镍(Ⅱ)-丁二酮肟体系极谱催化波的机理研究

前文报道了钴(Ⅱ)-丁二酮肟(DMG)体系极谱催化波的机理,本文研究的是镍(Ⅱ)-DMG体系的行为.利用 Ni(Ⅱ)-DMG 极谱催化波测定痕量镍的方法在生物及岩矿石中应用较多,且可同时测定痕量镍、钴.对于这两个体系的机理,作者们也往往同时进行研究,但说法不一.迄今为止有四种说法.并且对镍和钴两催化波的异同,也未进行深入的研究.我们在研究Co(Ⅱ)-DMG 体系的同时,对 Ni(Ⅱ)-DMG 体系的机理也进行了较详细的对照的研究.     

金属-4-(2-吡啶偶氮)-间苯二酚(PAR)络合物的极谱研究(Ⅱ)——钼(Ⅵ)-PAR-NaClO3体系的极谱催化波

有关相络合物极谱催化波的报导颇多,但研究钼与PAR络合物极谱行为的工作尚未见报导。在稀硫酸(pH1.7)介质中,我们观察到,钼与PAR共存时产生一极谱还原波,再引入NaClO₃时,此波灵敏度增加,示波极谱导数波波形尖锐而又对称。本文研究钼(Ⅵ)-PAR-NaClO₅体系极谱催化波产生的条件,应用该体系测定了矿样中的痕量钼。     

铑(Ⅲ)与5-(5-氯-2-吡啶偶氮)-2,4-二氨基甲苯的配合物催化氢波研究

本文建立了一种催化极谱法测定痕量铑的新方法.先使铑(Ⅲ)与5-Cl-PADAT在pH5的HOAc-NaOAc缓冲溶液中生成稳定的配合物,再于适量HClO_4底液中进行极谱测定.并研究了影响极谱催化波的各种因素及波的性质,确定该波为铑(Ⅲ)与5-Cl-PADAT配合物的催化氢波,提出了可能的电极过程,并进行了实验验证.该法测定铑的线性范围为3.9×10~(12)—3.9×10~(-9)mol·dm~(-3),检出限为1.9×10~(-12)mol·dm~(-3).已应用于镍基合金及催化剂中铑的测定.     

用2-QADN2,7-金属络合物示波极谱法同时测定铜镍钴镉

本文研究了2-QADN2,7-金属络合物的极谱特性。在pH9.60的缓冲溶液中,Cu(Ⅱ)、Ni(Ⅱ)、Co(Ⅱ)和Cd(Ⅱ)与2-QADN2,7的络合物在-0.37、-0.69、-0.77和-0.82V产生灵敏的极谱波,利用这些波可测定痕量的铜、镍、钴和镉。铜的检测下限为2.0×10~(-8)mol/L,镍、钴及镉的检测下限为5.0×10~(-8)mol/L。提出的方法用于同时测定头发和茶叶中的痕量铜、镍和钴,结果满意。     

电化学分析法测定硒的研究进展

本文综述了国内外电化学分析(极谱和溶出伏安法)测定痕量硒的研究进展,主要包括极谱催化波、吸附波以及阴极溶出伏安法,阳极溶出伏安法,并从反应体系、催化波类型、检出限和电极反应机理等方面进行归纳与评述,展望了硒分析方法的研究方向和发展前景,对进一步研究硒的电化学性质和探索测定硒的新体系有重要参考价值。     

钴镍与1,2-环己烷二肟络合物的极谱催化波研究

在NaOH-1,2-环己烷二肟-NH₄Cl-NaNO₂体系中,钴镍均能产生灵敏的极谱催化波,在该体系中催化波的峰高与钴镍浓度成很好的线性关系,钴镍的最低检出极限分别为0.02和0.33ppb,对于1ppbCo和50ppb的Ni进行连续测定,其变更系数分别为±2.0％和±2.2％(n=10),本文详细地研究了形成Co、Ni催化波的条件,并初步探讨了机理,提出了可以同时测定痕量Co与Ni的分析方法。     

Ⅴ(Ⅴ)—3,5—Cl_2—DMPAP—NaBrO_3体系极谱催化波的研究及其应用

本文研究了V(V)—3.5—Cl_2—DMPAP—NaBrO_3体系极谱催化波产生的条件,探讨了波性质和反应机理,并拟定了示波催化极谱法测定矿样和钢样中痕量钒的分析方法。     

镍(Ⅱ)-硫代氨基脲体系的络合吸附波

利用Ni(Ⅱ)的络合吸附波测定微量镍,文献曾提出若干体系,但 Ni(Ⅱ)-硫代氨基脲(TSC)体系的络合吸附波尚未见报导。本文对该体系采用单扫示波极谱仪进行了试验,获得了灵敏的极谱波,并用多种方法探讨了该体系的机理,认为该极谱波是具有络合吸附波性质的催化前波。     

示波极谱法直接测定水中超痕量钨

本文对钨—溴邻苯三酚红极谱催化波进行了研究,发现体系中加入四乙基碘化铵后,极谱渡高明显增加,体系的稳定性显著提高,检出限达1.8×10~(-11)mol/L。确定了最佳条件,拟定了不经分离富集直接测定水中痕量钨的方法。此外还对极谱波性质进行了探讨,证明该极谱波为配合物吸附催化氢波,讨论了阳离子表面活性物质对催化氢波的作用机理。     

镍,钴与zincon的络合吸附波研究：铜精矿中微量镍,钴的同时测定

有关利用络合物的极谱催化波连续测定镍,钴的报道较少。在研究铜-Zincon的极谱行为时,我们发现NH_4Cl-Na_2SO_3(pH=6.5～7.5)底液中当Zincon浓度>4×10~(-5)·mol/L时,单扫描示波极谱仪上有两个峰,其峰电位分别为-0.42V和-0.56v(vs.     

钴(II)-丁二酮肟体系极谱催化波的机理研究

本文研究了钴(II)-丁二酮肟(DMG)在氨性底液(pH9)中极谱催化波的机理.用线性扫描伏安法,循环伏安法和阳极溶出法等方法证明,这催化波的形成是由于吸附在汞电极上的钴(II)-丁二酮肟螯合物不可逆地还原到零价的"活性钴",同时在电极表面的"活性钴"又催化了丁二酮肟的还原.     

钴(II)-丁二酮肟-亚硝酸盐体系极谱催化波的机理研究

在氨性底液(PH8)中, 钴(II)-丁二酮肟(DMG)-亚硝酸盐体系产生高灵敏的极谱催化波. 利用吸附伏安法, 测定下限可达1×10^-^1^1mol.dm^-^3Co. 我们用多种电化学方法和紫外可见分光光度法证明, 吸附在汞电极表面的[NH4]2[Co(DMG)2(NO2)2]是有很高电活性的混配化合物, 在复杂的电还原过程中, 不仅Co(II)和DMG被催化还原, 而且NO2^-也被催化还原, 从而产生很大的催化电流, 本文再一次证明, “活性钴"在催化波的形成过程中起着重要的作用.     

NH3/NH4Cl中镍(Ⅱ)-丁二肟体系在悬汞电极上电化学还原机理的研究

The behaviour of the Nickel(Ⅱ) ion in the presence of dimethyl-glyoxime (DMG) on the hanging mercury drop electrode in NH_3/NH_4Cl media was investigated with different electrochemical techniques. It was found that: (1) the reactant was Ni(Ⅱ) complex with DMG, Ni(Ⅱ)A_2, adsorbed on the electrode surface; (2) the intermediate was Ni(Ⅰ)A_2 and (3) the product was metal amalgam Ni(0)(Hg). Two electrons were transferred in the overall reaction and the transfer coefficient was 1.8 which was measured experimentally. From experimental results, it was obvious that the reaction orders with respect to Ni(Ⅱ), DMG and H~+ were 1,2, and 1, respectively. A new compound, X, was detected. The reaction scheme could be written as followsNi(Ⅱ)A_2+Hg<=>Ni(Ⅱ)A_2(ads)(Hg)Ni(Ⅱ)A_2(ads)(Hg)+e~-<=>Ni(Ⅰ)A_2(ads)(Hg)Ni(Ⅰ)A_2(ads)(Hg)+H~++e~-→Ni(0)(Hg)+HA(des)+A~-(des)→X+Hg     

Study on the polarographic catalytic wave of the system cobalt(II)-dimethylglyoxime

In the cobalt (II)-dimethylglyoxime-NH₃-NH₄Cl (pH 9) system, tne complex Co(II)A₂ exhibits a sensitive polarographic wave. The mechanism of this catalytic wave has been investigated by linear potential sweep voltammetry, cyclic voltammerty and anedic stripping voltammetry. The experimental evidences showed that a zero-valence “active cobalt” or its complex formed during the irreversible reduction of Co(II)A₂, which is adsorbed on the mercury electrode surface, and simultaneously DMG is catalytically reduced by this “active cobalt”. The mechanism of this system with the conflicting explanations of a catalytic hydrogen wave or only adsorptive complex wave is discussed.     

Selective determination of Ni(II) and Co(II) by flow injection analysis and adsorptive cathodic stripping voltammetry on a wall jet mercury film electrode

Ni(II) and Co(II) have been determined simultaneously by means of adsorptive cathodic stripping voltammetry (AdCSV) in a computerised flow injection system. The working electrode was a glassy carbon disk that was fitted in a wall-jet flow cell. The electrode was initially electrochemically coated with a mercury film at -1.0 V by injecting a Hg(II) solution in the flow stream. Then, the sample, containing Ni(II) and Co(II), was mixed on-line with a solution containing dimethylgyoxime (DMG) at pH 9 in order to selectively complex the metal ions and was injected in the flow system. After a number of successive injections during which accumulation took place under controlled potentiostatic conditions, the surface-bound complexes were reduced in ammonia buffer at pH 9 by a cathodic scan of the potential of the working electrode in the square wave mode and the current-potential response was recorded. Finally, the electrode surface was regenerated by a potentiostatic polarisation at -1.4 V in the same buffer. The apparatus could be easily converted for continuous flow accumulation in order to increase the sensitivity; in this mode of operation, instead of performing discrete injections, the sample was continuously pumped through the cell. Various parameters associated with the preconcentration, stripping and regeneration steps were optimised for the determination of Ni(II) and Co(II). The selectivity of the method was demonstrated for the analysis of high purity iron; the accuracy for the determination of Ni(II) and Co(II) was 11 and 3%, respectively while the coefficient of variation was 10 and 8%, respectively.     

四元缔合物体系薄层树脂相分离与光度法联用测定痕量钴

提出了在酸性条件下 (pH=5.0),利用阳离子交换树脂-丁二酮肟-碘-钴四元体系,通过薄层树脂相光度法测定钴的新方法。本法灵敏度高 (e454=1.7105L/molcm),比水相光度法提高14倍,精密度理想 (测定2.0礸/ml Co(II) 6次,RSD=1.3%),选择性好。实测药品VB12及天然水中钴,线性范围0.024~2.0礸/ml (定容50ml),检出限10.4ng/ml。     

Simultaneous determination of nickel(II) and cobalt(II) by square wave adsorptive stripping voltammetry on a rotating-disc bismuth-film electrode

This works reports the use of square-wave adsorptive stripping voltammetry (SWAdSV) for the simultaneous determination of Ni(II) and Co(II) on a rotating-disc bismuth-film electrode (BFE). The metal ions in the non-deoxygenated sample were complexed with dimethylglyoxime (DMG) and the complexes were accumulated by adsorption on the surface of the BFE. The stripping step was carried out by using a square-wave potential-time voltammetric excitation signal. Electrochemical cleaning of the bismuth film was employed, enabling the same bismuth film to be used for a series of measurements. The experimental variables (choice of the working electrode substrate, the presence of oxygen, the DMG concentration, the buffer concentration, the preconcentration potential, the accumulation time, the rotation speed and the SW parameters) as well as potential interferences were investigated and the figures of merit of the methods were established. Using the selected conditions, the 3σ limits of detection were 70 ng l⁻¹ for Co(II) and 100 ng l⁻¹ for Ni(II) (for 300 s of preconcentration) and the relative standard deviations were 2.3% for Co(II) and 3.9% for Ni(II) at the 2 μg l⁻¹ level (n = 8). Finally, the method was applied to the determination of nickel and cobalt in real samples with satisfactory results.     

Catalytic Adsorptive Stripping Chronopotentiometry of Co(II)‐DMG‐Bromate System at an In Situ Plated Lead Film Electrode

A novel catalytic adsorptive stripping chronopotentiometric (CC‐CAdSCP) procedure for the determination of Co(II) traces was developed using a lead film electrode (PbFE). The PbFE was generated in situ on a glassy carbon support from a 0.1 M ammonia buffer containing 1×10^?5 M Pb(II), 6.5×10^?5 M DMG and the target metals. An addition of 0.2 M NaBrO₃ to the solution yielded an 11‐fold catalytic enhancement of chronopotentiometric response of the Co(II)‐DMG complex. The CC‐CAdSCP curves were well‐developed, sharp and reproducible (RSD 5.0 % for 5×10^?9 M Co(II)). The limit of detection for Co(II) for 210 s of accumulation time was 4×10^?10 M (0.024 µg L^?1). In addition, the elaborated method allowed the simultaneous quantification of Co(II) and Ni(II) simultaneously.     

Simultaneous Adsorptive Cathodic Stripping Voltammetric Determination of Nickel(II) and Cobalt(II) at an In Situ Bismuth‐Modified Gold Electrode

A study on the simultaneous determination of Ni(II) and Co(II) dimethylglyoximates (Ni‐DMG and Co‐DMG) through adsorptive cathodic stripping voltammetry at an in situ bismuth‐modified gold electrode (Bi‐AuE) is reported. The key operational parameters, such as Bi(III) concentration, accumulation potential and accumulation time were optimized and the morphology of the Bi‐microcrystals deposited on the Au‐electrode was studied. The Bi‐AuE allowed convenient analysis of trace concentrations of solely Ni(II) or of Ni(II) and Co(II) together, with cathodic stripping voltammograms characterized by well‐separated stripping peaks. The calculated limit of detection (LOD) was 40 ng L^?1 for Ni(II) alone, whereas the LOD was 98 ng L^?1 for Ni(II) and 58 ng L^?1 for Co(II), when both metal ions were measured together. The optimized method was finally applied to the analysis of certified spring water (NIST1640a) and of natural water sampled in the Lagoon of Venice. The results obtained with the Bi‐AuE were in satisfactory agreement with the certified values and with those provided by complementary techniques, i.e., ICP‐OES and ICP‐MS.     

Ligand displacement, headspace single-drop microextraction, and capillary electrophoresis for the determination of weak acid dissociable cyanide

A new method involving ligand displacement, headspace single-drop microextraction (SDME) with in-drop derivatization and capillary electrophoresis (CE) was developed for the determination of weak acid dissociable (WAD) cyanide. WAD metal-cyanide complexes (Ag(CN)(2)(-), Cd(CN)(4)(2-), Cu(CN)(3)(2-), Hg(CN)(2), Hg(CN)(4)(2-), Ni(CN)(4)(2-) and Zn(CN)(4)(2-)) are decomposed with ligand-displacing reagent and the released hydrogen cyanide is extracted from neutral solution (pH 6.5) with an aqueous microdrop (5 microl) containing Ni(II)-NH(3) as derivatization agent. The hydrogen cyanide extracted reacts with Ni(2+) to form a stable and highly UV absorbing tetracyanonickelate anion which is then determined by CE. Among the three different ligand-displacing reagents (i.e., ethylenediamine, dithizone and polyethileneimine) studied none of the reagents used alone releases cyanide completely from all WAD cyanide complexes. Complete recoveries were obtained by the extraction of WAD cyanide from 0.4 mol l(-1) ethylenediamine chloride buffer (pH 6.5) containing 0.001% (wt) dithizone. Proposed system was applied to determine WAD cyanide in industrial wastewater and river waters samples with spiked recoveries in the range of 95.8-104.7%.