Positive Ion Electrospray Ionization Mass Research Articles

Identification and characterization of impurities in an insecticide, commercial chlorantraniliprole using liquid chromatography-tandem mass spectrometry.

Ensuring the global safety and effectiveness of agrochemicals has become imperative. An in-depth understanding of impurity profiles of products is crucial, especially for high-demand agrochemicals, where impurities may be more toxic and persistent than original agrochemicals. This study focuses on the detection and identification of impurities in a commercial chlorantraniliprole (CAP), an anthranilic diamide class broad-spectrum insecticide. Commercial CAP was collected from an agrochemical supplier in India and was analyzed using a high-performance liquid chromatography-photodiode array (HPLC-PDA) (Agilent 1260; wavelength, 220 nm) with a Zorbax RP SB-C18 (250 × 4.6mm, 5μm) column and liquid chromatography-mass spectrometry (LC-MS) (Agilent 6545 quadrupole time of flight (Q-TOF)) techniques to identify the impurities. The impurities were isolated by preparative HPLC using a Zorbax-DB C18 (250 × 9.4mm, 5μm) column. liquid chromatography- tandem mass spectrometry (LC-MS/MS) experiments (Q-TOF) were performed on CAP and its impurities to obtain their structural data. HPLC-PDA analysis of CAP showed four major impurities (IM-1 to IM-4) ranging from 0.76% to 4.1%. The positive ion electrospray ionization (ESI) mass spectra of CAP and its impurities showed dominant [M + H]+ ions in addition to [M + Na]+ , [M + K]+ , and [2M + Na]+ ions. High-resolution mass spectrometry (HRMS) data provided the elemental composition of the compounds, and isotopic distribution patterns revealed the number of Cl and/or Br atoms present in them. The structures of impurities were proposed based on the LC-MS/MS) data and further confirmed by nuclear magnetic resonance (NMR) data on isolated impurities/synthesis. The quality and impurities of CAP, a popular insecticide, must be assessed and described for its efficacy and safety. In this study, four impurities of CAP were detected using HPLC and successfully characterized using LC-HRMS, LC-MS/MS, and NMR data. The method is useful for verifying the purity of CAP as well as helping in the identification of its possible impurities.

Development of ultrahigh-performance liquid chromatography/mass spectrometry and ultrahigh-performance supercritical fluid chromatography/mass spectrometry assays to determine the concentration of Bitrex™ and sodium saccharin in homemade facemask fit testing solutions.

RationaleFast and easily transferable chromatography/mass spectrometry assays were required to detect and quantify the amount of Bitrex™ and sodium saccharin in homemade facemask fit testing solutions.MethodsBitrex™ solutions were analysed using reversed‐phase ultrahigh‐performance liquid chromatography coupled with positive ion electrospray ionisation mass spectrometry (UHPLC/ESI‐MS). Separation was achieved using a mobile phase gradient with an Acquity BEH C18‐packed column. Sodium saccharin solutions were analysed using ultrahigh‐performance supercritical fluid chromatography coupled with negative ion electrospray ionisation (UHPSFC/ESI‐MS). Separation was achieved using isocratic elution with an Acquity UPC2 Torus Diol packed column and a methanol (25 mM ammonium acetate) co‐solvent.ResultsThe calibration curves obtained using the ratio of the active compound to an internal standard generated linear regression values (R2) >0.99. Samples analysed prior to and after an autoclave sterilisation process and bottling gave repeatable measurements within 10% of the expected concentration.ConclusionsThe two assays afford a fast robust and quantitative analytical method for the detection of the active components used to test the efficacy of the homemade facemask testing solutions.

A validated HPTLC method for the simultaneous quantifications of three phenolic acids and three withanolides from Withania somnifera plants and its herbal products

A simple, rapid and selective high-performance thin-layer chromatographic (HPTLC) method has been developed and validated for simultaneous determination of three withanolides (withaferin A, withanone and withanolide A) and three phenolic acids (caffeic acid, ferulic acid and benzoic acid) from different parts (root, stem and leaf) of Withania somnifera and its two commercially available polyherbal formulations. The extraction efficiency of withanolides and phenolic acids were tested using two solvents, chloroform and methanol, respectively. HPTLC separation was performed on silica coated aluminium plates Si 60F254; using toluene, ethyl acetate and acetic acid (60:40:4). The samples were quantitated at 231 nm. The purity and identity of peaks of all the six analytes were confirmed by matching Rf values and UV-spectrum with authentic standards. The identity of three withanolides was further confirmed by positive ion electrospray ionization mass spectrometry (ESI-MS/MS) analyses. The developed method was validated for sensitivity, linearity, reproducibility, accuracy, the limit of detection (LOD) and limit of quantification (LOQ) following the guidelines of the International Conference on Harmonization (ICH). The method was found to be linear (r > 0.99) in the range of 50–2000 ng/band for benzoic acid and 50–1000 ng/band for the other five studied metabolites. This simple and accurate HPTLC method provided enhanced resolution of studied analytes as compared to other phytoconstituents present in W. somnifera extracts. It has also been successfully applied in the analysis and quantification of two polyherbal formulations containing W. somnifera plant parts.

Quantitative analysis of a multicomponent system for liquid chromatography–mass spectrometry determination of diosgenin, dioscin and protodioscin in plant extracts of Tribulus terrestris

An approach for the simultaneous determination of dioscin, protodioscin, and diosgenin in plant extracts by the liquid chromatography–mass spectrometry method with detection limits from 5 to 20 ng mL–1 is developed. Reversed-phase chromatography with the C18 sorbent followed by positive ion electrospray ionization and tandem mass spectrometric detection is used to analyze plant extracts. The external calibration and the quantitative analysis of multicomponent system are used to calculate the content based on peak areas in the chromatograms of the extracted ions. The difference between the results is shown to be less than 10%. The proposed approach is tested in the analysis of ethanolic and aqueous methanolic extracts of the aerial parts of Tribulus terrestris.

RuII, IrIIIand OsIImesoionic carbene complexes: efficient catalysts for transfer hydrogenation of selected functionalities

Pyridine-appended triazolylidene donors have been recently used as ligands in various homogeneous catalytic processes. We present here a new pyrimidine substituted triazolium salt which was prepared and used in the coordination to RuII and OsII. The new triazolium salt and the obtained complexes were characterized by multinuclear NMR spectroscopy. The molecular composition of the mentioned compounds was confirmed by positive ion electrospray ionization (ESI+) mass spectra. The new pyrimidyl containing complexes, as well as the related pyridyl-triazolylidene containing complexes, were applied in transfer hydrogenation reactions of carbonyls, alkenes, imines and nitroarenes. The pyrimidyl containing complexes reveal an over-all better activity in comparison to their pyridine bearing analogues. The studies of electronic effects of the ligands, as well as mechanistic insights for the reduction of nitrobenzene with three selected precatalysts are presented.

Novel formation of [2M-H](+) species in positive electrospray mass spectra of indoles.

When subjected to positive ion electrospray ionisation (ESI+) mass spectrometry (MS), indoles with a 3-alkyl substituent show a propensity to form novel [2M-H](+) 'covalently bound dimers'. This process, which appears to be initiated in the nebuliser of the instrument, is mechanistically interesting, analytically useful and potentially significant in organic synthesis. A selection of 2- and 3-substituted indoles have been synthesised and analysed by ESI-MS. The formation of the 'homo' and 'hetero' dimers of these compounds has been investigated using ESI+ mode. The mechanism of formation of the observed 'dimeric' species has been probed by synthesising authentic samples of the dimeric compounds. 'Dimeric' species corresponding to [2M-H](+) have been observed for all 3-substituted indoles studied, but not for indoles substituted in just the 2-position. By infusing equimolar mixtures of labelled and unlabelled indoles through the instrument, the expected approximately statistical mixture of homo- and heterodimeric species has been observed. Further experiments have established that this novel dimerisation occurs in the droplets formed in the nebuliser of the instrument. It has been shown that 3-substituted indoles form [2M-H](+) dimers in high abundance in the spray obtained from the nebiliser of an ESI+ instrument. The mechanism for the dimerisation does not involve the known 2M dimeric species that is readily formed in the solution-phase chemistry of indoles.

Monitoring Haloperidol Exposure in Body Fluids and Hair of Children by Liquid Chromatography–High-Resolution Mass Spectrometry

Haloperidol, 4-[4-(4-chlorophenyl)-4-hydroxy-1-piperidinyl]-1-(4-fluorophenyl)-1-butanone (HP), one of the most widely used antipsychotics in the treatment of schizophrenia, mania, and other psychiatric disorders, is frequently encountered in cases of unintentional pediatric intoxication because the ingestion of a small amount can cause significant toxic effects in children. For monitoring HP in suspected ingestions, a liquid chromatography-high-resolution mass spectrometry method has been developed and validated in urine, blood, and hair samples. The analyte was extracted from 1 mL blood or urine by liquid/liquid extraction and from 5 mg of hair by micropulverized extraction; gradient elution on an Atlantis T3 column was realized using HP-d4 as an internal standard. Positive ion electrospray ionization and high-resolution mass spectrometry determination were performed in an Orbitrap mass spectrometer. The method exhibited a r > 0.999 in the studied ranges (0.1-50 ng/mL in urine and blood and 0.1-50 ng/mg in hair) and a limit of quantification of 0.1 ng/mL for urine and blood and 0.1 ng/mg for hair; intra-assay and interassay relative SDs were always more than 18%. The method was applied to determine haloperidol in 3 children who were admitted to emergency departments. HP concentrations ranged from 2 to 21 ng/mL in urine, from not detected to 4.9 ng/mL in blood, and from 0.37 to 0.73 ng/mg in hair samples. The utilization of high-resolution/high-accuracy mass spectrometry in full scan mode allowed the identification of HP metabolites in urine and blood, thus unequivocally documenting the exposure to the drug. HP metabolites were structurally characterized by high-resolution multiple mass spectrometry. For the first time, a HP metabolite was detected in hair.

The relationship between electrospray ionization behavior and cytotoxic activity of [MI(P)4]+‐type complexes (M = Cu, Ag and Au; P = tertiary phosphine)

To try to find a correlation between the antiproliferative activity of a series of [M(I)(P)4](+) complexes (M = Cu, Ag and Au; P = tertiary phosphine) and their stability at micromolar concentration under mass spectrometric conditions. [M(I)(P)4](+) complexes were investigated by positive ion electrospray ionization mass spectrometry with multiple collisional experiments using an ion trap mass spectrometer. The displacement of P from native [M(I)(P)4](+), previously described for the copper derivative, is common for the triad complexes leading to the formation of [M(P)3](+) and [M(P)2](+) adducts. Further dissociation of [M(P)2](+) depends on the nature of the metal (Cu ~ Ag > Au). More labile [Cu(P)2](+) and [Ag(P)2](+) are more cytotoxic against HCT-15 human colon carcinoma cells compared to less labile [Au(P)2](+) species. The dissociation of P ligand(s) from the [M(I)(P)4](+) complexes is the driving force for the triggering of the antiproliferative activity. The more favored is the displacement of P from the [M(P)2](+) active form, the more favored is in turn the possibility for the metal to interact with biological substrates related to cancer proliferation.

Solution species of Fe(iii), Ga(iii), In(iii) or Ln(iii) and suberodihydroxamic acid from electrospray ionization mass spectrometry

Positive ion electrospray ionization mass spectrometry (ESI-MS) was used to characterize complexes formed in aqueous solution between Fe(III), Ga(III), In(III), Ce(III), Eu(III) or Yb(III), and the linear dihydroxamic acid suberodihydroxamic acid (HONHC(O)(CH2)nC(O)NHOH), n = 6; L6H4) at pH 2.5, and at metal (M) to ligand (L) ratios of 1 : 1 or 1 : 2. In the Ga(III)–L6H4 system, complexes with five different types of M : L stoichiometries were identified, with the major signals assigned to [Ga(L6H2)·CH3OH]+ (M : L, 1 : 1), [Ga(L6H2)(L6H3)] adducts (H+, Na+, K+) (M : L, 1 : 2), [Ga2(L6H2)2(μ-OCH3)]+ (M : L, 2 : 2), [Ga2(L6H2)3] adducts (H+, Na+, K+) (M : L, 2 : 3), or [Ga3(L6H2)4]+ (M : L, 3 : 4). Where M = Ce(III), Eu(III) or Yb(III), signals for [M(L6H2)(L6H3)] (H+ adduct) were dominant, signals for [M3(L6H2)4]+ were weak, and signals for [M2(L6H2)2(μ-OCH3)]+ were either weak (Ce(III)) or absent (Eu(III), Yb(III)), which reflected that the higher coordination number demands of lanthanide ions were not satisfied by the latter two stoichiometry types. An improved understanding of the solution speciation between different types of metal ions and hydroxamic acids is important in the context of the roles played by these ligands in bioremediation/biogeochemistry and biomedicine/imaging.

Mass Spectrometry of the Lithium Adducts of Diacylglycerols Containing Hydroxy FA in Castor Oil and Two Normal FA

AbstractCastor oil can be used in industry. The molecular species of triacylglycerols containing hydroxy fatty acids (FA) in castor oil have been identified. We report here the identification of twelve diacylglycerols (DAG) containing hydroxy FA in castor oil using positive ion electrospray ionization mass spectrometry of the lithium adducts. They were RR (diricinolein, R is ricinoleate), RL, RS, R‐diOH18:0, R‐diOH18:1, R‐diOH18:2, R‐triOH18:0, R‐triOH18:1, R‐triOH18:2, diOH18:0‐diOH18:1, diOH18:1‐diOH18:1 and diOH18:1‐diOH18:2. The MS2 fragment ions, [M + Li − FA]+ and [FA + Li]+, from the lithium adducts of DAG containing hydroxy FA (one or two hydroxy FA), were used for the identification. The additional fragment ions from the neutral losses of FA lithium salts [M + Li − FALi]+ were used for the identification of eleven DAG containing two normal FA in a soybean oil bioconversion product. The MS2 fragment ions from the neutral losses of FA lithium salts [M + Li − FALi]+ were not detected from the DAG containing hydroxy FA. The DAG containing FA with more hydroxyl groups than the other FA on the same DAG molecule tended to have a prominent fragment ion [FA + Li]+ and an undetectable fragment ion [M + Li − FA]+ while the FA was the more hydroxylated FA. Also the less hydroxylated FA of a DAG tended to have a prominent fragment ion [M + Li − FA]+ and an undetectable fragment ion [FA + Li]+ while the FA was the less hydroxylated FA.

Mass spectra of halogenostyrylbenzoxazoles

Several series of styrylbenzoxazoles of general formula XC6H3(NCO)CHCHC6H4Y [X=F, Cl or Br; Y=H, F, Cl, Br, CH3 or CH3O] have been investigated by positive ion electrospray and electron ionization mass spectrometry. These compounds, many of which are biologically active or have pharmaceutical potential, show in their electrospray spectra strong peaks for MH+ ions, which undergo relatively little fragmentation. The electron ionization spectra are extremely clean, being dominated by the loss of an atom or radical, Y, from the ortho position of the pendant ring, by a rearrangement that may be interpreted as a proximity effect. The resultant [M−Y]+ ions are exceptionally stable and rarely undergo further fragmentation. The analytical value of this proximity effect, which is analogous to intramolecular aromatic substitution, in revealing the presence of a substituent in the pendant ring and determining its position, is emphasized. Elimination of a species (including H or F) derived from an ortho substituent in the pendant ring occurs even when apparently more favourable alternative fragmentation is possible by direct cleavage of the CX bond (X=Cl or Br) in the benzoxazole ring.

Separation and identification of smokeless gunpowder additives by capillary electrochromatography

This paper details a method for the separation and identification of fourteen organic compounds commonly found as constituents in commercial smokeless powders using a hexyl acrylate-based porous monolith. Capillary electrochromatography (CEC) coupled to UV and time of flight-mass spectrometry (TOF-MS) methods were both explored. The CEC–UV method provides an effective and efficient method for the detection of all components in the additive package of the powder. The TOF-MS procedure provides better sensitivity and selectivity allowing an additional confirmation of the presence of the subset of those compounds, which are detectable via positive and/or negative ion electrospray ionization mass spectrometry. Both methods were used for the analysis of smokeless powder components in a mixed standard as well as in the determination of the composition of the additive package of individual powders.

Development and validation of liquid chromatography–mass spectrometric method for simultaneous determination of moxifloxacin and ketorolac in rat plasma: application to pharmacokinetic study

A highly sensitive, selective and rapid liquid chromatography-electrospray ionization mass spectrometry (LC-MS) method has been developed and validated for simultaneous determination of moxifloxacin (MFX) and ketorolac (KTC) in rat plasma. Gemifloxacin (GFX) was used as an internal standard (IS). A simple protein precipitation method was used for the extraction of analytes from rat plasma. Effective chromatographic separation of MFX, KTC and GFX was achieved on a Kromasil C(18) column (100 × 4.6 mm, 5 µm) using a mobile phase consisting of acetonitrile-10 mm ammonium acetate (pH 2.5)-0.1% formic acid (50:25:25) in an isocratic elution, followed by detection with positive ion electrospray ionization mass spectrometry using target ions of [M + H](+) at m/z 402 for MFX, m/z 256 for KTC and m/z 390 for GFX in selective ion recording mode. The method was validated over the calibration range of 5-100 ng/mL for MFX and 10-6000 ng/mL for KTC. The method demonstrated good performances in terms of intra- and inter-day precision (0.97-5.33%) and accuracy (93.91-101.58%) for both MFX and KTC, including lower and upper limits of quantification. The recoveries from spiked control samples were >75% for MFX and >79% for KTC. The matrix effect was found to be negligible and the stability data were within acceptable limits. Further, the method was also successfully applied to a single-dose pharmacokinetic study in rats. This method can be extended to measure plasma concentrations of both drugs in human to understand drug interaction and adverse effects.

Rapid and specific detection of urea nitrate and ammonium nitrate by electrospray ionization time‐of‐flight mass spectrometry using infusion with crown ethers

Urea nitrate (UN) and ammonium nitrate (AN) are fertilizer-based explosives that are commonly used in improvised munitions and can have highly destructive effects. Because they are in the form of salts, their relatively low volatility makes them difficult to detect at trace levels. In addition, these salts readily undergo metathetic reactions in water to form urea, ammonium and nitrate, which are ubiquitous in the environment. Thus, selective methods are needed for their detection. In this study, a procedure was developed to detect UN and AN in non-aqueous environments by positive ion electrospray ionization mass spectrometry through the addition of 18-crown-6. The method is sensitive, with detection limits under 2 μM, and selective. The procedure is capable of differentiating urea from uronium ions (protonated urea) and a mixture of urea and AN did not interfere with the UN signal. The procedure is quite versatile and the addition of crown ethers to the sample matrix does not interfere with the detection of high explosives in the negative ionization mode. Experimental results are presented on the utilization of the method in the detection of UN and AN on various surfaces. Semi-quantitative studies showed that AN and UN can be detected at trace levels following finger transfer and a series of studies were performed to demonstrate the effect of various interferences. The results show the method to be a quick and robust procedure for trace detection.

Development and validation of an enantioselective liquid-chromatography/tandem mass spectrometry method for the separation and quantification of eslicarbazepine acetate, eslicarbazepine, R-licarbazepine and oxcarbazepine in human plasma

The purpose of this study was develop and validate a sensitive and specific enantioselective liquid–chromatography/tandem mass spectrometry (LC–MS/MS) method, for the simultaneous quantification of eslicarbazepine acetate (ESL), eslicarbazepine (S-Lic), oxcarbazepine (OXC) and R-licarbazepine (R-Lic) in human plasma. Analytes were extracted from human plasma using solid phase extraction and the chromatographic separation was achieved using a mobile phase of 80% n-hexane and 20% ethanol/isopropyl alcohol (66.7/33.3, v/v). A Daicel CHIRALCEL ® OD-H column (5 μm, 50 mm × 4.6 mm) was used with a flow rate of 0.8 mL/min, and a run time of 8 min. ESL, S-Lic, R-Lic, OXC and the internal standard, 10,11-dihydrocarbamazepine, were quantified by positive ion electrospray ionization mass spectrometry. The method was fully validated, demonstrating acceptable accuracy, precision, linearity, and specificity in accordance with FDA regulations for the validation of bioanalytical methods. Linearity was proven over the range of 50.0–1000.0 ng/mL for ESL and OXC and over the range of 50.0–25,000.0 ng/mL for S-Lic and R-Lic. The intra- and inter-day coefficient of variation in plasma was less than 9.7% for ESL, 6.0% for OXC, 7.7% for S-Lic and less than 12.6% for R-Lic. The accuracy was between 98.7% and 107.2% for all the compounds quantified. The lower limit of quantification (LLOQ) was 50.0 ng/mL for ESL, S-Lic, OXC and R-Lic in human plasma. The short-term stability in plasma, freeze–thaw stability in plasma, frozen long-term stability in plasma, autosampler stability and stock solution stability all met acceptance criteria. The human plasma samples, collected from 8 volunteers, showed that this method can be used for therapeutic monitoring of ESL and its metabolites in humans treated with ESL.

Complexes formed in solution between vanadium(IV)/(V) and the cyclic dihydroxamic acid putrebactin or linear suberodihydroxamic acid.

An aerobic solution prepared from V(IV) and the cyclic dihydroxamic acid putrebactin (pbH2) in 1:1 H2O/CH3OH at pH = 2 turned from blue to orange and gave a signal in the positive ion electrospray ionization mass spectrometry (ESI-MS) at m/zobs 437.0 attributed to the monooxoV(V) species [VVO(pb)]+ ([C16H26N4O7V]+, m/zcalc 437.3). A solution prepared as above gave a signal in the 51V NMR spectrum at δV = −443.3 ppm (VOCl3, δV = 0 ppm) and was electron paramagnetic resonance silent, consistent with the presence of [VVO(pb)]+. The formation of [VVO(pb)]+ was invariant of [V(IV)]:[pbH2] and of pH values over pH = 2–7. In contrast, an aerobic solution prepared from V(IV) and the linear dihydroxamic acid suberodihydroxamic acid (sbhaH4) in 1:1 H2O/CH3OH at pH values of 2, 5, or 7 gave multiple signals in the positive and negative ion ESI-MS, which were assigned to monomeric or dimeric V(V)– or V(IV)–sbhaH4 complexes or mixed-valence V(V)/(IV)–sbhaH4 complexes. The complexity of the V-sbhaH4 system has been attributed to dimerization (2[VVO(sbhaH2)]+ ↔ [(VVO)2(sbhaH2)2]2+), deprotonation ([VVO(sbhaH2)]+ – H+ ↔ [VVO(sbhaH)]0), and oxidation ([VIVO(sbhaH2)]0 –e– ↔ [VVO(sbhaH2)]+) phenomena and could be described as the sum of two pH-dependent vectors, the first comprising the deprotonation of hydroxamate (low pH) to hydroximate (high pH) and the second comprising the oxidation of V(IV) (low pH) to V(V) (high pH). Macrocyclic pbH2 was preorganized to form [VVO(pb)]+, which would provide an entropy-based increase in its thermodynamic stability compared to V(V)–sbhaH4 complexes. The half-wave potentials from solutions of [V(IV)]:[pbH2] (1:1) or [V(IV)]:[sbhaH4] (1:2) at pH = 2 were E1/2 −335 or −352 mV, respectively, which differed from the expected trend (E1/2 [VO(pb)]+/0 < VV/IV–sbhaH4). The complex solution speciation of the V(V)/(IV)–sbhaH4 system prevented the determination of half-wave potentials for single species. The characterization of [VVO(pb)]+ expands the small family of documented V–siderophore complexes relevant to understanding V transport and assimilation in the biosphere.

Mass spectral analysis of N‐oxides of Chemical Weapons Convention related aminoethanols under electrospray ionization conditions

N,N'-Dialkylaminoethanols are the hydrolyzed products or precursors of chemical warfare agents such as V-agents and nitrogen mustards, and they are prone to undergo oxidation in environmental matrices or during decontamination processes. Consequently, screening of the oxidized products of aminoethanols in aqueous samples is an important task in the verification of chemical weapons convention-related chemicals. Here we report the successful characterization of the N-oxides of N,N'-dialkylaminoethanols, alkyl diethanolamines, and triethanolamine using positive ion electrospray ionization mass spectrometry. The collision-induced dissociation (CID) spectra of the [M+H](+) and [M+Na](+) ions show diagnostic product ions that enable the unambiguous identification of the studied N-oxides, including those of isomeric compounds. The proposed fragmentation pathways are supported by high-resolution mass spectrometry data and product/precursor ion spectra. The CID spectra of [M+H](+) ions included [MH-CH(4)O(2)](+) as the key product ion, in addition to a distinctive alkene loss that allowed us to recognize the alkyl group attached to the nitrogen. The [M+Na](+) ions show characteristic product ions due to the loss of groups (R) attached to nitrogen either as a radical (R) or as a molecule [R+H or (R-H)] after hydrogen migration.

Fragmentation patterns of novel dithiocarbamate derivatives with pharmaceutical activity under electrospray ionization tandem mass spectrometry conditions

The fragmentation patterns of a novel series of dithiocarbamate derivatives with pharmaceutical activity were investigated by positive ion electrospray ionization mass spectrometry in conjunction with tandem mass spectrometry (ESI-MS(n)). In the gas phase, the dithiocarbamate protonated molecules containing the piperazinium moiety undergo losses of bromide to form the piperazinium cation by ionization, followed by subsequent losses of methyl bromide, ring opening and rearrangement of piperazinium. Furthermore, the dithiocarbamate derivatives and their intermediates both undergo cleavage of the C-S bond to produce two common fragment ions. The different fragmentation observed for these compounds facilitated their identification and could be valuable in the further study of their metabolic pathways as prodrugs.

Characterization of oligomers from methylglyoxal under dark conditions: a pathway to produce secondary organic aerosol through cloud processing during nighttime

Abstract. Aqueous-phase oligomer formation from methylglyoxal, a major atmospheric photooxidation product, has been investigated in a simulated cloud matrix under dark conditions. The aim of this study was to explore an additional pathway producing secondary organic aerosol (SOA) through cloud processes without participation of photochemistry during nighttime. Indeed, atmospheric models still underestimate SOA formation, as field measurements have revealed more SOA than predicted. Soluble oligomers (n = 1–8) formed in the course of acid-catalyzed aldol condensation and acid-catalyzed hydration followed by acetal formation have been detected and characterized by positive and negative ion electrospray ionization mass spectrometry. Aldol condensation proved to be a favorable mechanism under simulated cloud conditions, while hydration/acetal formation was found to strongly depend on the pH of the system and only occurred at a pH&lt;3.5. No evidence was found for formation of organosulfates. The aldol oligomer series starts with a β-hydroxy ketone via aldol condensation, where oligomers are formed by multiple additions of C3H4O2 units (72 Da) to the parent β-hydroxy ketone. Ion trap mass spectrometry experiments were performed to structurally characterize the major oligomer species. A mechanistic pathway for the growth of oligomers under cloud conditions and in the absence of UV-light and OH radicals, which could substantially enhance in-cloud SOA yields, is proposed here for the first time.

Electrospray Ionization Tandem Mass Spectrometry of Phosphonate Peptides

Phosphonate peptides were synthesized and investigated by positive ion electrospray ionization mass spectrometry in conjunction with tandem mass spectrometry. It was found that, for the sodiated adduct, there were two rearrangement reactions. In path A, there was C-C covalent bond cleavage with consecutive migration of a hydrogen atom to lose the amino alcohol molecule. In path B, two consecutive covalent cleavages of the C-N and P-O bonds occurred.