Determination of thiol compounds by solid-phase extraction using multi-walled carbon nanotubes as adsorbent coupled with high-performance liquid chromatography-fluorescence detection

Microchimica Acta - We describe a method for solid-phase extraction of biogenic thiols using multi-walled carbon nanotubes as adsorbent, and their subsequent determination via HPLC and fluorescence...     

静电位阻模型在纳滤膜跨膜电位解析中的应用

采用静电位阻模型对纳滤膜的跨膜电位进行了理论解析, 考察了溶液体积通量密度、原料液浓度、阴阳离子扩散系数比、膜孔半径和膜体积电荷密度对KCl(1-1型电解质)和MgCl2(2-1型电解质)中的纳滤膜跨膜电位的影响. 研究结果表明, 随着通量密度的增大, KCl和MgCl₂的跨膜电位线性程度增强; 两种电解质的跨膜电位均随着原料液浓度和膜孔半径的增大而下降; 在不同的考察范围内, 阴阳离子扩散系数比对1-1型和2-1型电解质的跨膜电位的影响差别较大; KCl的跨膜电位随着膜体积电荷密度的变化关于零点呈现出对称性, 而MgCl₂的跨膜电位零点则出现在膜体积电荷密度为负的条件下.     

Sensitive Determination of Thiols Using SPE Coupled to LC with Fluorescence Detection

The purpose of the present work is to develop a simple, rapid, sensitive and accurate method for the derivatization and subsequently preconcentration of Hg(II) and the determination of its derivative, diphenylmercury, in natural water samples using gas chromatography-flame ionization detection. The method is based on the diphenylation using phenyl boronic acid, subsequent extraction of phenylmercury into a single drop of an organic solvent (toluene), followed by gas chromatography-flame ionization detection GC-FID analysis of the extract. The pH of the feed solution was kept in pH 5 with acetate buffer solution. Thus, the optimized conditions are: organic solvent, toluene; derivatization time, 10 min; extraction time, 15 min; microdrop volume, 1.6 μL; stirring rate, 600 rpm; sample volume, 5 mL. The limit of detection (LOD), calculated on the basis of five replicates was 0.02 μg mL^?1. The relative standard deviation of the method (RSD%, n = 5) was 3.0. Linear range was between 0.05 and 5 μg mL^?1 and preconcentration factor obtained for phenyl-mercury was 105.     

Asymmetric (4+n) Cycloadditions of Indolyldimethanols for the Synthesis of Enantioenriched Indole-Fused Rings

Catalytic asymmetric construction of chiral indole-fused rings has become an important issue in the chemical community because of the significance of such scaffolds. In this work, we have accomplished the first catalytic asymmetric (4+2) and (4+3) cycloadditions of 2,3-indolyldimethanols by using indoles and 2-naphthols as suitable reaction partners under the catalysis of chiral phosphoric acids, constructing enantioenriched indole-fused six-membered and seven-membered rings in high yields with excellent enantioselectivities. In addition, this approach is used to realize the first enantioselective construction of challenging tetrahydroindolocarbazole scaffolds, which are found to show promising anticancer activity. More importantly, theoretical calculations of the reaction pathways and activation mode offer an in-depth understanding of this class of indolylmethanols. This work not only settles the challenges in realizing catalytic asymmetric cycloadditions of indolyldimethanols but also provides a powerful strategy for the construction of enantioenriched indole-fused rings.     

Study on transmembrane electrical potential of nanofiltration membranes in KCl and MgCl2 solutions

The transmembrane electrical potential (TMEP) across two commercial nanofiltration membranes (ESNA1-K and Filmtec NF) was investigated in KCl and MgCl(2) solutions. TMEP was measured in a wide range of salt concentrations (1-60 mol·m(-3)) and pH values (3-10) at the feed side, with pressure differences in the range of 0.1-0.6 MPa. A two-layer model based on the Nernst-Planck equation was proposed to describe the relation between TMEP and permeation flux. From the pattern of these curves, the information of membrane structure could be deduced. In the concentration range investigated, TMEP in KCl solutions was always positive and decreased as the salt concentration increased. The contribution of the membrane potential to the TMEP decreased. TMEP was greatly affected by the feed pH. When the feed pH increased, the mobility of cations increased, which indicated that the charges of NF membranes were more negative. The zero point of TMEP and the minimum of rejection in KCl solution were consistent and occurred at the isoelectric point of NF membranes, while in MgCl(2) solution the zero point of TMEP located at a higher pH value. The TMEP in MgCl(2) solutions changed its sign at a given concentration, and by calculating the transport number the location of the minimum rejection could be determined.     

Free energies of the ion equilibrium partition of KCl into nanofiltration membranes based on transmembrane electrical potential and rejection

The free energies of ion equilibrium partition between an aqueous KCl solution and nanofiltration (NF) membranes were investigated on the basis of the relationship of the transmembrane electrical potential (TMEP) and rejection. The measurements of TMEP and rejection were performed for Filmtec NF membranes in KCl solutions over a wide range of salt concentrations (1-60 mol·m(-3)) and pH values (3-10) at the feed side, with pressure differences in the range 0.1-0.6 MPa. The reflection coefficient and transport number, which were used to obtain the distribution coefficients on basis of irreversible thermodynamics, were fitted by the two-layer model with consideration of the activity coefficient. Evidence for dielectric exclusion under the experimental conditions was obtained by analyzing the rejection of KCl at the isoelectric point. The free energies were calculated, and the contribution of the electrostatic effect, dielectric exclusion, steric hindrance, and activity coefficient on the ion partitioning is elucidated. It is clearly demonstrated that the dielectric exclusion plays a central role.     

Novel electrochemical sensor based on functionalized graphene for simultaneous determination of adenine and guanine in DNA

A nano-material carboxylic acid functionalized graphene (graphene-COOH) was prepared and used to construct a novel biosensor for the simultaneous detection of adenine and guanine. The direct electrooxidation behaviors of adenine and guanine on the graphene-COOH modified glassy carbon electrode (graphene-COOH/GCE) were carefully investigated by cyclic voltammetry and differential pulse voltammetry. The results indicated that both adenine and guanine showed the increase of the oxidation peak currents with the negative shift of the oxidation peak potentials in contrast to that on the bare glassy carbon electrode. The electrochemical parameters of adenine and guanine on the graphene-COOH/GCE were calculated and a simple and reliable electroanalytical method was developed for the detection of adenine and guanine, respectively. The modified electrode exhibited good behaviors in the simultaneous detection of adenine and guanine with the peak separation as 0.334V. The detection limit for individual determination of guanine and adenine was 5.0×10(-8)M and 2.5×10(-8)M (S/N=3), respectively. Furthermore, the measurements of thermally denatured single-stranded DNA were carried out and the value of (G+C)/(A+T) of single-stranded DNA was calculated as 0.80. The biosensor exhibited some advantages, such as simplicity, rapidity, high sensitivity, good reproducibility and long-term stability.     

Field desorption mass spectrometry: I. Cyclic nucleotides

The FD spectra of nineteen 3′, 5′-cyclic nucleotides and their derivatives are reported. The principal features of spectra, the fragmentation mode, and the experimental techniques are described.     

Electron ionization and field desorption mass spectrometry of some macrocyclic crown ether-lactones

The electron impact (ED mass spectra of fourteen macrocyclic crown ether-lactone (involving aliphatic and aromatic groups) were reported, and some typical EI fragmentation patterns were discussed in detail with the aid of exact mass measurement, linked scan and defocussing technique. The features of the field desorption (FD) mass spectra of ten compounds were also summarized.     

LC Determination of Thiols Derivatized with 4-(Aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole after SPE

Solid-phase extraction (SPE) coupled with high-performance liquid chromatography?Cfluorescence detection (LC?CFL) was developed for the determination of three thiol compounds including glutathione, cysteine and acetylcysteine. 4-(Aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole was used for derivatization of thiols. Factors affecting derivatization and extraction efficiency were optimized. Sample solution (2?mL) was extracted on a SPE column for 2?min and then eluted with 400???L methanol. The analytes were injected onto the LC system for separation on a C₁₈ column, and eluted with methanol?Cacetate buffer. The analytes were detected by fluorescence at an emission wavelength of 515?nm with excitation at 385?nm. The linearity of the method was in the range of 0.1?C60???M, with correlation coefficients ranging from 0.9979 to 0.9990. The detection limits of the method were in the range of 5?C20?nM. The proposed method was applied to the analysis of human plasma samples with recoveries of 86?C112.9%.