Ion chromatography of transition metals on an iminodiacetic acid bonded stationary phase

Electrokinetic and adsorption properties of sepiolite modified by 3-aminopropyltriethoxysilane

Surface modification of clay minerals has become increasingly important for improving the practical applications of clays such as fillers and adsorbents. An investigation was carried out on the surface modification of sepiolite with aminopropylsilyl groups in 3-aminopropyltriethoxysilane (3-APT). The zeta potential of the modified sepiolite suspensions was measured as a function of initial electrolyte concentration and equilibrium pH using a Zeta Meter 3.0 for modified sepiolite. The utility of the 3-APT-modified sepiolite was investigated as an adsorbent for removal of various heavy metal ions such as Fe, Mn, Co, Zn, Cu, Cd and Ni from aqueous solutions. The effects of various factors on the adsorption, such as pH, ionic strength and temperature of the solution were studied. The results showed that the amount adsorbed increases with solution pH in the pH range of 1.5 and 7.0; indicated that the modified sepiolite adsorbed Fe and Mn ions more than other metal ions such as Co, Zn, Cu, Cd and Ni. It was found that the temperature had an important effect on metal ion adsorption by the modified sepiolite. The adsorption isotherm has been determined and data have been analyzed according to the Langmuir and Freundlich models.

Recent developments in the high-performance chelation ion chromatography of trace metals

There have been a number of significant developments in the high-performance chelation ion chromatography (HPCIC) of trace metals in recent years. This review focuses on these developments, while giving important information on the fundamental parameters controlling the chelation sorption mechanism, including type of chelating group, stability constants, kinetics, and column temperature. The discussion pays particular attention to the types and properties of efficient chelating stationary phases which have been fabricated for certain groups of metals. The review also describes a number of major improvements in postcolumn reaction detection including the use of the latest reagents and noise reduction strategies to improve sensitivity and reduce LOD. In the final section, an indication of the applicability of HPCIC to a range of complex sample types is given with some key examples and chromatograms using the latest high-efficiency chelating phases.

Novel ion chromatographic stationary phases for the analysis of complex matrices

Ion chromatography (IC) has a proven track record in the determination of inorganic and organic anions and cations in complex matrices. Recently, application of IC to the separation and determination of bio-molecules such as amino acids, carbohydrates, nucleotides, proteins and peptides has also received much attention. The key to the determination of all of the above species in the most analytically challenging complex matrices is the ability to manipulate selectivity through control of stationary phase chemistry, mobile phase chemistry and the choice of detection method. This Tutorial Review summarises some of the most significant recent advances made in IC stationary phase technology. In particular, the review details stationary phases specifically designed for ion analysis in complex sample matrices, and considers in which direction future stationary phase development might proceed.

Ion exchange properties of monolithic and particle type iminodiacetic acid modified silica

A 10 cm silica monolith has been modified with iminodiacetic acid (IDA) groups and characterised for its selectivity toward alkali, alkaline earth, and selected transition metal cations. Physical characterisation of the modified monolith found non-homogeneous modification along the length of the monolith, although sufficient capacity was achieved to facilitate significant retention of alkaline earth and transition/heavy metal ions over a range of eluent pH and ionic strength conditions. For alkaline earth and transition/heavy metal ions, selectivity of the 10 cm IDA monolith closely matched that seen with a 25 cm IDA modified silica gel particle packed column, although the separation of alkali metal ions was noticeably poorer on the monolithic column. Peak efficiencies for most metal ions were of a similar order for both column types, except for Zn(II), which showed significant peak broadening on the IDA monolithic column.

The determination of trace metal pollutants in environmental matrices using ion chromatography

A review is presented detailing the development of ion chromatography (IC) as a selective analytical tool for the determination of toxic metals and their organic species in many environmental sample matrices. A brief outline of ion chromatographic principles, together with an overview of the stationary phases used to separate metals, namely ion exchangers, modified ion pair sorbents and chelating ion exchangers, and the methods for detecting metal ions including hyphenation with spectroscopy and sample preparation schemes are also given, prior to a critical examination of developed methods for various metals including arsenic, chromium, cadmium, lead, mercury, beryllium, aluminium and uranium since 1990.

Enzyme-based molecular imprinting with metals

Aromatic monomers with various functional groups were utilized in horseradish peroxidase-catalyzed polymerization reactions with metal ions Cu(II), Ni(II), and Fe(III) as imprinting templates. The approach described combines molecular imprinting with enzymatic free radical coupling. Selectivity in metal ion affinity between the various polymer products was assessed and found to depend on the metal used in the imprinting process using aniline, tyramine, and phenol as monomers. Selectivity in binding metals was found when polymers imprinted with copper, nickel, or iron were screened against the three metals, with preference for the metal used in the imprinting step. A model for the structural features of the putative imprinted polymers is proposed based on electron paramagnetic resonance, NMR, and IR analysis. Specific potential benefits to this imprinting method include reactivity with a wide range of aromatic monomers to provide more diverse options for molecular recognition with the target analyte and thus polymer products with higher selectivity, mild reaction conditions for the enzyme polymerization step to enable imprinting against labile substrates, imprinted polymeric products that contain conjugated backbones that could be suitable for electronics-based biosensor applications, and a potential for combinatorial selection to further enhance specificity.

On-column complexation of metal ions using 2,6-pyridinedicarboxylic acid and separation of their anionic complexes by capillary electrophoresis with direct UV detection

On-column complexation of metal ions with 2,6-pyridinedicarboxylate (2,6-PDC) to form anionic complexes enabled their separation by capillary zone electrophoresis with direct UV detection at 214 nm. Nine metal ions, Cu2+, Zn2+, Ni2+, Cd2+ Mn2+, Pb2+, Fe3+, Al3+ and Ca2+, were determined in less than 7 min using 10 mM 2.6-PDC solution containing 0.75 mM tetradecyltrimethylammonium bromide at pH 4.0. Satisfactory working ranges (20-300 microM), detection limits (3-10 microM) and good repeatability of the peak areas (RSD 2.1-4.2%, n=5) were obtained using hydrodynamic injection (30 s). The proposed method was used successfully for the determination of Mn2+, Fe3+, Al3+ and Ca2+ in groundwaters.

Ionic strength, pH and temperature effects upon selectivity for transition and heavy metal ions when using chelation ion chromatography with an iminodiacetic acid bonded silica gel column and simple inorganic eluents

An investigation into the selectivity of an iminodiacetic acid (IDA) modified silica gel column for transition and heavy metal ions using non-chelating inorganic eluents has been carried out. A number of eluent parameters were investigated to determine the exact retention mechanism taking place and to control selectivity. The parameters studied were eluent ionic strength and the nature of the inorganic salt used, eluent pH and eluent temperature. The results obtained showed how despite certain metal ions exhibiting similar stability constants with the bonded IDA groups, careful control of each of the above parameters, in particular eluent chloride ion concentration and eluent temperature, could result in large changes in selectivity. Optimal conditions for the isocratic and gradient separation of Mg(II), Ca(II), Mn(II), Cd(II), Co(II), Zn(II) and Pb(II) were determined. An isocratic method using a 0.035 M KCl, 0.065 M KNO3 (pH 2.5) eluent was successfully applied to the determination of Mn(II), Cd(II), Co(II) and Zn(II) at concentrations between 20 and 121 microg/l in a freshwater certified reference material (NIST 1640).

Ion chromatography on chelating stationary phases: separation of alkali metals

Analytical 250x4.6 mm I.D. columns packed with iminodiacetic acid (IDA) derivatised silica were used to separate alkali metal ions and the ammonium ion in combination with non-suppressed conductivity detection. The addition of 2.5-10 mmol/l of the macrocyclic crown ether 18-crown-6 to the nitric acid eluent resulted in a change in the elution order and a significant improvement in the resolution between potassium and ammonium because of selective complexation of potassium. However, the admixture of 15-crown-5 did not improve the resolution of lithium and sodium, although 15-crown-5 is a selective complexing agent for sodium. Retention and resolution of lithium, sodium, ammonium, cesium, rubidium and potassium ions increased at lower temperatures down to 1 degree C. The simultaneous separation of alkali and transition metals under isocratic conditions was achieved with an eluent comprising 10 mmol/l 18-crown-6, 1.5 mmol/l dipicolinic acid, and 1.9 mmol/l nitric acid. The chromatographic system enabled the quantitation of alkali metal ions with detection limits in the low ppb range and excellent linearity. Finally, the applicability of the method was approved by quantitation of sodium, ammonium and potassium in different water samples.

Determination of trace alkaline earth metals in brines using chelation ion chromatography with an iminodiacetic acid bonded silica column

The chromatographic behaviour of alkaline earth metals on iminodiacetic acid bonded silica was studied. It was found that the ionic strength of the eluent greatly affected both retention time and selectivity by controlling the extent to which either simple ion exchange or surface complexation was responsible for retention. With a 0.1 M KNO3 eluent, the retention order was Mg(II), Sr(II), Ca(II) and Ba(II), indicating a strong contribution to retention from ion exchange. However, when using a 1.5 M KNO3 eluent, Ba(II) was found to elute first, indicating complexation to be more dominant under these conditions (pH 4.2). The effect of the ionic strength of the sample was also studied and it was found that by matching the eluent cation with that of the sample matrix, efficient separations of alkaline earth metals in 1.0 M NaCl and KCl brines could be obtained without matrix system peaks. Using post-column reaction with o-cresolphthalein complexone, trace levels of Ca(II) and Mg(II) were determined in medicinal NaCl saline solution and laboratory-grade KCl.

Improved scheme of chelation ion chromatography with a mixed eluent for the simultaneous analysis of transition metals at microg l(-1) levels

An improved scheme of chelation ion chromatography (CIC) system and a mixed eluent for the simultaneous determination of transition metals are described. A method based on the improved CIC system and the mixed eluent (PDCA/Na2C2O4/LiOH/NaCl) for the analysis of seven metals (Pb2+, Cu2+, Ni2+, Zn2+, Co2+, Cd2+ and Mn2+) at microg l(-1) levels in a single isocratic elution is developed. The optimize conditions which are different from references for analyte concentration and chromatographic separation are studied in detail. D418 chelation resin is used to further reduce values of the reagent blank. The above seven metals are measured at 565 nm using 2-[(5-Bromo-2-Pyridyl)-Azo]-5-Diethyl-AminoPhenol(5-Br-PADAP) as the post-column derivatizing reagent. Detection limits range from 0.3 to 12 microg l(-1) when 4 ml of sample is pre-concentrated. The results of real sample analysis are satisfactory.

Examination of the protein binding behaviour of immobilised copper (II)-2,6-diaminomethylpyridine and its application in the immobilised metal ion affinity chromatographic separation of several human serum proteins

A new metal ion chelator has been developed for use in the immobilised metal ion affinity chromatography (IMAC) of proteins. The aromatic tridentate ligand 2,6-diaminomethylpyridine (bisampyr), 1, was prepared as the dihydrochloride salt, via a two step synthesis from 2,6-pyridinedimethanol, 2, and immobilised onto Sepharose CL-4B through an epoxide coupling procedure. The resulting sorbent was chelated with Cu2+ ions to a density of 420 micromol Cu2+ ions per g gel and then characterised by frontal analysis using the protein, horse heart myoglobin (HMYO), at pH 7.0 and 9.0. From the resulting adsorption isotherms, the adsorption capacity, qm, for HMYO at pH 7.0 and pH 9.0 with the immobilised Cu2+-bisampyr Sepharose sorbent was found to be 1.27 micromol protein/g gel and 1.43 micromol protein/g gel, whilst the corresponding dissociation constants, K(D)s, were 18.0 x 10(-6) M and 16.0 x 10(-6) M respectively. The results confirm that the HMYO-Cu2+-bisampyr complex had similar stability at these pH values. This finding is in contrast with the situation observed with some other commonly used IMAC chelating ligates such as Cu2+-iminodiacetic acid (Cu2+-IDA) or Cu2+-nitrilotriacetic acid (Cu2+-NTA). Using human serum proteins, the interactive properties of the immobilised Cu2+-bisampyr Sepharose sorbent were further characterised at pH 5.0, 7.0 and 9.0 with specific reference to the binding behaviour of albumin, transferrin, and alpha2-macroglobulin.