Speciation of selenium(IV) and selenium(VI) in environmental samples by the combination of graphite furnace atomic absorption spectrometric determination and solid phase extraction on Diaion HP-2MG

A simple solid phase extraction procedure for speciation of selenium(IV) and selenium(VI) in environmental samples has been proposed prior to graphite furnace atomic absorption spectrometry. The method is based on the solid phase extraction of the selenium(IV)-ammonium pyrrolidine dithiocarbamate (APDC) chelate on the Diaion HP-2MG. After reduction of Se(VI) by heating the samples in the microwave oven with 4 mol l⁻¹ HCl, the system was applied to the total selenium. Se(VI) was calculated as the difference between the total selenium content and Se(IV) content. The experimental parameters, pH, amounts of reagents, eluent type and sample volume were optimized. The recoveries of analytes were found greater than 95%. No appreciable matrix effects were observed. The adsorption capacity of sorbent was 5.20 mg g⁻¹ Se (IV). The detection limit of Se (IV) (3sigma, n = 11) is 0.010 μg l⁻¹. The preconcentration factor for the presented system was 100. The proposed method was applied to the speciation of selenium(IV), selenium(VI) and determination of total selenium in natural waters and microwave digested soil, garlic, onion, rice, wheat and hazelnut samples harvested various locations in Turkey with satisfactory results. In order to verify the accuracy of the method, certified reference materials (NIST SRM 2711 Montana Soil, NIST SRM 1568a Rice Flour and NIST SRM 8418 Wheat Gluten) were analyzed and the results obtained were in good agreement with the certified values. The relative errors and relative standard deviations were below 6 and 10%, respectively.     

Faster GC analyses performed by flow programming in short capillary columns

The technique of programming the carrier gas flow rate in gas chromatography, especially in connection with the use of capillary columns shorter than 10 m can significantly accelerate GC analyses. Equations for calculation of the parameters of the exponential flow function and retention data are described. The effects of flow programming in a short capillary column are shown in a few chromatograms. Different programming rates are tested and compared with temperature programming.     

Packings and stationary phases for biopolymer separations by HPLC

Summary Packings and stationary phases applied to high resolution separations of proteins, enzymes, and nucleic acids must satisfy a series of distinct criteria that are different from those usually required by HPLC of low molecular weight non-biologically active analytes. These requirements have been met through substantial improvements in classical gel media together with novel developments in silica supports, and have led to a family of products with tailor-made and reproducible properties. Supports consisting of cross-linked organic gels, and inorganic materials (mostly silicas) are now available with graduated particle sizes, pore sizes, porosities and surface areas as well as non-porous beads. A whole range of stationary phases, such as reversed phase, hydrophobic interaction, ion exchanger and affinity packings, were designed for application as chemical sensors for biopolymer recognition in adsorptive chromatography. The phase systems are operated in the gradient mode, giving high resolution and high peak capacities. In addition, aqueous liquid-liquid partitioning systems have been developed for the fractionation of proteins and nucleic acids. Size exclusion media complete the set of HPLC variants enabling a discrimination of proteins according to their size and shape in an isocratic elution mode. Basically, protein purification and isolation is a multistage process where-by the HPLC variants are combined in a logistic sequence, utilizing the different selectivities of the phase systems and thus maximising resolution, speed and throughput.     

缬氨酸产品中微量氨基酸杂质的高效阴离子交换色谱-积分脉冲安培测定

在优化实验条件下,建立了高效阴离子交换色谱-积分脉冲安培检测法分离测定缬氨酸产品中微量氨基酸杂质的方法。研究了氨基酸的阴离子交换色谱分离和积分脉冲安培检测。采用优化的水、0.25 mol/LNaOH、1.0 mol/L NaAc三元梯度淋洗条件及35℃柱温实现了19种氨基酸的分离。在最佳条件下,氨基酸的检出限(S/N=3)为3.1~67.1 nmol/L,线性范围约为3个数量级。样品加标回收率为90%~96%。方法可以推广至其它氨基酸产品中微量氨基酸杂质的测定。     

N，N-二丁基癸酰胺萃取硝酸有机相结构研究

利用界面张力、电导、FT-IR等研究了不同硝酸浓度下萃取有机相的微结构。利用Gaussian曲线拟合处理N，N-二丁基癸酰胺(DBDEA)的羰基吸收峰，结果表明体系中存在多种以氢键结合的物种如DBDEA·HNO₃、(DBDEA)₂·HNO₃等。在较高酸度下有机相中萃取剂分子自组装成小的聚集体-反相胶团，极性核由水、硝酸和萃取剂高电荷密度的极性部分构成。     

Simultaneous operation of plural separation modes in capillary electrophoresis with a chemiluminescence detector possessing a micro-space area for reaction/detection

Analysis of alpha-amino acids, proteins, and phenolic compounds was simultaneously performed using three capillaries in capillary electrophoresis with chemiluminescence detection, taking advantage of the micro-space area for reaction/detection at the tip of the capillary. The three capillaries included usual, polymer-containing, and sodium docley sulfate (SDS)-containing migration buffers for separation. The eluted samples from the capillaries, which were inserted into the chemiluminescence detection cell, were mixed with chemiluminescence reagent at the tips of the capillaries to generate visible light. The specific micro-space area for reaction/detection at the tips of the capillaries enabled the simultaneous operation of the three separation modes in the present system.     

Crystallite Nanosize Effect on the Structural Transitions of WO3 Studied by Raman Spectroscopy

Nanocrystallites of tungsten oxide samples of 2, 4, 16, 35 and 60 nm of diameter were prepared by cryosol and pyrosol techniques. The pressure- and temperature-induced phase transitions of these samples were monitored by Raman spectrometry from 0.1 MPa to 34 GPa and from 77 to 1200 K. The tetragonal (α)-orthorhombic (β)-monoclinic (γ) transitions in these nanometric samples are strongly downshifted in temperature by comparison with the bulk WO₃. For instance, the tetragonal phase which exists above 1171 K for the bulk tungsten oxide can be stabilized at 700 K for the 35 nm sample. In the same way, the monoclinic P2₁/n-monoclinic P2₁/c high-pressure-induced transition is slightly shifted from 0.1 GPa to a higher pressure (1.5 GPa). The discussion of these transition-line shifts is based on thermodynamic considerations in which the surface energy of crystallites plays an important role.     

基质固相分散气相色谱电子捕获检测器测定葡萄酒中5种农药残留

采用基质固相分散的样品前处理方法,替代传统的液-液萃取、固相萃取,从葡萄酒中提取、净化5种农药,气相色谱电子捕获检测器分析测定,基质匹配标准校正方法补偿基质效应。添加3水平(0.01-0.10mg/L)的回收率为85.7%-104.6%;相对标准偏差为3.6%-8.5%;检出限达到0.1-0.8μg/kg。本方法可用于葡萄酒样品中农药残留的测定。     

对甲苯磺酸三甲胺固定相的研究及其分析应用

采用汞塞动态法涂柱,以对甲苯磺酸三甲胺作为固定液制备了石英毛细管色谱柱,固定液量为9.0%(m/V),柱尺寸为30 m×0.32 mm i.d.。对该柱的性能进行了考察。实验结果表明,这种色谱固定相对于极性有机化合物如醇类物质、有机羧酸、酚类物质等有良好的分离能力,且出峰快,时间短,峰形窄而对称。