Sensitivity of positive ion mode electrospray ionization mass spectrometry (ESI MS) in the analysis of purine bases in ESI MS and on-line electrochemistry ESI MS (EC/ESI MS)

A cone-shaped MS inlet and on-line electrochemistry (EC) were used to enhance the ionization efficiency in electrospray ionization mass spectrometry (ESI MS) of purine bases. A pathway of positive ion mode ESI may involve oxidation of purine bases, guanine, adenine, xanthine and hypoxanthine, by 1e⁻, 1H⁺ processes. The electrospray process generates dimers of purine bases that are detected in ESI MS as protonated ions, except for xanthine, for which a protonated radical dimer is detected. Thus electrochemical oxidation of purine bases during ESI may generate reactive radicals that can subsequently dimerize. Dimer formation is facilitated in ESI MS when the carrier solution pH is high. The positive ion mode ESI MS ionization is consistent with the reactivity of the bases toward oxidation. Furthermore, the formation of the protonated ions, and Na⁺ and K⁺ adducts of the bases, expected in positive ion ESI MS, are observed. In addition, unusual H-bonding of purine bases guanine and xanthine is confirmed by ESI MS. Application of low EC voltage to the on-line EC cell in EC/ESI MS improves the sensitivity and correlates with the decrease of the intensity of the dimers, possibly as a result of their further oxidation.     

ATRP poly(acrylate) star formation: A comparative study between MALDI and ESI mass spectrometry

Optimised matrix-assisted laser desorption/ionisation (MALDI) and electrospray ionisation (ESI) mass spectrometry (MS) methodologies were systematically compared in terms of their relative abilities to identify distinct chemical species present in samples associated with a polymer mechanistic study. In order to perform the investigation, formation processes involved in atom transfer radical polymerisation (ATRP) mediated methyl acrylate (MA) star polymerisations were studied. In addition to the 4-armed ATRP initiator employed in the polymerisations, initiator side-products were found to generate oligomeric chains. At a relatively high monomer to polymer conversion, terminal Br loss was observed in these oligomers; this Br loss was hypothesised to occur via degradative transfer reactions involving the radicals (CH₃)₂?OH, ?H₃ and ?H₂COCH₃, which were derived from the acetone used as a solvent in the polymerisations, as well as hydrogen radicals donated by the ligand N,N′,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA). In performing these studies, ESI was found to identify a greater number of distinct chemical species in the samples under investigation when compared to the employed MALDI technique, suggesting that the utilisation of ESI must be strongly considered in polymer mechanistic investigations if the maximum number of end-group functionalities within a given polymer sample are to be identified.     

Analysis of solvent dyes in refined petroleum products by electrospray ionization mass spectrometry

Solvent dyes are used to color refined petroleum products to enable differentiation between gasoline, diesel, and jet fuels. Analysis for these dyes in the hydrocarbon product is difficult due to their very low concentrations in such a complex matrix. Flow injection analysis/electrospray ionization/mass spectrometry in both negative and positive mode was used to optimize ionization of ten typical solvent dyes. Samples of hydrocarbon product were analyzed under similar conditions. Positive electrospray ionization produced very complex spectra, which were not suitably specific for targeting only the dyes. Negative electrospray ionization produced simple spectra because aliphatic and aromatic moieties were not ionized. This enabled screening for a target dye in samples of hydrocarbon product from a spill.     

Thermal degradation of poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer: comparative study by SEC/NMR, SEC/MALDI-TOF-MS and SPME/GC-MS

By comparing size exclusion chromatography/matrix assisted laser desorption ionisation (SEC/MALDI) and SEC/NMR spectra from virgin poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer, we were able to understand the bimodal distribution observed in poloxamer 407. Propylene oxide, isomerised to allyl alcohol during polymerisation, eventually forms a Poly(ethylene oxide-propylene oxide) diblock copolymer when EO is added to the feed. The oxidative thermal degradation of poloxamer 407 at 80°C in air was studied. We found by MALDI that degradation starts after 21 days in the PPO block of the copolymer. This result was confirmed by solid phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS): The first volatile degradation product to appear is 1,2-propanediol,1-acetate,2-formate. The structure of this molecule suggests that a six-ring intramolecular decomposition reaction of the PPO chain occurs at the very beginning of the polymer breakdown. Thus, the secondary hydroperoxide formed on the PPO chain plays a major role on the thermoxidation of poloxamer materials.     

采用快速蒸发电离质谱技术对化妆品开展质量溯源

随着社会经济的不断进步和物质生活的丰富,化妆品的使用已经越来越普遍。在经济利益驱动下,市场上假冒伪劣化妆品的情况日益严重,但是现行质量溯源主要是通过信息溯源进行,所以建立一种高精度、快速便捷的化妆品质量溯源技术方法是十分必要的。本文采用快速蒸发电离质谱技术（REIMS）对正品化妆品及市售样品进行检测,采用Live ID软件,分别对正、负离子模式下的液状样品和乳状样品进行聚类分析,构建PCA-LDA模型,查找可疑的伪品。随后,应用正品化妆品样品构建判别模型,并对市售样品进行鉴定,确定伪造化妆品。使用Progenesis QI软件对真伪化妆品进行差异因子分析并鉴定,确定主要质量溯源靶标因子,为将来化妆品真伪快速检测技术标准化及特征靶标物种定量检测奠定基础。     

Investigation of DNA-protein cross-link formation between lysozyme and oxanine by mass spectrometry

Reactive nitrogen species are implicated in inflammatory diseases and cancers. Oxanine (Oxa) is a DNA lesion product originating from the guanine base through exposure to nitric oxide, nitrous acid, or N-nitrosoindoles. Oxanine was found to mediate formation of DNA-protein cross-links (DPCs) in the cell extract. We have previously characterized two DNA-protein cross-links from the reaction between Oxa and glutathione: namely, the thioester and the amide. In this study, lysozyme was used to study site-specific modification on protein by Oxa moieties in DNA. With the aid of nanoLC coupled with nanospray ionization tandem mass spectrometry, addition of Oxa was found at Lys13, Lys97, Lys116, Ser85, and Ser86 of lysozyme when it was treated with 2'-deoxyoxanosine (dOxo). Furthermore, incubation of lysozyme with Oxa-containing calf thymus DNA, produced by treating DNA with nitrous acid, led to lysozyme modification at Lys116, Ser85, and Ser86. Interestingly, none of the cysteine residues was modified by dOxo, in contrast with our previous findings that dOxo reacted with oxidized glutathione disulfide, forming the thioester. This might be due to the half-life of the dOxo-derived thioester being 2.2 days at the pH of incubation. Furthermore, the sites of modifications on lysozyme are in good agreement with the solvent accessibility of the residues. Since repair of Oxa-derived DPCs has not been extensively investigated, these results suggest that these stable DPCs might represent important forms of cellular damage caused by reactive nitrogen species involved in inflammationrelated diseases.     

(S)- and (R)-fluoxetine as native markers in mass spectrometry (MS) binding assays addressing the serotonin transporter

A recently established and validated LC-ESI-MS/MS method for quantification of fluoxetine was used to implement MS binding assays for the human serotonin transporter (hSERT)-the primary target in the treatment of depression and emotional disorders. As a label-free screening technique, MS binding assays offer the opportunity to perform kinetic, saturation and competition assays using both (S)- and (R)-fluoxetine as native markers. In kinetic experiments, an association rate constant (k(+1) of 0.92±0.17×10(6) M(-1) s(-1) and a dissociation rate constant (k(-1)) of 0.0032±0.0002 s(-1) for (S)-fluoxetine binding to hSERT were determined. Saturation experiments provided K(d) values of 4.4±0.4 nM and 5.2±0.9 nM for (S)- and (R)-fluoxetine, respectively; statistical analysis revealed that the two enantiomers are equipotent. In competitive experiments with (S)-fluoxetine as a marker, K(i) values were obtained for various known inhibitors with a broad range of affinities for hSERT that correlate well with literature data obtained from radioligand binding experiments with [(3)H]imipramine. Additional competitive experiments using (R)-fluoxetine as a marker led to K(i) values for SERT inhibitors that deviate only marginally from those determined using the (S)-enantiomer. No changes in the rank order of affinities occurred, indicating that there is no difference in the binding characteristics of the two enantiomers.     

Characterisation of end groups in poly(2-hydroxyethyl methacrylate) by means of electrospray ionisation-mass spectrometry/mass spectrometry (ESI-MS/MS)

Poly(2-hydroxyethyl methacrylate) (poly(HEMA)) has been characterised by means of electrospray ionisation-mass spectrometry/mass spectrometry (ESI-MS/MS), in order to evaluate this technique for the generation of end group information. Low energy collision-induced dissociation (CID) data from poly(HEMA) enabled information on both end groups of the polymer chain to be gleaned, in a similar fashion to that proposed previously for other methacrylate polymer systems. Exact-mass CID information was employed to aid the understanding of the dissociation mechanism of the polymer. Some additional fragmentation pathways, compared to other methacrylate polymer systems, are proposed. An example of how software can aid the interpretation of the MS/MS data is also shown.     

Application of ESI and MALDI‐TOF MS for triacylglycerols analysis in edible oils

Triacylglycerols (TAG) are the most important group of compounds present in vegetable oils. These biomolecules, determining the physical, chemical and nutritional properties of the oils, are considered to be good fingerprints for quality and authenticity control. Therefore, TAGs characterization is a very important task in edible oil field, which has been undertaken by different analytical methods. The analysis of vegetable oils is still dominated by classic determinations, which are however laborious and time‐consuming and cannot be used routinely. More recently, advances in MS instrumentations coupled with online separation techniques and data processing have contributed to great expansion of MS in oil study, allowing the development of innovative analytical approaches that exhibit higher sensitivity, accuracy and rapidity in vegetable oils investigations. In the present contribution, a review of the most relevant applications of novel mass spectrometric techniques, such as ESI and MALDI, both alone and hyphenated with HPLC, used for analysis of the complex TAGs mixture of edible oils is illustrated.     

Analysis of flame structure by molecular-beam mass spectrometry using electron-impact and synchrotron-photon ionization

Molecular-beam mass spectrometry (MBMS) has proven to be a powerful tool for the general analysis of flame structure, providing concentrations of radical and stable species for low-pressure flat flames since the work of Homann and Wagner in the 1960’s. In this paper, we will describe complementary measurements using electron-impact ionization with a high-mass-resolution quadrupole mass spectrometer and vacuum-ultraviolet photoionization in a time-of-flight mass spectrometer. Isomers are resolved that have not been separately detectable before in MBMS studies of flames, including C₃H₂, C₃H₄, C₄H₃, C₄H₄, C₄H₅, C₆H₆, and C₂H₄O. The qualitative and quantitative results of MBMS have led to advances in modeling and applying flame chemistry. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 58–63, November–December, 2006.     

Molar mass distributions of polymers from size exclusion chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry: Methods for comparison

Equations are presented for calculating molar mass averages and molar mass distributions from matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) data and from size exclusion chromatography (SEC) data. The utility of polydispersity is examined as an indicator of the expectation of MALDI‐TOF MS mass discrimination effects. Cumulative distributions are found to be rich in information for comparing the two techniques and are easily obtained from both SEC and MALDI‐TOF MS data. Analyses of a series of narrow molar mass distribution poly(methyl methacrylate) (PMMA) standards and one polydisperse sample have been performed with both methods. MALDI‐TOF MS did not detect dimer and trimer in the PMMA samples, and it often indicated lower amounts of high‐molar‐mass polymers than did SEC. The results showed that the distribution breadth, as evidenced by the standard deviation of the distribution (calculated from the polydispersity and number‐average molar mass), correlated well with the molar mass range observed in the MALDI‐TOF MS spectra, whereas the polydispersity alone did not. Ratioing the extremes in the molar mass concentrations measured with the SEC differential refractometer, which were necessary to adequately define molar mass distributions, showed that detector dynamic range values as high as approximately 370,000 were required for the polydisperse samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 627–639, 2005     

Matrix‐assisted laser desorption/ionization mass spectrometry of synthetic polymers. VI. Analysis of phenol–urea–formaldehyde cocondensates

Phenolic resoles can be regarded as copolymers of phenol and formaldehyde that are distributed in the chain length and the number of methylol groups per molecule. While other spectroscopic methods like FTIR and NMR only give average structures, MALDI–TOF mass spectrometry is able to resolve the oligomer distribution of phenolic resoles. Using 2,5‐dihydroxybenzoic acid or 2,4,6‐trihydroxyacetophenone as matrices, MALDI–TOF spectra are obtained where each oligomer peak can be assigned to a particular chemical structure. Thus, the degree of polymerization and the number of reactive methylol groups can be determined. For urea‐modified resoles, in addition to phenol–formaldehyde and urea–formaldehyde structures, for the first time, phenol–urea–formaldehyde cocondensate structures can be identified directly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2540–2548, 2003     

Characterization of bis‐(phenoxy)phosphazene polymers using radio frequency glow discharge mass spectrometry

A radio frequency glow discharge mass spectrometry (rf‐GDMS) source is evaluated for future applications in the “fingerprint” characterization of polyphosphazene membranes. The rf‐GDMS spectra of a series of bis(phenoxy)phosphazene polymers contain ions that originate from both the phosphazene backbone and the phenoxy moiety, resulting in signature ions of the polymer family. “Fingerprint” ions from the substituted R‐group on the phenoxy moiety of the different derivatives allows the individual polymers to be distinguished from one another. The ability of the rf‐GDMS source to characterize these materials directly in the solid state will be useful for the continued application of these polymers as separation membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 954–961, 2000     

Electrochemical studies on the binding of a carcinogenic anthraquinone dye, Purpurin (C.I. 58 205) with DNA

The interaction of the anthraquininoid dye, Purpurin (C.I. 58 205) with fish-sperm DNA was electrochemically investigated in 0.02 mol L⁻¹ pH 7.0 Britton–Robinson (B–R) buffer. After interaction with DNA, the irreversible oxidation peak of the dye decreased and underwent a positive shift of potential, suggesting intercalation between the dye and DNA, this being consistent with fluorescence quenching results. The binding constant (K) and binding site size (s) of the two species were 9.6 × 10⁶ L mol⁻¹ and 1.7 respectively, as determined using voltammetric titration, indicating that the dye was strongly bound to the DNA.     

UV laser desorption/ionisation mass spectrometry of the triruthenium clusters Ru3(CO)12−n(PPh3)n (n=1, 2 and 3)

The negative ion ultraviolet laser desorption mass spectra of Ru₃(CO)₁₂ and its triphenylphosphine derivatives Ru₃(CO)_12−n(PPh₃)_n (n=1–3) have been recorded using laser desorption/ionisation time-of-flight mass spectrometry (LDI-TOF-MS). The spectra contain peaks in the parent region together with peaks at higher masses due to extensive gas phase reactions. Substitution of one to three carbonyls by the bulky triphenylphosphine ligand has a number of interesting effects on the spectra, most notably, increasing the degree of coordinative unsaturation of the gas phase clusters in the molecular ion region and increasing the intensity of the subsequent high mass reaction products.     

Location of deep-sea shark (Centrophorus squamosus) glycerol ether lipid double bonds by nitric oxide chemical ionization mass spectrometry

Chemical ionization mass spectrometry with nitric oxide as the reactant gas has proved to be an efficient tool for locating the double bond in monoalkenylglycerols of type HO-CH₂-CHOH-CH₂-O-(CH₂)_n-1-CH=CH-(CH₂)_n-2-CH₃. These monoalkenylglycerols were extracted from the liver oil of the shark Centrophorus squamosus, which lives at depths ranging from 1000 m and deeper. The presence of characteristic acylium ions R₁CO⁺ and/or R₂CO⁺ allowed location of the double-bond position.