Multiphoton-Ionization-Mass Spectrometry (MUPI-MS) [New Analytical Methods (34)]

Mass spectrometry is one of the most important analytical tools in chemistry, biology, medicine and related areas. During the past 30 years, methods have been developed, both for the qualitative as well as the quantitative analysis of a wide variety of substances. The introduction of lasers into chemistry has also profited mass spectrometry, since its nonlinear properties and its tunability open up fundamentally new frontiers. Multiphoton ionization mass spectrometry combines UV-spectroscopy and mass spectrometry, thus providing a two-dimensional method that enables substance-specific and even state-specific analyses. This progress report presents the fundamentals and possibilities of MUPI mass spectrometry and discusses investigations on amino acids, peptides, chlorophylls and sugars. For each substance, multiphoton ionization can be tuned in such a way that only the molecular ion is formed. An increase of laser intensity induces substance-specific fragmentations of the molecule, thus contributing to a quick and easy identification of the substance.     

The optimal amount of isotopic spike solution for ultratrace analysis by isotope dilution mass spectrometry

 Inductively coupled plasma mass spectrometry (ICP-MS) and high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) are powerful methods of determining metallic impurities in the low- and sub-ppt level in process media such as ultra-pure water used in semiconductor and wafer manufacturing. By using mass spectrometers for analysis, an isotope dilution analysis (IDMS) is possible. The reproducibility of an IDMS is unmatched. For concentration levels near the instrument detection limit a novel method is reported to find the optimal amount of isotopic spike solution. This optimal value can be derived by the law of propagation of uncertainty combined with the Poisson statistics of the measured number of counts. Generally, an excess of isotopic spike solution should be used to provide results of lowest possible uncertainty. The results are presented in a diagram for easy practical use. Received: 14 October 1997 · Accepted: 13 February 1998     

Selenomethionine contents of NIST wheat reference materials

Values of the total selenium and selenomethionine (Semet) content of four wheat-based reference materials have been obtained by gas chromatography-stable isotope dilution mass spectrometry methods. The total Se method is an established one, and the results obtained with it are consistent with previously-assigned values. The Semet method (previously reported by our laboratory) is based on reaction with CNBr. Our data indicate that the four wheat samples (wheat gluten, durum wheat, hard red spring wheat, and soft winter wheat), though having a 30-fold range in total Se content, all have about 45% of their total Se values in the form of selenomethionine. Investigation of the CNBr-based method suggests that additional experiments are needed to verify that all selenomethionine in the wheat samples is accounted for, but also indicates that the values obtained are within 15% of the true values. As the form in which Se occurs in foods and dietary supplements is important from a nutritional perspective, adding information about Se speciation to total Se values in appropriate reference materials makes these materials more valuable in relevant analytical work.     

毛细管电泳质谱联用技术及其应用

本文介绍了用于毛细管电泳质谱联用仪器的多种接口技术，描述了ＣＺＥ，ＣＩＥＦ，ＣＧＥ，ＭＥＫＣ和ＣＩＴＰ等毛细管电泳技术和四极质谱，离子阱质谱，傅 叶变换离子回旋共振质谱，飞行时间质谱，磁质谱，解吸质谱等联用的现状及发展前景，对近年来ＣＥ－ＭＳ在酶解产物。蛋白质和肽，核苷酸，药物及代谢产物等领域中的应用作了详细述评。     

Modified modeling of the effect of pH and viscosity on the mass transfer in hydrophobic hollow fiber membrane contactors

This paper studied the effect of pH and the viscosity of feed solution on the mass transfer in two different specifications of hydrophobic hollow fiber membrane contactors. Experimental results showed that the pH of the feed had a significant effect on the rate of mass transfer, the flux and the removal efficiency of easily ionized volatile compounds (VCs), such as ammonia. In unbuffered feed solutions, both the resistance of membrane and the resistance of feed side were affected by the pH of feed and both of them had contributions to the overall mass transfer. A model, , was proposed to predict the effect of pH and gave good agreement with the experimental data for the two contactors. The relationship between viscosities and the mass transfer coefficient could be described by . Based on our experiments, the change of the viscosities in the concentration range of ammonia from 50 to 10,000 mg l⁻¹ caused about 3–4% variation of the mass transfer coefficients. Moreover, it may be more suitable to use the equilibrium concentrations of volatile species instead of the total concentrations of VCs to estimate mass transfer coefficients, removal efficiency and flux. Experimental results also revealed that the choice of the pH of feed might be one of the most crucial factors for removing easily ionized VCs, such as ammonia, from water and wastewater.     

2-芳基硫杂脯氨酸结构特征的研究

对12种2-芳基硫杂脯氨酸进行了红外光谱和核磁共振谱测定,对其中两个化合物作了质谱测定。结果表明,这类化合物固态时主要以两性离子形式存在;有较强的分子离子峰,是一类较稳定的化合物。它们还存在一对非对映异构体,芳环上的取代基对芳环电子云密度的影响较大,而对四氢噻唑环的影响较小。     

兴奋剂检测中的化学衍生化方法

本文评述了兴奋剂检测中的各种化学衍生化方法,对蛋白同化激素、麻醉镇痛剂、β-阻断剂和利尿剂分别进行了讨论。这四类药物结构各不相同,但绝大多数属于高沸点、难挥发的极性化合物,不适于直接进行GC或GC/MS分析。通过化学衍生化.不仅可增大试样的挥发性和稳定性,减小样品的极性,使原来难以进行GC分析的试样转变成适合于色谱分析的试样,而且通过衍生化还可达到改善分离效果、提高检测灵敏度的目的。     

Two-dimensional protein database of human pancreas

We report here the two-dimensional protein database of human pancreas. The proteins were analyzed by two-dimensional electrophoresis followed by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Totally, 302 proteins were identified, of which about 27% were enzymes with a broad range of catalytic activities. Several of these are specifically expressed in pancreas, such as pancreatic amylase, pancreatic stone protein, pancreatitis-associated protein, pancreatic lipase, pancreatic elastase, etc. Structural and cytoskeletal proteins are also strongly represented on the gels. Thus, the pancreatic proteome reflects the organ's function. This work paves the way for further studies on pancreatic protein expression in health and disease, such as diabetes and pancreatic cancer.     

一种利用质谱信息进行结构特征鉴定的模式识别方法

本文提出了分段式离子系列谱编码方法,实验证明具有很好的结构表征能力。本程序主要是以模式识别技术为基础,实现了对未知物谱图的KNN分类,进而得到未知物的主要结构特征。这个程序应用于有机化合物的分类,取得了满意的结果。     

Capillary electrophoretic determination of lignin degradation products obtained by permanganate oxidation

A new capillary electrophoretic (CE) technique was developed for the separation of lignin degradation products after permanganate oxidation, yielding information about quality and quantity of various linkages in the lignin molecule. This CE method is a promising alternative to existing gas chromatographic (GC) methods. An advantage in comparison with GC is the short separation time and the fact that the oxidation products (aromatic acids) can be analyzed without derivatization. The selectivity and sensitivity of CE combined with UV detection is adequate and makes it suited for fast routine characterization of lignins. If necessary, the CE method can be coupled with electrospray ionization mass spectrometry in order to make a clear assignment of the peaks.