Electrospray ionization ion-trap multistage mass spectrometric study of sodium cationized aldobiuronic and pseudoaldobiuronic acid derivatives

Fragmentation mechanisms of electrospray ionization (ESI) mass spectrometry of aldobiuronic and pseudoaldobiuronic acid derivatives were elucidated by multistage mass spectrometric (MS(n), n = 2-5) measurements of selected ions. Characteristic under the conditions of ESI-MS analysis is the production of alkali metal (Na and K) cationized adducts. The probability the of locations of Na cations in per-O-methylated compounds was proved by quantum chemical calculations, using the Jaguar program. The most probably position of alkali metal attachment is the carboxy group of the methoxycarbonyl C-5 group of the uronic acid unit. Characteristic cleavages vary according the kind of O-derivatization. In most cases they take place on the acidic part of the dimer and at the interglycosidic oxygen atom. As a result, the criteria for the differentiation of aldobiouronic and pseudoaldobiouronic acids derivatives were elucidated.     

Monitoring of yeast fermentation by ion mobility spectrometry measurement and data visualisation with Self-Organizing Maps

Ion mobility spectrometry (IMS) measurement combined with unsupervised neurocomputing is considered as a new potential method for on-line monitoring of fermentation and other processes producing volatile compounds that involve micro-organisms. This was demonstrated in a model system in which a strain of brewer’s yeast (Saccharomyces cerevisiae) was cultivated in a bench-top fermenter. Five phases of yeast growth could be detected from measurements of the exhaust gases from the fermenter, as indicated by the changes in ion mobility spectra analysed by computational methods.The data were first processed using the Self-Organizing Map (SOM) algorithm, the results showing that the phases of fermentation can be detected and identified. The cultivations were also shown by Sammon’s mapping to be comparable to a certain level of accuracy. Contaminated cultivation could be detected by its distinctive ion mobility spectrometry profile.     

Determination of manganese in brain samples by slurry sampling graphite furnace atomic absorption spectrometry

A simple procedure for the determination of manganese in different sections of human brain samples by graphite furnace atomic absorption spectrometry has been developed. Brain sections included cerebellum, hypothalamus, frontal cortex, vermix and encephalic trunk. Two sample preparation procedures were evaluated, namely, slurry sampling and microwave-assisted acid digestion. Brain slurries (2% w/v) could be prepared in distilled, de-ionized water, with good stability for up to 30 min. Brain samples were also digested in a domestic microwave oven using 5 ml of concentrated HNO₃. A mixed palladium+magnesium nitrate chemical modifier was used for thermal stabilization of the analyte in the electrothermal atomizer up to pyrolysis temperatures of 1300 °C, irrespective of the matrix. Quantitation of manganese was conducted in both cases by means of aqueous standards calibration. The detection limits were 0.3 and 0.4 ng ml⁻¹ for the slurry and the digested samples, respectively. The accuracy of the procedure was checked by comparing the results obtained in the analysis of slurries and digested brain samples, and by analysis of the NIST Bovine Liver standard reference material (SRM 1577a). The ease of slurry preparation, together with the conventional set of analytical and instrumental conditions selected for the determination of manganese make such methodology suitable for routine clinical applications.     

Characterization of peptides by liquid chromatography/electrospray ionization mass spectrometry using silver nitrate as a post-column complexant

Two model peptides, des-Arg1-bradykinin (DAB) and bradykinin (B), were cationized by Ag+ after their separation by reversed-phase liquid chromatography (RPLC) prior to mass spectrometry (MS). Silver nitrate solution was used as a post-column reagent. The RPLC and MS experimental conditions were optimized using flow injection in order to obtain sufficiently abundant silver adducts to permit MS/MS experiments. The use of water-methanol with 0.1% formic acid as mobile phase allowed a good chromatographic separation of the two peptides with a polymeric stationary phase and sufficiently abundant silver-containing adducts, [M + Ag + H]2+ and [M + 2Ag]2+. The gas-phase dissociation of [DAB + Ag + H]2+ and [DAB + 2Ag]2+ led to interpretable mass spectra during the on-line cationization experiment. Most of the ions obtained by dissociating [DAB + Ag + H]2+ and [DAB + 2Ag]2+ species are silver-containing ions but the ions produced depend on the parent. The ions coming from the dissociation of the doubly charged silver adducts [DAB + Ag + H]2+ or [DAB + 2Ag]2+ are of interest compared with those coming from the singly charged silver species or doubly charged protonated species. The fragmentation of the doubly charged silver adducts provides ions over the entire mass range. Although the presence of several prolines in des-Arg1-bradykinin prevents the formation of some expected ions, the observation of triplets [an-H + Ag]+, [bn-H + Ag]+ and [bn + OH + Ag]+ produced by the dissociation of on-line Ag(+)-cationized peptides could contribute to greater success of automatic sequencing of peptides.     

液-液萃取电感耦合等离子体质谱法测定天然水中痕量稀土元素

建立了以单、二（2－乙基己基）磷酸酯混合螯合剂的庚烷溶液作为萃取剂，6.0mol/L HCl反萃取预分离富集，In和Rh做内,ICP-MS测定天然水中15种稀土元素的分析方法。方法的富集倍数为200倍，各元素的检出限范围在0.01-1.8ng/L之间，相对标准偏差RSD＜5％，萃取回收率＞93％。     

Determination of clindamycin in animal plasma by high-performance liquid chromatography combined with electrospray ionization mass spectrometry

A method for the quantification of clindamycin in animal plasma using high-performance liquid chromatography combined with electrospray ionization mass spectrometry (LC/ESI-MS/MS) is presented. Lincomycin is used as the internal standard. The sample preparation includes a simple deproteinization step with trichloroacetic acid. Chromatographic separation is achieved on an RP-18 Hypersil column using gradient elution with 0.01 M ammonium acetate and acetonitrile as mobile phase. Good linearity was observed in the range 0-10 microg ml(-1). The limit of quantification of the method is 50 ng ml(-1) and the limit of detection is 1.3 ng ml(-1). The method was shown out to be of use for pharmacokinetic studies of clindamycin formulations in dogs.     

Mass transport in gas channels of electrochemical cells with a solid-oxide electrolyte: Allowing for the electrode reaction rates in numerical calculations

The concentration fields, Nusselt number distributions along the electrode, and ratios of concentrations of electrochemically active components at the entrance into and exit out of an electrochemical cell are determined by numerical integration of the convective-diffusion equation for a broad range of rate constants of electrode reactions, Peclet numbers, and geometrical parameters of channels. Three regions of parameter values are revealed. At low reaction rates (K _l < 0.5), mass transfer is completely determined by electrode kinetics; at high rates (K _l > 20), it is completely determined by the diffusion in the gas phase; and in the intermediate region of values of K _l it is necessary to allow for both the diffusion processes and the electrode reactions.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 317–324.Original Russian Text Copyright © 2005 by Ezin, Somov.     

气相色谱-质谱联用测定苯乙烯中的阻聚剂对叔丁基邻苯二酚

 建立了气相 质谱联用 (GC/MS)测定苯乙烯中阻聚剂对叔丁基邻苯二酚含量的方法。苯乙烯样品直接进样 ,通过毛细管柱 (HP 1,30m× 0 32mmi.d .× 0 2 5 μm)分离 ,由电子轰击 (EI)源于选择离子监测 (SIM)模式下进行检测。结果表明 ,对叔丁基邻苯二酚含量在 5mg/kg～ 5 0mg/kg时线性关系良好 (r2 =0 9987) ,回收率高 ;与美国材料测试标准ASTMD4 5 90中的分光光度测量法比较具有操作简捷、准确度高的特点。     

Investigation of homo- and heterodimer alkali metal cation complexes of resorc[4]arenes by electrospray ionization mass spectrometry

Resorc[4]arenes are compounds with interesting properties, mainly because of their ability to form host-guest complexes with the guest located inside the cavity. The size of the guest limits the complexation, as shown by a competition experiment with tetraalkylammonium ions of different size. By electroscopy ionization tandem mass spectrometric experiments on resorc[4]arene heterodimers bearing an alkali metal ion as guest, it was found that there must be two different binding mechanisms for alkali metal ions with high surface charge density (Li(+) and Na(+)) on the one hand compared with those with a lower surface charge density on the other hand (K(+), Rb(+), Cs(+)).     

成像技术在食品安全与质量控制中的研究进展

食品质量与安全是政府、食品行业以及消费者十分关注的问题。为了保证食品质量与安全，需要对食品中的风险因子进行检测。传统的分析方法如生物化学方法和仪器分析方法（色谱法、色谱-质谱法）存在前处理比较复杂，耗时，对样品具有破坏性及无法获取目标物空间信息等缺点。因此，开发快速，无损，实时和可视化的检测技术十分重要，这也是食品领域研究的热点。近年来，高光谱成像技术融合了成像和光谱两种技术，可以作为一种用于食品质量和安全评估的非破坏性和实时检测的工具。拉曼光谱成像技术可以同时获得待测物的光谱和空间信息，具有快速，无损和低成本等优点，在食品安全评价和质量控制中也得到了成功应用。质谱成像技术不需要标记和染色，即可实现样品组织表面待测物的可视化和高通量分析。它作为一种分子可视化技术，可以获得食品中营养成分及内、外源性有害物质的空间分布信息，在食品领域也表现出良好的应用前景。本文检索了近几年国内外发表的成像技术在食品研究中的相关文献，介绍了高光谱成像技术、拉曼光谱成像技术和质谱成像技术的原理，并综述了它们在食品安全与质量控制中的应用。此外，本文分析和讨论了这几种成像技术的优缺点，并对成像技术在食品领域的发展前景做出了展望。