Calibration graphs in isotope dilution mass spectrometry

Isotope-based quantitation is routinely employed in chemical measurements. Whereas most analysts seek for methods with linear theoretical response functions, a unique feature that distinguishes isotope dilution from many other analytical methods is the inherent possibility for a nonlinear theoretical response curve. Most implementations of isotope dilution calibration today either eliminate the nonlinearity by employing internal standards with markedly different molecular weight or they employ empirical polynomial fits. Here we show that the exact curvature of any isotope dilution curve can be obtained from three-parameter rational function, y = f(q) = (a₀ + a₁q)/(1 + a₂q), known as the Padé[1,1] approximant. The use of this function allows eliminating an unnecessary source of error in isotope dilution analysis when faced with nonlinear calibration curves. In addition, fitting with Padé model can be done using linear least squares.     

Phase behavior of ionic liquids 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides with halogenated benzenes

(Liquid + liquid) miscibility temperatures as a function of composition have been determined experimentally for the binary systems formed by imidazolium based ionic liquids with bis(trifluoromethylsulfonyl)imide ([C_nMIM][NTf₂]: n = 3 to 10) with fluorobenzene, chlorobenzene, bromobenzene, iodobenzene and 1,2-dichlorobenzene. In addition, the phase diagrams for deuterated chlorobenzene, bromobenzene and 1,2-dichlorobenzene have been obtained. All the measured systems show the limited miscibility with the upper critical solution temperature behavior. Similarly to the other systems with the imidazolium cation the increase of the alkyl chain length in this cation improves the miscibility. The impact of the halogenobenzene is also very visible. The miscibility is improving in the order: iodobenzene < bromobenzene < chlorobenzene < fluorobenzene. This arrangement corresponds to the decreasing molar volume of the substituted benzenes. The disubstituted chlorobenzene is a better solvent for ionic liquids than chlorobenzene. The replacement of hydrogen for deuterium in halogenobenzenes in all cases improves the miscibility and the isotope shifts of the UCSTs are very large.     

使用态-态分辨的量子波包方法对Li+HF/DF反应的研究

使用基于反应物坐标的含时量子波包方法,在APW势能面上,计算了碰撞能在0～0.25 eV范围的Li+HF/DF(v=0,j=0,1)反应的积分和微分截面．同时也计算了初始态选择的反应速率常数．计算结果表明,Li+DF和Li+HF反应产物分布基本类似,只是前者产物转动激发态稍微多些．反应物的转动激发对于Li+DF反应影响很小．这两个反应的微分截面都是前向散射为主的,特别是在碰撞能较高时候．产物振转态分辨的积分截面和后向散射随碰撞能而呈现的振荡现象,可以用来指认Li+HF反应中的共振态．Li+HF的反应速率常数在100～300 K几乎不变,而Li+DF的反应速率常数则增长了10倍左右．Li+HF的反应几率和积分截面和以前报道的结果总体符合较好,差别应该是计算收敛性更好所致．     

Global status of trace elements in the ocean

Trace elements in seawater can be limiting factors of biological productivity, tracers of ocean circulation and biogeochemical processes, and proxies for paleoceanography. The global status of trace elements and their isotopes (TEIs) in the ocean is being explored this decade through an international study of the global marine biogeochemical cycles of TEIs (GEOTRACES). Such an international study has become possible due to recent methodological developments in sampling, preconcentration, and measurement of TEIs. Here, we present an overview of recent methodological developments and initial GEOTRACES intercalibration activities for obtaining data about TEIs that are accurate, precise, and intercomparable.     

Lithium transport within the solid electrolyte interphase

A LiClO₄ SEI film grown on copper was examined with time-of-flight secondary ion mass spectrometry. The SEI porosity profile and Li⁺ transport processes within the SEI were studied with isotopically labeled ⁶LiBF₄ electrolyte. An ~ 5 nm porous region, into which electrolytes can easily diffuse, was observed at the electrolyte/SEI interface. Below the porous region, a densely packed layer of Li₂O and/or Li₂CO₃ prevents electrolyte diffusion, but Li⁺ transports through this region via ion exchange.     

Application of isotope dilution mass spectrometry to research of certified reference materials

This paper briefly describes the method and applications of isotope dilution mass spectrometry(IDMS). Primary standard solutions with various natural isotope abundances were used to certify the concentration of enriched isotope solutions by IDMS. Then these enriched isotopes were used to certify unknown samples by IDMS. Li, K, Mg, Fe, Cu, Ni, Cd, Mo, Pb, etc in CRMs were certified and very good results were obtained in three international comparisons by IDMS. Received: 15 June 2000 Accepted: 26 October 2001     

Isotope shift measurement of high-lying atomic levels by multi-step photoionization

A new technique has been developed to measure isotope shifts of high-lying atomic levels using multi-step photoionization. This technique has been demonstrated with the measurement of isotope shift between²³⁵U and²³⁸U isotopes in the energy level at 34372.992 cm⁻¹. The value of isotope shift thus measured matches well with the value reported in literature.     

天然丰度氘核磁共振测定一级和二级动力学氘同位素效应(Ⅲ)——对Grignard试剂水解反应的应用

本文报道了用天然丰度~2HNMR测定一级动力学氘同位素效应的方法。这种方法与现有方法不同,它要求在反应时授氢反应物大大过量于受氢底物,在计算时要考虑由~2HNMR测定的反应物和产物的特定部位同位素比率(D/H):或化合物的平均同位素比率(D/H)。我们用这种方法研究了一些Grignard试剂水解的同位素效应。     

Application of hyphenated techniques to the chromatographic authentication of flavors in food products and perfumes

This work presents two techniques for testing for the adulteration of flavors. One uses multidimensional gas chromatography on cyclodextrin derivatives to separate chiral compounds, the other uses isotope ratio mass spectrometry coupled with gas chromatography to determine stable isotope ratios. Applications to fruits and plants for the food and perfume industry are introduced.