Thermospray Mass Spectrometry Research Articles

Anion-Catalyzed Dissolution of NO2 on Aqueous Microdroplets

Fifty-seven years after NO(x) (NO + NO(2)) were identified as essential components of photochemical smog, atmospheric chemical models fail to correctly predict *OH/HO(2)* concentrations under NO(x)-rich conditions. This deficiency is due, in part, to the uncertain rates and mechanism for the reactive dissolution of NO(2)(g) (2NO(2) + H(2)O = NO(3)(-) + H(+) + HONO) in fog and aerosol droplets. Thus, state-of-the-art models parametrize the uptake of NO(2) by atmospheric aerosol from data obtained on "deactivated tunnel wall residue". Here, we report experiments in which NO(3)(-) production on the surface of microdroplets exposed to NO(2)(g) for approximately 1 ms is monitored by online thermospray mass spectrometry. NO(2) does not dissolve in deionized water (NO(3)(-) signals below the detection limit) but readily produces NO(3)(-) on aqueous NaX (X = Cl, Br, I) microdroplets with NO(2) uptake coefficients gamma that vary nonmonotonically with electrolyte concentration and peak at gamma(max) approximately 10(-4) for [NaX] approximately 1 mM, which is >10(3) larger than that in neat water. Since I(-) is partially oxidized to I(2)(*-) in this process, anions seem to capture NO(2)(g) into X-NO(2)(*-) radical anions for further reaction at the air/water interface. By showing that gamma is strongly enhanced by electrolytes, these results resolve outstanding discrepancies between previous measurements in neat water versus NaCl-seeded clouds. They also provide a general mechanism for the heterogeneous conversion of NO(2)(g) to (NO(3)(-) + HONO) on the surface of aqueous media.

Reliability of ventilatory parameters during cycle ergometry in multicentre trials in COPD

We studied the distribution profiles and repeatability of key exercise performance parameters in the first large multicentre trials to include these measurements in chronic obstructive pulmonary disease (COPD). After a screening visit, 463 subjects with COPD (mean+/-SD forced expiratory volume in 1 s 43+/-13% predicted) completed two run-in visits before treatment randomisation. At the run-in visits, measurements were conducted at rest, at a standardised time near end-exercise (isotime) and at peak exercise during constant work rate (CWR) cycle tests at 75% of each individual's maximum work capacity. The intraclass correlation coefficient was used to evaluate the test-retest repeatability of measurements of endurance time (ET), inspiratory capacity (IC), ventilation and dyspnoea intensity (Borg scale) during exercise. IC, ventilation and dyspnoea ratings were normally distributed; ET showed rightward skew (median<mean, skewness of 10.9 (much greater than zero)) with 16% of the sample exceeding 1 SD of the mean. ET was highly repeatable across run-in visits: 7.9+/-4.8 and 8.4+/-5.1 min (R = 0.84). IC values at rest, isotime and peak exercise were all highly repeatable (R > or = 0.87). Ventilation was repeatable over the same time-points (R > or = 0.92), as was dyspnoea intensity at isotime (R = 0.79) and at peak exercise (R = 0.81). In conclusion, key perceptual and ventilatory parameters can be reliably measured during CWR cycle exercise in multicentre clinical trials in moderate to very severe COPD.

Wish to die in end-stage ALS

We investigated the metabolism of hexafluoropropene, a nephrotoxic fluoroalkene, in rat liver and kidney subcellular fractions and in rats in vivo. Incubation of hexafluoropropene (1 mM) with microsomes and cytosol in the presence of glutathione (GSH) yielded S-(1,2,3,3,3-pentafluoropropenyl)glutathione (PPFG) and S-(1,1,2,3,3,3-hexafluoropropyl)glutathione (HFPG) as identified by thermospray mass spectrometry and 1H-NMR. In liver microsomes, PFPG formation was predominant (240 nmol/min/mg protein) over HFPG (36 nmol/min/mg), whereas in cytosol, HFPG was the only hexafluoropropene metabolite (136 nmol/min/mg) detectable. In kidney microsomes, GSH-conjugate formation could not be detected; in kidney cytosol, HFPG was exclusively formed (46 nmol/min/mg). Hexafluoropropene inhalation (800 ppm for 1 hr) in rats fitted with a biliary cannula resulted in the biliary elimination of PFPG without detectable formation of HFPG; the exclusively formed urinary metabolite, identified by GC/MS, was N-acetyl-S-(1,1,2,3,3,3-hexafluoropropy)-L-cysteine. The results show that hexafluoropropene is metabolized to two different GSH-conjugates in rat liver and kidney. The data also suggest that hexafluoropropene metabolites formed in the liver and eliminated with bile are not translocated to the kidney and that intrarenal bioactivation by GSH-conjugation may be responsible for hexafluoropropene-induced nephrotoxicity.

23-Carboxy-24,25,26,27-tetranorvitamin D 3 (calcioic acid) and 24-carboxy-25,26,27-trinorvitamin D 3 (cholacalcioic acid): End products of 25-hydroxyvitamin D 3 metabolism in rat kidney through C-24 oxidation pathway

During the past two and half decades the elucidation of the metabolic pathways of 25OHD 3 and its active metabolite 1α,25(OH) 2D 3 progressed in parallel. In spite of many advances in this area of vitamin D research, the unequivocal identification of the end products of 25OHD 3 metabolism through C-24 oxidation pathway has not been achieved. It is now well established that both 25OHD 3 and 1α,25(OH) 2D 3 are metabolized through the same C-24 oxidation pathway initiated by the enzyme 24-hydroxylase (CYP24A1). Based on the information that the end product of 1α,25(OH) 2D 3 metabolism through C-24 oxidation pathway is 1α-OH-23- COOH-24,25,26,27-tetranor D 3 or calcitroic acid; the metabolism of 25OHD 3 into 23-COOH-24,25,26,27-tetranor D 3 has been assumed. Furthermore, a previous study indicated 24-COOH-25,26,27-trinor D 3 as a water soluble metabolite of 24 R,25(OH) 2D 3 produced in rat kidney homogenates. Therefore, 24-COOH-25,26,27-trinor D 3 was also assumed as another end product of 25OHD 3 metabolism through C-24 oxidation pathway. We embarked on our present study to provide unequivocal proof for these assumptions. We first studied the metabolism of 25OHD 3 at low substrate concentration (3 × 10 −10 M) using [1,2- 3H]25OHD 3 as the substrate in the perfused rat kidneys isolated from both normal and vitamin D 3 intoxicated rats. A highly polar water soluble metabolite, labeled as metabolite X was isolated from the kidney perfusate. The amount of metabolite X produced in the kidney of a vitamin D intoxicated rat was about seven times higher than that produced in the kidney of a normal rat. We then produced metabolite X in a quantity sufficient for its structure identification by perfusing kidneys isolated from vitamin D intoxicated rats with high substrate concentration of 25OHD 3 (5 × 10 −6 M). Using the techniques of electron impact and thermospray mass spectrometry, we established that the metabolite X contained both 23-COOH-24,25,26,27-tetranor D 3 and 24-COOH-25,26,27-trinor D 3 in a ratio of 4:1. The same metabolite X containing both acids in the same ratio of 4:1 was also produced when 24 R,25(OH) 2D 3 was used as the starting substrate. Previously, the trivial name of cholacalcioic acid was assigned to 24-COOH-25,26,27-trinorvitamin D 3. Using the same guidelines, we now assign the trivial name of calcioic acid to 23-COOH-24,25,26,27-tetranor D 3. In summary, for the first time our study provides unequivocal evidence to indicate that both calcioic and cholacalcioic acids as the end products of 25OHD 3 metabolism in rat kidney through C-24 oxidation pathway.

Unprecedented Matrix-Induced Reduction of Flavins Observed Under FAB and MALDI Conditions

Flavin-derived compounds such as riboflavin, riboflavin 5-phosphate (flavin mononucleotide, FMN) and flavin-adenine dinucleotide (FAD), under matrix-assisted laser desorption ionization (MALDI) and fast atom bombardment (FAB) conditions produce unprecedented reduced species that can be attributed to [M+2H]+. and [M+3H]+ in addition to the anticipated [M+H]+ ions. On the other hand, electrospray ionization (ESI) conditions generate only the expected [M+H]+ as the sole molecular-related ion. A protonation from the matrix accompanied by a concomitant electron transfer, rather than the transfer of hydrogen atom(s), [H. of CH groups], is proposed to explain the observed reduction process. The reduction site expands to N(1)=C(10a)-C(4a)=N(5), a 1,4-diaza-1,3-butadiene system, in the isoalloxazine ring, resembling the behavior of prosthetic groups of aerobic dehydrogenases. Interestingly, CID-MS / MS of most abundant molecular-related ions generated by the FAB and ESI modes, namely [M+2H]+. for FAB and [M+H]+ for ESI, produce the identical even-electron fragment ion of isoalloxazine moiety, indicating a radical loss vs. the evenelectron molecule loss from the individual precursor ions. The observed phenomena are compared with those previously reported for FABMS, thermospray mass spectrometry (TSPMS) and ESIMS. Keywords: Matrix-Induced Reduction, Flavins, thermospray, prosthetic groups, aerobic dehydrogenases

Simultaneous quantitative determination method for ceramide species from crude cellular extracts by high-performance liquid chromatography–thermospray mass spectrometry

I have developed a simple method which enabled simultaneous analysis of ceramides in the subcellular fractions from cultured cells by HPLC–thermospray mass spectrometry. The HPLC–thermospray mass spectra from ceramide standards were characterized by the high intensity of the MNa + and MH +–H 2O ions. As the other minor ions, MK +, MH + and m/ z 282 ions were detected. Although the preponderance of MNa + ions compared with the MH +–H 2O ions was detected in non-hydroxy fatty acid-ceramides, the preponderance of MH +–H 2O ions based on the elimination of the hydroxyl group introduced at the α-position of acyl-portion compared with the MNa + ions was detected in α-hydroxy fatty acid-ceramides. In calibrations for authentic ceramides using N-octanoylsphingosine as an internal standard, an approximately linear relationship existed between the ratios of peak-areas of each ceramide to that of the internal standard and the known amounts of each ceramide. The factor ( f) of each ceramide was calculated as follows; N-oleoyl- d-sphingosine ( f=0.45), N-palmitoyl- d-sphingosine ( f=0.40), N-stearoyl- d-sphingosine ( f=0.39), N-nervonoyl- d-sphingosine ( f=0.39) and N-lignoceroyl- d-sphingosine ( f=0.35). In subcellular fractions from A549 and HepG2 cells, although ceramide species content per mg protein was high in the nuclear envelope fractions, the 7000 g pellet fractions and the 100 000 g pellet fractions, a large portion of the ceramide species was concentrated in the nuclear envelope fraction. In addition, this method was applied to a mild alkaline hydrolyzate of total ceramides from pig stratum corneum, and MNa +/MH +–H 2O ions corresponding to several ω-hydroxyacyl-ceramides were detected.

Characterization of proanthocyanidins from grape seeds

Leucoselect™ (grape seed selected proanthocyanidins) was analyzed. HPLC thermospray mass spectrometry (TSP-MS) allowed the detection of monomeric flavan-3-ols and dimeric proanthocyanidins. Fractionation over Sephadex® LH-20 resin and analysis of the isolated fractions by gel permeation chromatography (GPC) and electrospray mass spectrometry (ESI-MS) led to the complete characterization of the proanthocyanidin constituents of Leucoselect™. The analysis revealed the presence of approximately 15% of (+)-catechin (1) and (−)-epicatechin (2), 80% of (−)-epicatechin 3- O-gallate (3), dimers, trimers, tetramers and their gallates and 5% of pentamers, hexamers, heptamers and their gallates.

Differences between marine and terrestrialPhoma species as determined by HPLC-DAD and HPLC-MS

Ethyl acetate extracts of 26 terrestrial and 16 marine derived Phoma spp. were analysed using RP-HPLC coupled with diode-array detection and thermospray mass spectrometry. For all samples, the retention times, UV and mass spectral data were determined. Twenty-two mass spectral data points from single fungal metabolites could be identified as being discriminative between the two groups of fungi and were analysed by regression analysis. The occurrence of these mass units allowed 84% of all of the extracts to be confirmed as being derived from either the terrestrial or the marine samples. This finding suggests that marine-derived Phoma spp. differ significantly from terrestrial Phoma spp. with respect to their secondary metabolite content. The number of detected secondary metabolites per strain, and the number of compounds per strain which were unique to the marine-derived Phoma spp. did not differ markedly from the findings with their terrestrial counterparts. Copyright © 2000 John Wiley & Sons, Ltd.

Detection of the principal synthetic route indicative impurity in Lamotrigine

An analytical method has been developed for the detection of trace amounts of the principal synthetic route indicative impurity in lamotrigine (3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine). A sample extract was preconcentrated by normal-phase high-performance liquid chromatography (HPLC) and analysed by subsequent on-line reversed-phase HPLC–thermospray mass spectrometry (TSP-MS). During the sample extraction and concentration step, carried out by semipreparative normal-phase chromatography, the preliminary separation of the impurity from the lamotrigine takes place. The organic solvent (dichloroethane–methanol, 90:10, v/v) is evaporated from the collected fraction and the material is redissolved in a smaller volume of the reversed-phase mobile phase. The collected fraction is then subjected to reversed-phase HPLC–TSP-MS. The influence of an ultrasonic extraction step has been examined. When the method was applied to lamotrigine tablets, a shake flask partitioning step using 1 mg/ml EDTA in water–dichloroethane was used instead of the ultrasonic extraction. Detection limit and recovery measurements showed that the route indicative impurity formed during the synthesis could be detected in the 50–100 ppb (w/w) range.

Concentrations and dynamics of free mono- and oligosaccharides in a shallow eutrophic lake measured by thermospray mass spectrometry

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 16:281-293 (1999) - doi:10.3354/ame016281 Concentrations and dynamics of free mono- and oligosaccharides in a shallow eutrophic lake measured by thermospray mass spectrometry Benedikt Meon*, Friedrich Jüttner Institute of Plant Biology/Limnology, University of Zürich, Limnological Station, Seestr. 187, CH-8802 Kilchberg, Switzerland *Present address: College of Marine Studies, University of Delaware, Lewes, Delaware 19958, USA. E-mail: bmeon@udel.edu ABSTRACT: Short-term, diel and annual variations in sugar concentrations (hexoses and oligosaccharides) were determined in a shallow eutrophic lake (Lake Au, Switzerland) by high performance liquid chromatography-thermospray mass spectrometry (HPLC-TSMS), a technique previously not used for the quantitative determination of mono- and oligosaccharides in aquatic environments. Concentrations of total hexoses and total disaccharides were extremely low in comparison to previous studies and showed little variations on an annual time scale with values <1 to 48 nM (mean: 13 nM) and <1 to 77 nM (mean: 9 nM), respectively. The low values can be attributed to the reliability of the mass spectrometric method that used labelled internal standards, which were added immediately after sampling, and the use of hollow-fibre filtration to remove delicate organisms without damage from the soluble fraction. The low concentrations also indicate the existence of high affinity sugar uptake systems in aquatic microbial communities. Trisaccharide and tetrasaccharide concentrations were below the detection limit of 2 nM on most sampling dates. The total carbon content of the mono- and oligosaccharides represented 0.003 to 0.3% of the dissolved organic carbon (DOC). We observed neither a trend in sugar concentration over the year, nor a dependence on phytoplankton density, but transient pulses of sugar concentrations occurred on an hourly time scale, suggesting a tight coupling between release and uptake of sugars. Average decrease rates of oligosaccharides (maltose, maltotriose, maltotetraose) that were added as substrates to in situ exposed 5 l microcosms ranged between 27 and 50 nmol l-1 h-1. Both the high decrease rates and the absence of cleavage products in the course of the incubations support the assumption that uptake of intact oligosaccharides by microheterotrophs was responsible for the decrease in concentrations. Furthermore, the immediate decrease of the added maltooligosaccharides demonstrate that these sugars are frequently used substrates in lakewater. This could not be confirmed for 3-O-b-galactopyranosyl-D-arabinose, for which a decrease in concentration was only observed after 29 h. These experiments indicate that the sugar composition of oligosaccharides and their type of linkage are important features influencing their bioavailability to microheterotrophs. KEY WORDS: Thermospray mass spectrometry · Dissolved free carbohydrates · DOC · Oligosaccharides · Sugar dynamics · Lakewater Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 16, No. 3. Publication date: February 24, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Rapid detection of dihydrocodeine by thermospray mass spectrometry

Rapid assay of dihydrocodeine (DHC) by thermospray mass spectrometry is explored. Liquid–liquid extractions of blood, urine and gastric contents were injected into a thermospray mass spectrometer, to which there was no column connected, and DHC was assayed by the flow injection method. The mass spectra of DHC under thermospray ionization and filament-on ionization modes consist of the MH + ion of m/ z 302 alone, which was clearly detected in the samples. Although DHC should be quantitated by gas chromatography–mass spectrometry, this method is applicable for rapid identification of DHC in biological materials.

Electrochemical thermospray mass spectrometry—anodic oxidation of N,N-dialkylanilines

Abstract The coupling of an electrochemical cell on-line with a thermospray mass spectrometer can be used for the identification of reaction products. The objective of this study was to demonstrate the performance of electrochemical thermospray mass spectrometry (ETMS). The anodic oxidation of N , N -dialkylanilines in 0.1 M NH 4 OAc was studied. Structural information on the products were obtained by measurements in D 2 O-based electrolyte solution. The first step was the oxidation of dialkylaniline to radical cations. Recombination of the radical cations formed benzidine as the chief product. In the main side reaction the radical cations were deprotonated at the C–H acid α -carbon atom to radicals. A part of these radicals was oxidised at the electrode to immonium ions. By follow up reactions, such as hydrolysis, dealkylation, oxidation and recombination with monomeric radical cations, dimers were formed. Repeating the side reaction, these dimers reacted to give trimers and higher oligomers. A scheme of the different reaction pathways is presented.

Electrochemical Thermospray Mass Spectrometry Instrumentation for Coupling Electrochemistry to Mass Spectrometry

Reaction products in electrochemical processes can be identified by coupling an electrochemical thin-layer flow cell to a thermospray mass spectrometer. The performance of this analytical method, electrochemical thermospray mass spectrometry, is demonstrated. This includes the characterization of the improved electrochemical thin-layer flow cell. This cell offers the possibility to combine cyclic voltammograms with mass spectrometry. This goal was achieved, too, by the construction of a new thermospray ion source and a special vacuum recipient.

Analysis of cannabinoids by liquid chromatography— Thermospray mass spectrometry and liquid chromatography— Tandem mass spectrometry

A rapid method based on liquid chromatography and thermospray mass spectrometry without any derivatization or pre-purification steps has been developed for the identification and quantification of cannabinoids in drugs from cannabis plants. The extracts were separated on a C18 reversed-phase column with an acidic acetonitrile-water gradient. Liquid chromatographymass spectrometry was performed with a thermospray interface and protonated molecular ions were obtained from the cannabinoids of interest. Liquid chromatography-tandem mass spectrometry experiments on the molecular ions gave additional structural information online. The sensitivity and selectivity of the method was sufficient to enable the detection of 100 pg of the cannabinoids.

Resolution and quantitative determination of coeluted pesticide mixtures in liquid chromatography–thermospray mass spectrometry by multivariate curve resolution

Resolution and quantitative determination of a mixture of coeluted pesticides (carbofuran, propoxur and pirimicarb) in liquid chromatography–thermospray mass spectrometry by multivariate curve resolution is shown. Carbofuran and pirimicarb both exhibit an ion with m/z 239 in their thermospray mass spectrum. For the first compound this ion is attributed to the ammonium adduct [M+NH4]+ ion, whereas the corresponding ion of pirimicarb is the protonated molecule, [M+H]+. A third carbamate, propoxur, was added because this compound partly coelutes with carbofuran under normal experimental conditions during multiresidue analysis of carbamates with C18 packed analytical columns. With this additional compound, the so-called suppression effects on the ion formation of these compounds in thermospray mass spectrometry and their quantitative resolution using chemometric methods were studied.

Anodic oxidation of aniline and N-alkylanilines in aqueous sulphuric acid studied by electrochemical thermospray mass spectrometry

Anodic oxidation of aniline and N-alkylanilines in aqueous sulphuric acid studied by electrochemical thermospray mass spectrometry

Anodic oxidation of aniline and N-alkylanilines in aqueous sulphuric acid studied by electrochemical thermospray mass spectrometry

Electrochemical thermospray mass spectrometry (ETMS) is a suitable method for the investigation of electrode processes. The mechanism of the anodic oxidation of N,N-dialkylanilines in neutral aqueous solution and of phenothiazine in organic electrolyte solution have already been clarified by ETMS. By modification of the experimental setup, it is now possible to examine acidic electrolytes. The anodic oxidation of anilin, leading to the conducting polymer polyaniline and the anodic oxidation of N-alkylanilines were chosen for testing the new method. Thermospray mass spectra for aniline and N-alkylanilines as well as electrochemically generated products are shown. The potential dependent formation of dimeric and trimeric products and their structures are presented. A mechanism for the oxidation process is proposed.

In vitro metabolism of GV150013X by using liver microsomes and liver tissue slices from different species.

The metabolism of GV150013X was studied in vitro using washed liver microsomes and liver tissue slices from different species. This work was carried out in order to compare the metabolite profiles resulting from incubation of GV150013X with human, rat, dog and rabbit liver microsomes and those from rat, rabbit and human liver tissue slices. This compound was found to be converted to at least 8 metabolites by rat and human liver microsomes. In rabbit liver microsomes, the three metabolites M4, M7 and M8, and in dog liver microsomes metabolite M1, were not detected. The main metabolites, M2, M5 and M6, were present in human, rat and rabbit liver tissue slices, while the three metabolites M3, M4 and M8 and metabolite M1 were not detected in rabbit and rat liver tissue slices, respectively. In rat liver tissue slices, the major metabolites plus five minor metabolites, one sulphate conjugate of a monohydroxylated, three trihydroxylated and one dihydroxylated were identified based on HPLC retention time and thermospray-mass spectrometry data. Quantitative species differences among rat, dog, rabbit and human were observed, while qualitative differences only between rabbit and other species were detected.

Identification of soyasaponins by liquid chromatography–thermospray mass spectrometry

Saponins are important bioactive molecules widespread in the plant kingdom. Soyasaponins, isolated from Glicine max (Leguminosae), have been shown to exhibit various biological activities, e.g., an inhibitory effect on lipid-oxidation and liver-lesion generation and an improving effect on hyper-cholesteremia. Mass spectral investigation of these metabolites requires soft ionization techniques such as desorption chemical ionization, fast atom bombardment and thermospray mass spectrometry. A high-performance liquid chromatographic method was developed for thermospray mass spectrometric analysis of saponins contained in soybean flour extracts. The analyses were performed using a ternary eluent (water–acetonitrile–methanol) in gradient conditions with post-column addition of aqueous ammonium acetate. Six saponin components could be separated and identified. The mass spectra obtained provided information concerning both molecular masses and aglycone composition.

A Rare Mass Spectrometric Neutral Loss of 48 u

Fast atom bombardment and thermospray mass spectrometry results are consistent with the 2-deoxyfluoromethine derivative of the nucleoside (cytidine) shown below and designated 2DFC. However, a mass loss of 48 u from [M+H]+ (m/z258) was observed forming an abundant fragment ion atm/z210. The loss seemed peculiar since a 48 u neutral is more often associated with H3CSH or H3SiOH, which are not possible neutrals to be eliminated from 2DFC. Accurate mass measurement ofm/z210 indicated the 48 u neutral lost had the molecular formula CH4O2. Constant neutral loss (48 u) linked scan experiments showed the fragmentation (depicted below) is concerted within the microsecond time frame of the mass spectrometer. Other structurally homologous nucleosides, such as cytidine, do not exhibit this prominent fragmentation. Computerized molecular modeling was used to propose why the marked elimination occurs with 2DFC. © 1997 by John Wiley & Sons, Ltd.