Trace lead measurement and on-line removal of matrix interference in seawater by isotope dilution coupled with flow injection and ICP-MS

Isotope dilution analysis method coupled with flow injection and inductively coupled plasma mass spectrometry (ID-FI-ICP-MS), enabled trace lead concentration in seawater to be determined and the high salt concentration in the matrix, such as Na⁺, Ca²⁺ and Mg²⁺, to be removed on-line. The operational parameters of the FI system including pH for the chelating reaction, concentration of 8-hydroxyquinoline-5-sulfonic acid (8-HQS), sample loading time and injection speed, washing time and speed, eluting acid concentration and eluting speed, and instrumental parameters for ICP-MS were optimized and selected. Accurate results could be achieved because the isotope ratios required can be precisely measured in the range of the eluting peak by means of ID-FI-ICP-MS. The 3σ detection limit was 0.204 ng ml⁻¹. The trace lead concentration of seawater in south Xiamen, China was 0.988 ± 0.039 ng ml⁻¹. The recoveries of spiked Pb standard in seawater and standard reference water (GBW 08607) were 97.9 and 101.0%, respectively, with a relative standard deviation of 0.98%. This method can be used to determine trace lead concentration in high salt matrix samples, and is especially useful when the eluting peaks do not have a Gaussian-distribution.     

Sensitive Voltammetric Response of p‐Nitroaniline on Single‐Wall Carbon Nanotube‐Ionic Liquid Gel Modified Glassy Carbon Electrodes

An ionic liquid (i.e., 1‐butyl‐3‐methylimidazolium hexafluorophosphate, BMIMPF₆)‐single‐walled carbon nanotube (SWNT) gel modified glassy carbon electrode (BMIMPF₆‐SWNT/GCE) is fabricated. At it the voltammetric behavior and determination of p‐nitroaniline (PNA) is explored. PNA can exhibit a sensitive cathodic peak at ?0.70 V (vs. SCE) in pH 7.0 phosphate buffer solution on the electrode, resulting from the irreversible reduction of PNA. Under the optimized conditions, the peak current is linear to PNA concentration over the range of 1.0×10^?8–7.0×10^?6 M, and the detection limit is 8.0×10^?9 M. The electrode can be regenerated by successive potential scan in a blank solution for about 5 times and exhibits good reproducibility. Meanwhile, the feasibility to determine other nitroaromatic compounds (NACs) with the modified electrode is also tested. It is found that the NACs studied (i.e., p‐nitroaniline, p‐nitrophenol, o‐nitrophenol, m‐nitrophenol, p‐nitrobenzoic acid, and nitrobenzene) can all cause sensitive cathodic peaks under the conditions, but their peak potentials and peak currents are different to some extent. Their peak currents and concentrations show linear relationships in concentration ranges with about 3 orders of magnitude. The detection limits are 8.0×10^?9 M for p‐nitroaniline, 2.0×10^?9 M for p‐nitrophenol, 5.0×10^?9 M for o‐nitrophenol, 5.0×10^?9 M for m‐nitrophenol, 2.0×10^?8 M for p‐nitrobenzoic acid and 8.0×10^?9 M for nitrobenzene respectively. The BMIMPF₆‐SWNT/GCE is applied to the determination of NACs in lake water.     

A Pair of Novel Heptentriol Stereoisomers from the Ascomycete Daldinia concentrica

A pair of novel heptentriol stereoisomers, hept‐6‐ene‐2,4,5‐triols 2 and 3 , were isolated from the culture broth of the ascomycete Daldinia concentrica (Bolton : Fries ) Cesati & De Notaris , besides three known compounds, i.e., 2,3‐dihydro‐5‐hydroxy‐2‐methyl‐4H‐1‐benzopyran‐4‐one ( 1 ), 3,5‐dihydroxy‐2‐(1‐oxobutyl)‐cyclohex‐2‐en‐1‐one ( 4 ), and pyroglutamic acid (=5‐oxo‐L ‐proline; 5 ). Their structures were determined by spectroscopic means, including 2D‐NMR (HMQC, HMBC, ¹H,¹H‐COSY).     

Structure of Palladium( Ⅱ ) Complex with 2-Hydroxy-propane 1, 3-diamine-N,N,N'''' N'''',-tetraacetic Acid

The reaction of PdCl2 in water with 2-hydroxypropane-1, 3-diaminetetraacetic acid (HPDTA) gave the complex Pd (C11H16N2O9)·1. 5H2O, which was characterized by elemental analysis, IR, NMR and single-crystal X-ray diffraction. The spectroscopic and X-ray diffraction data show that Pd ( Ⅱ ) is coordinated by two nitrogen atoms and two car-boxylic oxygen atoms. The complex crystallizes in monoclinic space group Pc with a = 1. 1240(2), b=1. 1183(2), c=1. 2597(3) nm, β=96. 33(2)°V=1. 5737(6) nm3, Z = 4, R= 0.038. The structure contains two crystallographically independent molecules which have slightly different orientations and are connected by hydrogen bonds.     

Cyclic Voltammograms of Ferrocene on Multi‐Walled Carbon Nanotubes (MWCNTs)‐Modified Edge Plane Pyrolytic Graphite (EPPG) Electrode in Room Temperature Ionic Liquids (RTILs) of 1‐Ethyl‐3‐Methylimidazolium Tetrafluoroborate (EMIBF4)

In this work, the electrochemical behavior of ferrocene (Fc) was investigated by cyclic voltammetry (CV) in room temperature ionic liquids (RTILs) of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIBF₄) on glass carbon (GC), edge plane pyrolytic graphite (EPPG) and multi‐walled carbon nanotube (MWCNTs)‐modified EPPG electrodes, respectively. The results demonstrated that on GC electrode, pairs of well‐defined reversible peaks were observed, while for the electrode of EPPG, the peak potential separation (ΔE_p) is obviously larger than the theoretical value of 59 mV, hinting that the electrode of EPPG is distinguished from the commonly used electrode, consistent with the previous proposition that EPPG has many “defects”. To obtain an improved electrochemical response, multi‐walled carbon nanotubes (MWCNTs) were modified on the electrode of EPPG; the increased peak current and promoted peak potential separation not only proved the existence of “defects” in MWCNTs, but also supported that “creating active points” on an electrode is the main contribution of MWCNTs. Initiating the electrochemical research of Fc on the MWCNTs‐modified EPPG electrode in RTILs and verifying the presence of “defects” on both EPPG and MWCNTs using cyclic voltammograms (CVs) of Fc obtained in RTILs of EMIBF₄, is the main contribution of this preliminary work.     

Nitrile-functionalized pyridinium ionic liquids: synthesis, characterization, and their application in carbon-carbon coupling reactions

A series of relatively low-cost ionic liquids, based on the N-butyronitrile pyridinium cation [C(3)CNpy](+), designed to improve catalyst retention, have been prepared and evaluated in Suzuki and Stille coupling reactions. Depending on the nature of the anion, these salts react with palladium chloride to form [C(3)CNpy](2)[PdCl(4)] when the anion is Cl(-) and complexes of the formula [PdCl(2)(C(3)CNpy)(2)][anion](2) when the anion is PF(6)(-), BF(4)(-), or N(SO(2)CF(3))(2)(-). The solid-state structures of [C(3)CNpy]Cl and [C(3)CNpy](2)[PdCl(4)] have been established by single-crystal X-ray diffraction. The catalytic activity of these palladium complexes following immobilization in both N-butylpyridinium and nitrile-functionalized ionic liquids has been evaluated in Suzuki and Stille coupling reactions. All of the palladium complexes show good catalytic activity, but recycling and reuse is considerably superior in the nitrile-functionalized ionic liquid. Inductive coupled plasma spectroscopy reveals that the presence of the coordinating nitrile moiety in the ionic liquid leads to a significant decrease in palladium leaching relative to simple N-alkylpyridinium ionic liquids. Palladium nanoparticles have been identified as the active catalyst in the Stille reaction and were characterized using transmission electron microscopy.     

Transition metal substituted tungstophosphoric compound catalyzed oxidation of hexanol to hexanal with hydrogen peroxide

Summary The oxidation of hexanol in the presence of the Keggin-type heteropoly compounds (HPCs) H₃PMo_nW_12-nO₄₀ (denoted as PMo_nW_12-n, n=0,1) and Na₅PW₁₁ZO₃₉ (denoted as PW₁₁Z, Z = Mn, Fe, Co, Ni, Cu and Zn) was carried out to produce hexanal and hexanoic acid. The reaction was conducted in tert-butanol (t-BuOH), using cetylpyridinium bromide (CPB) salts of HPA and 15% aqueous H₂O₂ as oxidant under mild condition. The PMoW₁₁ catalyst showed higher hexanol conversion of 25%, the lowest selectivity to hexanal of 64.4% and an efficient utilization of H₂O₂ of 34%. Over the transition metal substituted PW₁₁Z catalysts decomposition of H₂O₂ was rapid. For these PW₁₁Z catalysts, the efficient utilization of H₂O₂ decreased to 9% or even lower. By means of IR, UV-visible and GC-MS techniques the catalysts were characterized.     

苯乙烯基氮氧杂芳烃间的交叉光二聚反应

用中压汞灯(λ > 300 nm)照射4-苯乙烯基吡啶、2-苯乙烯基苯并噁唑和5-苯基-2-苯乙烯基噁唑三种杂芳基乙烯单体中任意两种的硫酸水溶液，得到三种交叉二聚体.用高效液相色谱跟踪研究了交叉光二聚反应，发现每组反应生成三种光二聚体，其中二种为单体自身的光二聚体，而另外一种是两种不同单体的交叉光二聚体.交叉二聚体通过柱色谱分离得到，其顺式头对尾结构经紫外、红外、氢谱、碳谱和元素分析确定.用紫外光谱和高效液相色谱跟踪研究了交叉光二聚体的稀溶液在低压汞灯（λmax=254 nm）照射下的光解反应.研究发现交叉二聚体能够彻底发生光解，首先生成原来的反式单体，所生成的反式单体容易发生异构化而生成顺式单体，最终建立起反顺异构化平衡.     

The influence of cetyltrimethyl ammonium bromide on electrochemical properties of thyroxine reduction at carbon nanotubes modified electrode

The effect of cetyltrimethyl ammonium bromide (CTAB) on the electrochemical behaviors of thyroxine at a glassy carbon electrode (GCE) modified with single-walled carbon nanotubes (SWNTs) was investigated. At the SWNTs film-coated GCE, a well-defined oxidation peak of thyroxine at 0.78 V was obtained, but the reduction peak of thyroxine was indiscernible. When trace CTAB was added to the working solution, the reduction current could be greatly enhanced and the oxidation current remained stable. The reaction mechanisms for the reduction of thyroxine were explored by chronocoulometry. Thyroxine might form particular ion complex with CTAB via the interaction between iodine atoms on thyroxine and bromide ions in CTAB, which made the concentration of thyroxine at the surface of the modified electrode increased and the electron transfer rate enhanced. The proper mechanisms for the enhanced reduction of thyroxine in the present of CTAB were explored by several electrochemical techniques including cycle voltammetry linear sweep voltammetry and others. It was concluded that the special interactions between the thyroxine CTAB and SWNTs resulted in the increase of the reduction peak current. All results indicated that two iodine atoms on the thyroxine and four electrons were involved the reduction process which was irreversible and two iodine ions produced. In this system, the sensitive reduction peak of thyroxine at 0.3 V was employed to determine thyroxine and a low detection limit of 2x10(-8) mol/L was obtained for 2 min accumulation at 0.9 V. The SWNTs coated GCE had good stability and reproducibility.