Invetigations into the use of an auxiliary metal ion for indirect amperometri detection

Summary A method for determination of metal ions subsequent to separation by ion chromatography has previously been developed. The method is based on Indirect Amperometric Detection whereby the decrease in the oxidation current, due to a dithiocarbamate ligand added post column, is monitored. Upon elution from the chromatographic column the metal ions are complexed by the ligand. As the complexes formed are electroinactive at the applied potential, the background current decreases according to the metal ion concentration. The method developed in this work involves addition to the reagent of Zn(II) as a auxiliary metal ion to displace the analyte metals from the chromatographic eluent ligand complexes after separation. Sodium bis(2-hydroxy-ethyl) dithiocarbamate was used as the postcolumn derivatising reagent. The addition of Zn(II) to the reagent causes some unforeseen behaviour in the chromatographic system.     

Silica gel-immobilized Eriochrome black-T as a potential solid phase extractor for zinc (II) and magnesium (II) from calcium (II)

The immobilization of silica gel surface with Eriochrome black-T indicator (ERT) for the formation of silica-ERT phase is described. The surface coverage of silica gel, based on carbon and nitrogen analysis of the modified silica gel phase, is 0.38 mmol g(-1). The stability towards hydrolysis of silica-ERT phase in different buffer solutions (pH 1-10) is studied and evaluated. The applicability of silica-ERT as a solid phase extractor for Zn(II), Mg(II) and Ca(II) is studied by the batch equilibrium technique and found to show an order similar to the formation constant values of these three metal ions with the indicator. The selectivity of silica-ERT phase towards the extraction of a certain metal ion from a mixture containing only two metal ions is studied by the batch equilibrium technique and exhibited good discrimination orders for Zn(II) and Mg(II) in presence of Ca(II). The results of the column separation and preconcentration studies are consistent with the selectivity behaviour of silica-ERT phase, thus affording reasonable separation of the three studied metal ions.     

Determination of protonation- and metal complex stability constants for a chelating monomer and its immobilized in polymer resin

An improved method is described for the calculation of complex stability constants for metal–ligand complexes considering ligands immobilized in resin phase. The applicability of it has been proved for N′-benzylethylene diamine N,N,N′-triacetic acid monomer (BEDTA) and for the ion exchange resin developed in the authors laboratory immobilizing this with styrene divinyl benzene. Calcium and magnesium metal ion complexes were investigated. Electrochemical and flame photometric measurements were used to collect equilibrium concentration data. The procedure worked out included the measurement of the quantity of resin bound water. Using these and the other experimentally gathered values and the improved way of calculation metal ligand complex stability constants were determined in aqueous media. Ion exchange chromatographic separation of calcium and magnesium ions was performed with a resin containing column for separation and optimized eluent.     

Preparation and characterization of monoliths covalently bonded chelating groups for capillary electrochromatographic separation of metal ions

In this work, a novel polymer-based monolithic column was prepared using an o-phthalaldehyde-l-phenylalanine Schiff base complex as the reactive center and a mixture of methanol and n-propanol as the porogen. The monolithic column was employed for the separation of a metal ion mixture including Pb(II), Mn(II), Cu(II), Ni(II), Cr(III), Fe(III) and Cr(VI). Tetrabutylammonium bromide (TBAB) was used as a mobile phase additive to enhance the separation efficiency of metal ions by EDTA precomplexation. Using a phosphate buffer (20 mM, pH 3.0), TBAB (10 mM), MeOH (15%, v/v), an applied voltage of −15 kV, and detection at 220 nm, the metal ion mixture was satisfactorily resolved. The average theoretical plate number was 17,900 plates/m. The separation was also carried out in the absence of TBAB, leading to dissimilar elution order and shorter retention time. The separation behavior of the monolithic column was also compared with that of the blank polymer. The unique properties of the monolithic column might be mediated by a combination of electrophoretic behavior and chromatographic retention involving hydrophobic and hydrophilic interactions, as well as ligand exchange.     

Selectivity behaviour of a bonded phosphonate--carboxylate polymeric ion exchanger for metal cations with varying eluent compositions

The chromatographic behaviour of a commercially available ion-exchange stationary phase (the Dionex IonPac CS12A column) is described for a wide range of transition and heavy metal ions with nitric acid eluents containing chloride and nitrate potassium salts. The separation selectivity was found to arise from simultaneous ion-exchange interactions and chelation with the attached carboxylic and phosphonic acid groups. These interactions were investigated by altering the ionic strength and pH of the eluent and also the column temperature. Strong affinity of the stationary phase towards heavy metal ions, in particular bismuth and the uranyl ion was observed at low pH under chelating ion-exchange conditions, with high efficiency separations of other ions including cadmium and lead being possible with short analysis times (approximately 5-15 min). Examples are given of separations obtained using 4-(2-pyridylazo)resorcinol or Arsenazo III as the post-column chromogenic reagents, demonstrating the potential versatility and utility of this stationary phase for heavy metal ion analysis.     

Separation of metal ions and metal-containing species by micellar electrokinetic capillary chromatography, including utilisation of metal ions in separations of other species

The use of micellar electrokinetic capillary chromatography (MEKC) for the separation of metal ions and metal-containing species is reviewed, together with the use of metal ions as a means to separate other species. Topics covered include the manipulation of separation selectivity through the use of complexation reactions induced by addition of a metal ion to the background electrolyte, enantiomeric separations facilitated through metal-analyte interactions, separation of organometallic species, separation of stable metal complexes in which the entire complex is the analyte and the separation of metal ions as analytes using pre-capillary or on-capillary complexation reactions with a suitable ligand.     

Separation selectivity of anionic metal complexes of N,N'-bis(hydroxybenzyl)ethylenediamine-N,N'-diacetic acid in ion and ion electrokinetic chromatography

The complexes of Fe(III), Co(III), Mn(III), Al(III), Cu(II), Ni(II), Cd(II) and Zn(II) with N,N'-bis(hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) were separated by ion exchange in different modes: ion chromatography (IC) and ion electrokinetic chromatography (IEKC). In column IC these complexes were separated on an IonPac AS4a anion-exchange column (Dionex, USA). Parameters of the background electrolyte that were examined in IEKC mode include polymer, competing ion concentration and pH. The use of poly(diallyldimethylammonium chloride) (PDADMACl) as a modifier in IEKC provides separation selectivity only slightly different from that observed in IC on the IonPac AS4a column. Optimal separation conditions were found to be: 0.1 mM HBED, 50 mM PDADMAOH, 10 mM Na2 B4 O7, pH adjusted to 10 with acetic acid. The use of an aromatic ligand allowed a 10-fold decrease in detection limits of metal ions in comparison with previously studied EDTA. A separation efficiency up to 400,000 theoretical plates was demonstrated for IEKC.     

Retention Behavior of Proteins on Glutamic Acid-Boned Silica Stationary Phase

A glutamic acid-bonded silica (Glu-silica) stationary phase with cation-exchange properties was synthesized using l-glutamic acid as ligand and silica gel as matrix. The effects of solution pH value, salt concentration and metal ion on the retention of proteins were examined. The standard protein mixture was separated with a prepared chromatographic column and an iminodiacetic acid column, and compared. The influence of the binding capacity of an immobilized metal ion on the complexation of metal chelate column was studied. The results indicate that the obtained column displays cation-exchange characteristic and better separation ability for proteins. As fixing metal ion on the Glu-silica column, retention of proteins on the column is a cooperative interaction of metal chelate and cation-exchange. The stationary phase shows the typical metal chelate properties with the increase of the sorption capacity of immobilized metal ion.     

Separation of Neutral Amino Acids with Ligand Exchange Resins

Four neutral amino acids (Gly, Ala,.Val and Leu) were separated with ligand exchange resins. The separation capacity of the ligand exchange resins is compared with that of common ion exchange resins. The effects of eluent, column temperature, and central metal ions of the support on the separation are studied. The relationship between matrix structure of resins and their separation capacity is analysed.     

Dissociation of gas-phase dimeric complexes of lactic acid and transition-metal ions formed under electrospray ionization conditions; the role of reduction of the metal ion

Dimeric complex ions of the type [M(A-H)A]+, where M=metal ion (Co, Ni, Cu, and Zn) and A=ligand (lactic acid, methyl lactate or ethyl lactate), were generated in the gas phase under electrospray ionization conditions. The collision-induced dissociation spectra of [M(A-H)A]+ ions were recorded to study the behaviour of ligand and metal ions in decomposition of these dimeric complex ions. Based on the fragmentation pathways observed for complex ions of lactic acid, it is found that both the carboxylic and hydroxyl groups of lactic acid are involved in the complex formation following displacement of a proton by the metal ion. The dimeric complex ions of Co, Ni, and Zn dissociated to yield similar types of ions, whereas that of Cu behaved differently. The dissociations of Co-, Ni-, and Zn-bound dimeric complexes involved losses of neutral molecules while keeping the oxidation state of the metal ion unchanged. However, elimination of radicals is found in the dissociation of dimeric complex ions of Cu, and the oxidation state of copper is reduced from Cu(II) to Cu(I) in the resulting fragment ions. The deprotonated ligand is involved in the fragmentation pathway of Cu complexes, whereas it is intact in other complexes. The oxidation state of the metal ion, nature of the ligand, and site of attachment to the metal ion are found to control the dissociation of these dimeric complex ions.     

Ligand-exchange chromatography of carbohydrates and glycoconjugates

The current status of ligand-exchange chromatography (LEC) is reviewed in the light of recent developments, especially regarding mobile phase conditions and choice of metal ions. Further, parameters governing selectivity are emphasized. The paper is divided into two parts: LEC at acidic/neutral pH and at alkaline pH. The general characteristics of each part are outlined and illustrated by appropriate applications, including bioanalysis of carbohydrates in complex mixtures. In particular, the exceptionally strong complexation between carbohydrates and certain metal ions at alkaline pH appears promising for enrichment and clean-up possibilities owing to the high degree of inherent selectivity. Finally, future directions are discussed with regard to the intricate isolation and separation problems associated with glycotechnology. Further advances within this field will depend on the development of analytical methodologies for minute amounts (femtomoles) of complex carbohydrate mixtures present on proteins, receptors and cell surfaces and inside the cells.     

Use of 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide and graphene oxide for separation and preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ) ions in different samples

A simple and selective method using a column packed with graphene oxide(GO) as a solid phase extractant has been developed for the multi-element preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ)ions prior to flame atomic absorption spectrometric determinations.The method is based on the sorption of mentioned ions on synthesized GO using 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide as a chelating agent.Several parameters on the extraction and complex formation were optimized.Under the optimized conditions(pH 6,flow rate 9 mL/min),metal ions were retained on the column,then quantitatively eluted by HNO3solution(5 mL,3.0 mol/L).The preconcentration factor was calculated as250.The detection limits for the analyte ions of interest were found in the range of 0.11 ng/mL(Ni2+) to0.63 ng/mL(Cu2+).The column packed with GO was adequate for metal ions separation in matrixes containing alkali,alkaline earth,transition and heavy metal ions.     

Determination of metal ions by on-line complexation and ion-pair chromatography

An ion-pair chromatographic method utilizing on-line complexation and ion-pair formation in a post-column reactor was developed for the determination of copper, palladium, cobalt and iron in mixtures. The system features a reversed-phase column and a second eluent line feeding the ligand reagent, connected after the column via a T-piece, to a mixer and through that to a knitted tubing reactor. The ion-pair former was added to the eluent before the column and the ligand after it. The separation was studied using a binary eluent system containing cetyltrimethylammonium bromide (CTMABr) or tetradecyltrimethylammonium bromide (TDTMABr) in water-methanol (99:1, v/v) as ion-pair former and methanol. In addition, water-methanol (99:1, v/v) containing 1-nitroso-2-naphthol-6-sulphonate (126NNS) as ligand was added to the eluent, through the T-piece, after the column. Mixing of the two eluents took place in the mixer. Methanol was used both isocratically and in gradient addition. Selective UV-VIS detection of the metal-126NNS ion pairs was at wavelengths 230, 260, 310 and 400 nm and their identification was effected in wavelength range 190–600 nm. The metal complex formation in the aqueous methanol eluent evidently governed the retention of the ion pairs, while the selectivity of the method was provided by the different rates of reaction of the metal, the ligand and the ion-pair former in the mixer-reactor system. The detector response for copper, palladium, cobalt and iron was linear up to concentrations of 10 μM. In spiked water-methanol samples the detection limits for these metals ranged from 1·10⁻³ to 1 mg/l. When the on-line complexation and ion-pair formation method was tested with nickel, mercury and zinc, the results proved that these ion pairs were unstable. Because of the insufficient reproducibility of the absorption intensities of these metal ion pairs, their qualitative study could be performed only in the pH range 7–8. The method was successfully applied to real samples after removal of the organic material.     

Selective metal sorption on cross-linked poly(vinylpyridine) resins

The sorption behaviour of several metal ions on five kinds of poly(4- or 2-vinylpyridine) resins, cross-linked with divinylbenzene, and with different surface properties, are examined. All the resins proposed sorb some metal ions effectively in a similar manner by anion-exchange, while the sorption of metal ions by complex formation with the pyridine moiety is strongly affected by the surface properties of the resins. A macroreticular poly(4-vinylpyridine) resin shows high affinity for copper and nickel ions in acetate buffer. Sodium chloride and/or methanol added to the working solutions influence the sorption capacities for metal ions. This resin was applied to the separation of copper/cobalt and nickel/cobalt and the concentration of copper from sea-water by a column operation.     

The Binding of Cu(II) and Zn(II) Ions by Heparin

Abstract

A method is described for measuring the ion binding capacity of heparin. The method is based on the separation of the zinc or copper complex of heparin by gel permeation. It was found that the number of the cation per average molecule of heparin depends on the pH and on the initial concentration of metal cation in solution. The absorption spectrum of heparin-Cu complex is described. The molar absorptivity of this complex is determined, as is the complex formation constant.     

手性配位体交换流动相添加剂法拆分对映体

综述了手性配合基交换色谱法通常采用三种手性相系统中的流动相添加剂方法。主要内容有：（Ａ）手性配合基交换机制,给出了描述对映体对在色谱系统中的保留时间和分离选择性的公式,包括手性选择剂在固定相和流动相中的各种不同情况。公式表明整个色谱往系统的对映体选择性不同于溶液中所存在的选择剂与被选择物作用的情况;（Ｂ）影响配合交换的参数,讨论了金属离子、金属离子／配位体比率、金属离子络合物浓度、固定相、流动相ｐＨ、洗脱顺序、有机调节剂、离子对试剂、流动相离子强度、温度、立体选择性和手性交互识别;（Ｃ）应用。     

Highly sensitive colour change system within slight differences in metal ion concentrations based on homo-binuclear complex formation equilibrium for visual threshold detection of trace metal ions

A new technique of expressing slight differences in metal ion concentrations by clear difference in colour was established for visual threshold detection of trace metal ions. The proposed method is based on rapid change of the mole fraction of the homo-binuclear complex (M₂L) about a ligand in a narrow range of the total metal ion concentration (M_T) in a small excess, in case the second metal ion is bound to the reagent molecule which can bind two metal ions. Theoretical simulations showed that the highly sensitive colour change within slight differences in metal ion concentrations would be realized under the following conditions: (i) both of the stepwise formation constants of complex species are sufficiently large; (ii) the stepwise formation constant of the 1:1 complex (ML) is larger than that of M₂L; and (iii) the absorption spectrum of M₂L is far apart from the other species in the visible region. Furthermore, the boundary of the colour region in M_T would be readily controlled by the total ligand concentration (L_T). Based on this theory, the proposed model was verified with the 3,3′-bis[bis(carboxymethyl)amino]methyl derivatives of sulphonephthalein dyes such as xylenol orange (XO), methylthymol blue (MTB), and methylxylenol blue (MXB), which can bind two metal ions at both ends of a π-electron conjugated system. The above-mentioned model was proved with the iron(III)-XO system at pH 2. In addition, MTB and MXB were suitable reagents for the visual threshold detection of trivalent metal ions such as iron(III), aluminium(III), gallium(III) and indium(III) ion in slightly acidic media. The proposed method has been applied successfully as a screening test for aluminium(III) ion in river water sampled at the downstream area of an old mine.     

Solid-phase extraction and subsequent capillary zone electrophoresis of trace metal ions as soluble dithiocarbamate complexes

Summary Modest detectability in capillary electrophoresis is often a challenge for the determination of trace-level metal ions. This limitation has been addressed by the development of an enrichment procedure combining the formation of metal bis(carboxymethyl)dithiocarbamate complexes, water soluble at basic pH and sparingly soluble in an acidic environment, and solidphase extraction. Appropriate conditions were developed for a solid-phase extraction step well compatible with subsequent capillary electrophoretic separation in terms of the composition of electrophoresis and eluting buffers. At pH below 4 when the ligand carboxyl groups are non-ionized, metal ion complexes have no apparent charge and are efficiently retained on a conventional C₁₆ cartridge. Application of a basic eluent, a borate buffer at pH9, causes the complexes to be ionized and eluted rapidly and quantitatively. Parameters affecting the retention/recovery behavior, such as the pH and ligand concentration of the loading solution, flow-rate, eluting buffer pH and concentration, etc, were examined to attain the best possible enrichment factors for trace metal ions. As a result, an increase in sensitivity over two orders of magnitude was gained that permitted lowering the detection limits for copper(II), lead(II), cadmium(II), nickel(II), and mercury(II) down to a low-μg L⁻¹ level.     

稀土离子及其配合物对二棕榈酰磷脂酰乙醇胺相变性质的影响

用差示扫描量热研究了金属离子和稀土配合物对二棕榈酰磷脂酰乙醇胺(DPPE)脂双层由凝胶态向液晶态相转变的影响T~m的影响。发现加入金属离子提高了DPPE脂双层的相转变温度。其中, Na^+＜Ca^2^+＜Ln^3^+。Pr^3^+的影响较La^3^+强。在pH 7.4时, 柠檬酸镧对T~m影响很小, 相反在pH 2.0时, 则降低相变温度T~m。乳酸稀土在pH 2.0和pH 7.4时都显著提高T~m, 在中性条件下, 对T~m影响更大。同时, 乳酸稀土较相同浓度下的稀土离子影响大, 说明乳酸稀土中稀土离子和乳酸根配体存在协同作用。我们初步探讨了金属离子以及稀土配合物对DPPE脂双层相变温度影响的原因。