Double threshold behaviour of I－V characteristics of CoSi2/Si Schottky contacts

The forward current－voltage (I－V) characteristics of polycrystalline CoSi₂/n-Si(100) Schottky contacts have been measured in a wide temperature range. At low temperatures (≤200K), a plateau-like section is observed in the I－V characteristics around 10^-4A·cm^-2. The current in the small bias region significantly exceeds that expected by the model based on thermionic emission (TE) and a Gaussian distribution of Schottky barrier height (SBH). Such a double threshold behaviour can be explained by the barrier height inhomogeneity, i.e. at low temperatures the current through some patches with low SBH dominates at small bias region. With increasing bias voltage, the Ohmic effect becomes important and the current through the whole junction area exceeds the patch current, thus resulting in a plateau-like section in the I－V curves at moderate bias. For the polycrystalline CoSi₂/Si contacts studied in this paper, the apparent ideality factor of the patch current is much larger than that calculated from the TE model taking the pinch-off effect into account. This suggests that the current flowing through these patches is of the tunnelling type, rather than the thermionic emission type. The experimental I－V characteristics can be fitted reasonably well in the whole temperature region using the model based on tunnelling and pinch-off.     

Influence of relaxation effects on probabilities of the 2s2p35S2－2s22p2 3P1，2 intercombination transitions in NII

Transition probabilities of the 2s2p^3 {}^5S_2－2s^22p^2 {}^3P_{1,2} intercombination transitions in NII have been calculated by using a large-scale multiconfiguration Dirac－Fock method. In the calculation the most important effects of relativity, correlation, and relaxation are considered. From the calculated transition probabilities, the lifetime of the 2s2p^3 {}^5S_2 metastable state is derived. The result is in excellent agreement with the latest experimental result. In the meantime the influence of anomalously strong relaxation effects on probabilities of the 2s2p^3 {}^5S_2－2s^22p^2 {}^3P_{1,2} lines in NII have been found.     

HPLC测定祖师麻注射液中祖师麻甲素的含量

采用HPLC测定祖师麻注射液中祖师麻甲素的含量,选用VPODSC18(4.6mm×150mm,5m)色谱柱,流动相为乙腈-0.5%的醋酸水溶液(28∶72),柱温30℃,流速1.0mL/min,检测波长326nm,祖师麻甲素在0.1498—1.3478mg·mL-1范围内浓度与其峰面积呈良好的线性关系,该方法简便、准确、重现性好。     

RP-HPLC同时测定饮料中安赛蜜、阿斯巴甜及苯甲酸

建立了一种同时检测几种饮料中安赛蜜、阿斯巴甜及苯甲酸的高效液相色谱检测方法。确定了最佳色谱条件:色谱柱:Diamonsil-C₁₈（250mm×4.6mm,5μm）;流动相:0.02mol/L硫酸铵:乙腈:磷酸=80:20:0.02（V/V/V）;流速:1.0mL/min;紫外检测器检测波长:210nm。该方法加标回收率在94.5%—101.5%之间,精密度小于3%。实现了对碳酸饮料、茶饮料及橙汁中的安赛蜜、阿斯巴甜及苯甲酸的同时测定。     

HPLC测定那西肽预混剂中那西肽的含量

建立了高效液相色谱法(HPLC)测定那西肽预混剂中那西肽含量。采用Shim-pack vp-ODS色谱柱(150mm×4.6mm,5μm),流动相为乙腈-0.025%磷酸水(52∶48),流速为1.0mL/min,检测波长为241nm,柱温为35℃。那西肽在6.127—36.763μg/mL范围内线性关系良好,线性方程为y=51410x+2418.3,r=0.9996,平均回收率为99.32%,RSD=0.77%。本方法简便、快速、重复性好,可用于那西肽预混剂的质量控制。     

4-(5-溴-2-噻唑偶氮)间苯二酚反相阳离子对HPLC测定痕量铌、钒、铑、铬

本文报道新试剂4-(5-溴-2-噻唑偶氮)间苯二酚(5-Br-TAR)为柱前衍生试剂,以阳离子表面活性剂作为对离子试剂,用含15 mmol／L的pH 5.8的乙酸-乙酸钠缓冲溶液、0.05 mmol／L溴化钠、10 mmol／L TBA·Br的乙腈-甲醇-水(42 : 13：45,V／V／V)三元体系为流动相,在C8柱上25min内HPLC测定了Nb(V)、V(V)、Rh(Ⅲ)和Cr(Ⅵ)的5-BR-TAR螯合物。当SNR=2时,检出限分别为Nb(V)1.0、V(V)1.6、Rh(Ⅲ)0.9和Cr(Ⅵ)1.9μg／L。该方法用于测定污水中的铬和钒,结果良好。     

Determination of the residue of quizalofop-p-tefuryl in soybean by HPLC

A HPLC method was developed for the analysis of quizalofop-P-tefurylof in soybean. The samples were extracted with methanol-water (volume ratio), The extracts were cleaned up with a column of silica gel. The final residue was detected by HPLC, using a UV detector. The recoveries from the analytical method for soybean were 84.32%–89.25%. Variable coefficients were 0.49%∼1.51%. This method proved to be simple, reliable and accurate. __________ Translated from Chinese Journal of Chromatography, 2005, 23(2)(in Chinese)     

Capillary HPLC–ICP MS mapping of selenocompounds in spots obtained from the 2-D gel electrophoresis of the water-soluble protein fraction of selenized yeast

A method based on ICP collision-cell MS detection in capillary HPLC was developed to gain an insight into the purity and identity of selenium-containing proteins separated by 1-D and 2-D electrophoresis. The bands and spots obtained after the separation of water-soluble proteins in selenized yeast were digested with trypsin prior to chromatography. Selenium could be detected down to the subpicogram level. The method, assisted by information obtained by MALDI TOF MS on the 5000 Da cut-off fraction, permitted the purity of bands and spots to be estimated and the efficiency of tryptic digestion and the quantity of selenium present in individual peptides to be evaluated. Owing to the high sensitivity and the lack of matrix suppression effects, the method provided chromatograms with signal-to-noise ratios of 10–1000 in conditions where the common ES Q–TOF MS detection failed.      

Investigation of copper-azamacrocyclic complexes by high-performance liquid chromatography

The use of copper radioisotopes in imaging and therapy has prompted an increased interest in chelators which form stable copper complexes, such as Cu(II)-azamacrocyclic complexes. The effects of charge, stability and the size of the macrocyclic backbone of the Cu(II)-azamacrocyclic complexes on biological behavior have been evaluated. Here we report a reversed-phase high-performance liquid chromatography (HPLC) method to separate several Cu(II)-azamacrocyclic complexes, including Cu(II) complexes of 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA), 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (CB-TE2A) and 4,10-bis(carboxymethyl)-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (CB-DO2A). Absorbance at 280 nm was used to monitor the complexes as they eluted from the reversed-phase column. The effects of the concentration of the buffer, the pH of the buffered mobile phase and the concentration of the organic modifier, methanol, on the separation were investigated. Separation of these copper complexes by ion-pair HPLC with the use of a mass spectrometry-compatible ion-pair reagent, triethylammonium acetate, in the mobile phase at pH 6.3 is also presented. The reversed-phase chromatographic conditions utilized also allow the pK(a)s of Cu-TETA and the log(k'w) values of Cu-CB-TE2A, Cu-TETA and Cu-CB-DO2A to be estimated.     

Determination of acyclovir in horse plasma and body fluids by high-performance liquid chromatography combined with fluorescence detection and heated electrospray ionization tandem mass spectrometry

Two methods are presented for the determination of 'respectively' the plasma protein unbound and total concentration of acyclovir in horse plasma and body fluids: first, a liquid-liquid extraction was performed on plasma, combined with HPLC-fluorescence detection for the total plasma concentration; second a more sensitive method using high-performance liquid chromatography combined with heated electrospray ionization tandem mass spectrometry (LC-HESI-MS/MS) was described for plasma and for body fluids analysis. To obtain the unbound concentration of acyclovir in plasma, a simple deproteinization step using a Microcon filter was performed. Ganciclovir was used as an internal standard. Analysis was carried out on an Inertsil 5 ODS-3 column for the HPLC-fluorescence method. For the LC-HESI-MS/MS method a PLRP-S column was used. The limit of quantification (LOQ) for the total concentration was set at 50 and 2 ng mL(-1) for the HPLC-fluorescence method and the LC-HESI-MS/MS method, respectively. The limit of quantification for the unbound concentration was set at 5 ng mL(-1) and at 2 ng mL(-1) for body fluids. The methods were successfully used to perform pharmacokinetic and clinical studies in horses after intravenous and oral dosage of acyclovir and its prodrug valacyclovir.