray ionization mass spectrometry.

The hydrolysis reactions of AlCl3 in 0.1 M aqueous solutions at pH 3.27-4.20 were monitored by electrospray ionization time-of-flight mass spectrometry (ESI-ToF MS) as a function of time. The cationic and anionic ESI mass spectra of aluminum(III) solutions gave strong evidence of the presence of a variety of monomeric and polymeric complexes. Competition between the OH- and Cl- ligands within the same aluminum core was observed. The influence of the sample cone voltage on the product distribution was also explored. The optimum sample cone voltage for the cationic spectra was 70 V. For the anionic spectra no optimum sample cone voltage was found and the appearance of the anionic spectra was strongly dependent on the sample cone voltage within the whole range explored.

The effect of glycerol on signal supression during electrospray ionization analysis of proteins

The effect of salts, detergents and chaotropic agents on mass spectrometric analysis are relatively well understood, mainly due to their actions decreasing the performance of ESI interface in mass spectrometric analysis. However, there are few studies in the literature characterizing the effect of protein stabilization by glycerol, followed in some circumstances by the suppression of protein signal when ESI interface is used. The aim of the present research was to investigate in details the mass spectrometric behavior of some proteins in presence of high levels of glycerol during ESI–MS analysis. Thus, horse heart myoglobin and chicken ovalbumin were used as standard proteins. It was demonstrated that the presence of 1% (v/v) glycerol suppressed the signal of these proteins during the ESI–MS analysis, even when the sample nozzle potential was scanned from 28 to 80 V. However, when the glycerol concentration was decreased to 0.5% (v/v) and the sample cone voltage adjusted to 50 V, a perfect envelope of peaks was observed, allowing the spectrum deconvolution and the molecular mass determination with mass accuracy lower than 0.01% in each situation. A molecular explanation for this suppressive effect and for the analytical overcoming of this difficult is proposed.

Mass spectrometric analysis of chemical warfare agents and their degradation products in soil and synthetic samples.

A packed capillary liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method was developed for the identification of chemical warfare agents, their degradation products and related compounds in synthetic tabun samples and in soil samples collected from a former mustard storage site. A number of organophosphorus and organosulfur compounds that had not been previously characterized were identified, based on acquired high-resolution ESI-MS data. At lower sampling cone voltages, the ESI mass spectra were dominated by protonated, sodiated and protonated acetonitrile adducts and/or their dimers that could be used to confirm the molecular mass of each compound. Structural information was obtained by inducing product ion formation in the ESI interface at higher sampling cone voltages. Representative ESI-MS mass spectra for previously uncharacterized compounds were incorporated into a database as part of an on-going effort in chemical warfare agent detection and identification. The same samples were also analyzed by capillary column gas chromatography (GC)-MS in order to compare an established method with LC-ESI-MS for chemical warfare agent identification. Analysis times and full-scanning sensitivities were similar for both methods, with differences being associated with sample matrix, ease of ionization and compound volatility. GC-MS would be preferred for organic extracts and must be used for the determination of mustard and relatively non-polar organosulfur degradation products, including 1,4- thioxane and 1,4-dithiane, as these compounds do not ionize during ESI-MS. Diols, formed following hydrolysis of mustard and longer-chain sulfur vesicants, may be analyzed using both methods with LC-ESI-MS providing improved chromatographic peak shape. Aqueous samples and extracts would, typically, be analyzed by LC-ESI-MS, since these analyses may be conducted directly without the need for additional sample handling and/or derivatization associated with GC-MS determinations. Organophosphorus compounds, including chemical warfare agents, related compounds and lower volatility hydrolysis products may all be determined during a single LC-ESI- MS analysis. Derivatization of chemical warfare agent hydrolysis products and other compounds with hydroxyl substitution would be required prior to GC-MS analysis, giving LC-ESI-MS a definite advantage over GC-MS for the analysis of samples containing chemical warfare agents and/or their hydrolysis products.

Packed capillary liquid chromatography–electrospray mass spectrometry of snow contaminated with sarin

Packed capillary liquid chromatography–electrospray mass spectrometry (LC–ESI-MS) was used for the analysis of a snow sample that was accidentally contaminated with an organophosphorus chemical warfare agent during the destruction of a chemical munition. Sarin, its hydrolysis products and a number of related compounds were identified on the basis of acquired LC–ESI-MS data. Full mass spectra were acquired for 14 compounds, with all exhibiting MH +, [MH+ACN] + ions and/or protonated dimers that could be used to confirm molecular mass. Sampling cone voltages from 20 to 70 V were utilized with the higher sampling voltages enhancing formation of structurally important product ions in the ESI interface. All data were acquired with a time-of-flight mass spectrometer with a resolution of 5000 (50% valley definition), a resolution that aided in the assignment of elemental composition of the observed ions. The application of LC–ESI-MS to snow analysis appears to be an attractive alternative to the GC–MS methods, since both chemical warfare agents and their hydrolysis products may be analysed directly, eliminating the need for additional sample handling and derivatization steps.

Molecular weight distributions of heavy aromatic petroleum fractions by Ag+ electrospray ionization mass spectrometry.

The ability of electrospray ionization mass spectrometry (ESI MS) to analyze heavy aromatic petroleum fractions using silver nitrate as a reagent compound to form characteristic adduct ions has been examined. The complexation of aromatic compounds containing long alkyl substituents with the silver ion leads to the formation of abundant adduct ions such as [M + Ag]+ and [2M + Ag]+. The concentration of the [2M + Ag]+ ions can be reduced by increasing the sampling cone voltage. Molecular ions and other adduct ions may also be formed depending on the structure of the aromatic molecule. Results obtained from the analysis of representative heavy petroleum fractions and vacuum residues by the Ag+ ESI MS method and conventional ionization methods were in good agreement. The current method extends the applicability of electrospray ionization to the analysis of neutral hydrocarbons in heavy aromatic petroleum fractions. It is simple and compatible with widely available LC/MS instrumentation. The extreme complexity of the Ag

Determination and characterization of diuretics in human urine by liquid chromatography coupled to pneumatically assisted electrospray ionization mass spectrometry

The aim of this work was to develop a method for the characterization and determination of diuretics in human urine samples by liquid chromatography (LC) coupled to pneumatically assisted electrospray ionization (ES) mass spectrometry (MS). The diuretics studied were substances forbidden by the IOC such as trichlormethiazide, furosemide, canrenoic acid, benzthiazide, bendroflumethiazide, bumetanide, etacrynic acid and spironolactone. For this purpose, the operational parameters of electrospray, such as counter electrode voltage, capillary voltage, sample cone voltage and source temperature, were optimized in order to obtain the best signal stability and the highest sensitivity for the greatest number of diuretic agents. The optimized separation method was successfully coupled with the MS system to analyze the above-mentioned diuretics extracted from spiked urine samples by a liquid extraction and clean-up procedure at basic pH, using ethyl acetate as solvent and the salting-out effect (NaCl). The mass spectra obtained provide adequate information for identification purposes. Positive urine samples obtained from athletes were also analyzed. The presence of these substances in human urine was confirmed by this method, making LC/ES-MS an analytical tool to be considered in the area of antidoping control.

Investigating the electrospray mass spectra of inorganic and organic antimony compounds

Positive- and negative ion electrospray mass spectra of commonly encountered organic antimony compounds, i.e., trimethylantimony dichloride (TMSbCl2) and trimethylantimony dihydroxide [TMSb(OH)2], and inorganic antimony compounds, i.e., potassium hexahydroxyantimonate [Sb(V)] and potassium antimonyl tartrate [Sb(III)] have been obtained using electrospray time-of-flight mass spectrometry (ES-TOF-MS). By operating the ES-TOF-MS instrument at high sample cone voltage (100 V), fragmentation information of TMSbCl2 and TMSb(OH)2 was obtained. Positive ion electrospray mass spectra have been found to be more useful for the identification of organic antimony compounds, TMSbCl2 and TMSb(OH)2, whereas negative ion electrospray mass spectra are more suitable for the identification of inorganic antimony compounds, Sb(V) and Sb(III). Based on the ES-MS results, a solution chemistry of TMSbCl2 and TMSb(OH)2 was proposed. Peaks at m/z 183 and 185 corresponding to [(CH3)3SbOH]+ can be considered as a characteristic fingerprint for the identification of trimethylantimony species (TMSb) in an aqueous solution when using a positive ion ES-MS technique. The characteristic fingerprint was applied for the identification of TMSbCl2, following its elution from a size-exclusion chromatography (SEC) column.