Automated ultratrace determination of musty odiferous compounds from environmental waters by online purge and trap (P&T) gas chromatography–mass spectrometry (GC–MS)

Abstract

Odoriferous compounds are troublesome in natural waters in many parts of the world. The simultaneous determination of these complex compounds due to their low sample concentration and odor thresholds has been difficult. A simple, sensitive and automated technique for the determination of eight odoriferous compounds from aqueous samples was developed using online purge and trap (P&T) coupled to gas chromatography with mass spectrometry. P&T was selected to extract and purify the water samples. Several parameters that affect the extraction and concentration performance were investigated, including the trap sorbent, ionic strength, purge time, sample temperature and desorption time. Under the optimal conditions, the adsorption capacity for the Tenax TA sorbent to 2-isopropyl-3-methoxypyrazine, 4-chloroanisole, 2-isobutyl-3-methoxypyrazine, 2-methylisoborneol, 2-tert-butylphenol, 2,4-dichloroanisole, 2,4,6-trichloroanisole and geosmin reached an equilibration when sample volume was 25?ml at a concentration of 150.0?μg/l. The method provided good linearity in the range from 1.0 to1000?ng/l and the limits of detection were from 0.1 to 0.3?ng/l, which are below the odor thresholds for most of these compounds. The proposed method was applied to the determination of eight odoriferous compounds in surface and tap waters with recoveries from 74.7% to 112.8% and relative standard deviations from 2.6% to 10.8%. This method may be widely employed for monitoring odoriferous compounds in water samples.     

化学衍生物与GC/MS联用的进展(四)

3.0-异丙叉衍生物上面介绍的甲基化,乙酰化和三甲基硅基衍生物不能区分糖类异构体,而用0-异丙叉衍生物则可区分。因为这种衍生物的形成,依赖于羟基的空间排布,显著加大异构糖类的结构差别,得到不同的碎裂质谱。例如1,2:3,4—双—0—异丙叉—α—D—半乳吡喃糖(gala-ctopyranose)的主要断裂方式为:     

Chemical Assessment of Bottled Drinking Waters by IC,GC, and ICP‐MS

Abstract

Bottled water brands, consisting of both local and imported types, collected from Doha city, Qatar, were evaluated for their suitability for human consumption. Water quality constituents that were analyzed include trihalomethanes (THM) by GC‐ECD, turbidity, TDS, total hardness, total alkalinity, pH, EC, major anions by IC, and major cations and trace metals by ICP‐MS. The data obtained were compared with the WHO and the USEPA drinking water standards. As, Se, Ba, and Cu were undetected in all water samples. The levels of potential toxic metals in the studied brands were generally low, except for three brands that had Cd and Pb which exceeded the WHO limits. Fluoride was generally present in all bottled water brands at levels less than the lower optimum level. The reported data for pH, turbidity, TDS, EC, alkalinity, hardness, major anions, and major cations were generally in compliance with the WHO and the USEPA standards, with exception of five brands, where the levels of TDS, EC, F, and NO₃ exceeded the WHO recommended limits. Also, it was found that the concentrations of NO₃ F, Fe, Cr, Zn, and Pb were higher in the local brands. The levels of Cd, Mn, Ca, Mg, EC, alkalinity, SO₄, TDS, THM, and hardness were higher in the domestic brands, when compared to the imported ones. The levels of Cl, pH, turbidity, and Na in the domestic brands were comparable to imported ones. Three THM were found in 29% of water samples with three brands having CHCl₂Br and CHCl₃ levels exceeding the WHO standards.

Comparison of the results of this study with the reported label values of both domestic and imported bottled water showed good agreement with pH and K values, but significant variation for Ca, Mg, F, NO₃, and SO₄ in the imported brands and relatively low variation in the domestic brands. The results of chemical analysis of SRM 1460, trace elements in water, were generally in good agreement with NIST certified values.     

化学衍生物与GC/MS联用的进展(二)

7.双衍生化反应利用某些衍生试剂的选择性,采用组合的衍生试剂制备双衍生物。例如用组合的硅烷化试剂和N-酰基咪唑试剂,对儿茶酚胺(Catecholamine)中的羟基,首先与三甲基硅基咪唑(TMSIM)反应,然后氨基与七氟丁酰基咪唑反应,形成O-TMS/N-HFB衍生物。Domi-ke用选择的硅烷化和酰化反应,制备生物胺类的衍生物。反应如下:     

化学衍生物与GC/MS联用的进展(三)

对于有氨基的甲状腺激素及其类似物而言,ME—N,O—bis—HFB衍生物是最有用的。化合物1—4衍生物的质谱,有丰度强的M~+、(M-213)~+和(M-284)~+离子。即质谱中有显著的强丰度离子集中在高质量区,见T_4衍生物的质谱图(图3)。用(M-213)~+离子作SIM     

Linear stability analysis of Rayleigh-Bénard convection of cold water near its density maximum in a vertically heated annular container

In order to understand the onset of Rayleigh-Bénard convection of cold water near its density maximum in a vertical annular container heated from below and cooled from above, the instability of the static diffusive state was investigated by linear stability analysis. Two kinds of thermal boundary conditions, perfect insulating and conducting sidewalls, were used. The aspect ratio and radius ratio of the annular container varied from 0.5 to 4.5 and 0.1 to 0.8, respectively. Results indicate that the critical Rayleigh number and the critical wave number increase with the increase of density inversion parameter. There are some new flow modes with large azimuthal wave number near the convection onset for cold water with density maximum, which are not observed in Rayleigh-Bénard convection of the Boussinesq fluids. The stratified flow phenomenon in cold water with density maximum is certified. The larger the density inversion parameter is, the more obvious the stratified flow phenomenon becomes. With the increase of the aspect ratio, the critical Rayleigh number decreases, but the critical wave number increases. However, with the increase of the radius ratio, both the critical Rayleigh number and the critical wave number increase continuously. Furthermore, the effect of thermal boundary conditions at the sidewalls on the convection stability is also validated.     

Residue analysis of 500 high priority pesticides: Better by GC–MS or LC–MS/MS?

This overview evaluates the capabilities of mass spectrometry (MS) in combination with gas chromatography (GC) and liquid chromatography (LC) for the determination of a multitude of pesticides. The selection of pesticides for this assessment is based on the status of production, the existence of regulations on maximum residue levels in food, and the frequency of residue detection. GC-MS with electron impact (EI) ionization and the combination of LC with tandem mass spectrometers (LC-MS/MS) using electrospray ionization (ESI) are identified as techniques most often applied in multi-residue methods for pesticides at present. Therefore, applicability and sensitivity obtained with GC-EI-MS and LC-ESI-MS/MS is individually compared for each of the selected pesticides. Only for one substance class only, the organochlorine pesticides, GC-MS achieves better performance. For all other classes of pesticides, the assessment shows a wider scope and better sensitivity if detection is based on LC-MS.     

化学衍生化与GC/MS联用的进展(一)

八十年代有机质谱学的主攻方向是倾向于发展和研究生物—有机分子的新方法和新技术。     

Optimization of the linear quantification range of an online trypsin digestion coupled liquid chromatography–tandem mass spectrometry (LC–MS/MS) platform

Tandem mass spectrometry (MS/MS)-based proteomic workflows with a bottom-up approach require enzymatic digestion of proteins to peptide analytes, usually by trypsin. Online coupling of trypsin digestion of proteins, using an immobilized enzyme reactor (IMER), with liquid chromatography (LC) and MS/MS is becoming a frequently used approach. However, finding IMER digestion conditions that allow quantitative analysis of multiple proteins with wide range of endogenous concentration requires optimization of multiple interactive parameters: digestion buffer flow rate, injection volume, sample dilution, and surfactant type/concentration. In this report, we present a design of experiment approach for the optimization of an integrated IMER-LC–MS/MS platform. With bovine serum albumin as a model protein, the digestion efficacy and digestion rate were monitored based on LC–MS/MS peak area count versus protein concentration regression. The optimal parameters were determined through multivariate surface response modeling and consideration of diffusion controlled immobilized enzyme kinetics. The results may provide guidance to other users for the development of quantitative IMER-LC–MS/MS methods for other proteins.     

Optimization of pulsed laser atom probe (PLAP) for the analysis of nanocomposite Ti–Si–N films

Laser-assisted atom probe tomography was used to investigate the nanostructure and composition of high-performance, ultra-hard Ti–Si–N nanocomposite films. However, the quality of data is heavily dependent on analysis conditions. In order to obtain reliable data from these, and other ‘less conducting’ specimens, the analysis parameter space was thoroughly investigated to optimize the mass resolution and hit multiplicity obtained in atom probe tomography. Geometric factors including tip radius and shank angle were found to play a significant role in mass resolution but had no apparent effect on the number of multiple hits observed. Increased laser energy led to a gradual increase in the number of single hits, but a modest improvement in mass resolution. The influence of other instrumental factors including detection rate and base temperature was investigated separately. Preliminary PLAP results are presented, and correlated with TEM analysis of the microstructure of the film.     

鱼油中多氯联苯的气相色谱-质谱(GC/MS)分析

采用凝胶渗透色谱法 (GPC)和 Florisil土填充的 SPE小柱对鱼油样品进行净化处理 ,应用 GC/MS的分段选择性离子监测 (SIM)定性定量分析。结果表明 :SIM法可以定性分析鱼油实际样品中 3 1种多氯联苯 ,检测限为 1 0～ 1 0 0 fg,定量分析了其中的七种用来监测海洋受污染程度的多氯联苯     

以气相色谱仪——质谱计联用系统(GC/MS)分析痕量有机物

多年以来,环境研究科学家们一直很关心污染环境的一些特定有机化合物的鉴定及其浓度的测定。当需要知道具体污染物时,有机物污染的粗略测定[例如检验化学需氧量(COD),生化需氧量(BOD)以及总有机碳量(TOC)]就不够了。需要确切的鉴定,才能确定以下问题:     

安捷伦科技公司隆重推出新一代气质联用(GC/MS)系统 --5975 inert GC/MSD新产品发布会

2005年6月2日，安捷伦科技公司隆重推出新一代气质联用仪——Agilent 5975 inen GC／MSD。于6月13日，在北京友谊宾馆聚英厅召开了新产品5975 inen GC／MSD发布会暨技术讲座。参加本次会议的有来自各行业的分析工作者、专家学者和媒体记者等350余人。     

Construction and Evaluation of a Low Cost Interface for the Determination of Elemental Speciation by Gas Chromatography Coupled to Inductively Coupled Plasma Mass Spectrometry (GC‐ICP‐MS)

Abstract

The construction and evaluation of a low cost, easily demountable interface to couple capillary gas chromatography to inductively coupled plasma mass spectrometry detection is described. Using this interface, the capillary column can be maintained at a high temperature through to the tip of the torch injector using a transfer line heated by a combination of hot argon and electrical resistance. The interface is suitable for analytes with boiling points up to 230°C, allowing for the analysis of low and high boiling analytes in a single injection. The system was evaluated by the determination of the butyltin species in a marine sediment CRM using conventional calibration with tripropyltin dichloride as the internal standard and the measurement of methylmercury in a tuna fish CRM via species‐specific isotope dilution analysis. Detailed information on the design and construction of the interface are included to facilitate its construction and use by other workers.     

Nonlinearity and non-stationarity analysis of dynamic response of vehicle–track coupling system enhanced by Huang transform

A method is proposed to analysis the nonlinearity and non-stationarity of dynamic response of high speed vehicle–track coupling system, to understand the properties of signal and its underlying physical meaning. First, a space coupling model of high speed vehicle–track system is built according to the theory of coupling dynamics of vehicle–track system. Then, the dynamic response of vehicle–track system is processed by Ensemble Empirical Mode Decomposition (EEMD) to generate the intrinsic mode functions (IMFs). Next, the “Direct Quadrature” (DQ) method is used to calculate the local instantaneous frequency and instantaneous amplitude of the IMFs, the generalized zero-crossing method and the full wave zero-crossing method are applied to calculate the mean local frequency of the IMFs. Finally, the index and degree of nonlinearity and non-stationarity based on intra-wave frequency modulation (the deviation of the instantaneous frequency from the generalized zero-crossing frequency) and inter-wave frequency modulation (the deviation of the instantaneous frequency from the full wave zero-crossing frequency), are defined to quantify the nonlinearity and non-stationarity of dynamic response. The usefulness and capability of the proposed method are displayed through two cases, which are considered general enough to be the representatives of nonlinear and non-stationary dynamic response of vehicle–track coupling system.     

Multifractal analysis of Mg-doped ZnO thin films deposited by sol–gel spin coating method

A multifractal analysis has been performed on the 3D (three-dimensional) surface microtexture of magnesium-doped zinc oxide (ZnO:Mg) thin films with doping concentration of 0, 2, 4, and 5%. Thin films were deposited onto the glass substrates via the sol–gel spin coating method. The effect of magnesium doping, on the crystal structure, morphology, and band gap for ZnO:Mg thin films has been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–Vis spectroscopy. It has been observed that the surface of ZnO thin films is multifractal in nature. However, multifractality and complexity observed to decrease with increasing content of Mg in ZnO thin films due to formation of islands on the surface in accordance with Volmer–Weber growth mechanism. The investigations revealed that crystallinity, microtexture, morphology, and optical properties of the thin films can be tuned by controlling the Mg content within the ZnO lattice. In particular, their optical band gap energies were 3.27, 3.31, 3.34, and 3.33 eV at 0, 2, 4, and 5%, respectively. The prepared thin films of ZnO:Mg with tuned characteristics would have promising applications in optoelectronic devices.     

Further improved stability criteria for uncertain T–S fuzzy systems with time-varying delay by (m,N)-delay-partitioning approach

This paper mainly focuses on the robust stability criteria for uncertain T–S fuzzy systems with time-varying delay by (m,N)-delay-partitioning approach. A modified augmented LKF is established by partitioning the delay in all integral terms. Via taking into account of (i) the relationship between each subinterval and time-varying delay and (ii) the independent upper bounds of the delay derivative in the various delay intervals, some new results on tighter bounding inequalities such as Peng-Park׳s integral inequality and Free-Matrix-based integral inequality are introduced to effectively reduce the enlargement in bounding the derivative of LKF as much as possible, therefore, significant less conservative results can be expected in terms of e_s and LMIs, which can be solved efficiently with the Matlab LMI toolbox. Furthermore, it is worth mentioning that, when the delay-partitioning number m is fixed, the conservatism is gradually reduced with the increase of another delay-partitioning number N, but without increasing any computing burden. Finally, two numerical examples are included to show that the proposed method is less conservative than existing ones.