Chelation Ion Chromatography Research Articles

Investigation of new chelation ion chromatography procedure to determine the surface composition of powdered metal oxide samples in the solid state

Numerous tests have been conducted on the feasibility of characterizing the surfaces of metal oxide powders using HPLC. An in-line filter housing was modified to serve as a sample chamber to replace the sample loop. A gradient pump was used to gradually increase eluent acidity to find the conditions at which the surface of a metal oxide powder began to dissolve. The theoretical masses of surface monolayers of metal oxide powders were compared with the experimentally determined masses of dissolved material thought to be from the surface to test whether surface and bulk dissolution phenomena in acidic conditions are separable and quantifiable. A set of methods was tested that could first dissolve a metal oxide sample’s surface, then separate and detect analyte species by chelation ion chromatography. Surface characterization by ion chromatography could be more cost-effective than existing methods, and reveal chemical properties of the sample where existing methods only give physical composition and properties.

Retention of Cr(III) by high-performance chelation ion chromatography interfaced to inductively-coupled plasma mass spectrometric detection with collision cell

High-performance chelation ion chromatography (HPCIC) was employed to retain cationic Cr(III) on an anion-exchange column and hence allow the separation of the two most prevalent forms of chromium, Cr(III) and Cr(VI). A mobile phase of nitric acid was utilized at pH = 1.5; additionally, 2,6-pyridinedicarboxylic acid was used at a concentration of 6 mM. Additives with different structural characteristics were used in an effort to elucidate retention mechanisms. Inductively-coupled plasma mass spectrometry was used for chromium detection. A collision cell was utilized to reduce chloride-based polyatomic ions that may interfere with the detection of Cr(III), and a detection limit study yielded levels in the low part-per-billion range. The newly developed method was applied to the chromatographic analysis of samples of an incubation medium containing Cr(VI) incubated with cell nuclei.

Non-trivial temperature effects on the cation exchange chromatography and chelation ion chromatography of metal ions.

The effect of column temperature upon the retention of metal ions on sulfonated and mono-, di-, and amino-carboxylated cation exchange columns has been investigated. The retention of alkali, alkaline earth and transition metal ions on each of the above types of cation exchanger was studied over the temperature range 19-65 degrees C. A major difference between the behaviour of mono- and divalent metal ions was shown on each of the above stationary phases, with the monovalent alkali metals exhibiting clearly exothermic behaviour (a decrease in retention with increased temperature) under acidic eluent conditions and an apparent relationship between retention factor and the magnitude of the temperature effect. The effect of temperature upon alkaline earth metal ions was less defined, although strongly endothermic behaviour (increase in retention with temperature) could be seen on all stationary phases through correct choice of eluent. The transition metal ions studied showed endothermic behaviour on all four stationary phases, with the sulfonated column unexpectedly showing the largest increases in retention. The above behaviour can be partially explained through the dominance of the type of solute-stationary phase interaction governing retention. In several of the above columns, both ion-exchange and surface complexation interactions can occur, with the effects of temperature indicating which process dominates under specific eluent conditions.

Fabrication of an Aurin Tricarboxylic Acid Immobilized Chelating Polymer for the Ion Chromatographic Determination of Trace Metal Ions in Highly Mineralized Waters

A high efficiency 7 µm neutral polystyrene divinylbenzene resin, impregnated with the chelating dye aurin tricarboxylic acid (ATA), was investigated for the separation and quantitative determination of Cd(II), Pb(II) and Cu(II) in high ionic strength matrices including mineral waters, by chelation ion chromatography. The fabricated ATA substrate demonstrated a unique selectivity pattern for transition and heavy metal ions, being more selective towards the environmental pollutants Cd(II) and Pb(II) in particular, in comparison with dyes containing iminodiacetate groups which have been extensively investigated recently. A development of the dye impregnation procedure, using ultrasound, siginificantly increased the capacity of the chelating column by a factor of four. Utilising a developed pH gradient elution, in an eluent of 0.1 M potassium nitrate to suppress ion exchange interactions, allowed Cd(II), Pb(II) and Cu(II) to be baseline resolved from other transition metals and the alkaline earths within 30 min. Detection limits were considerably improved by buffering the 4-(2-pyridylazo)resorcinol post column reagent with borate instead of ammonia, resulting in a threefold increase in sensitivity for Cd(II) and near twofold for Pb(II) at 520 nm. The developed procedure was applied to the determination of these metals in highly mineralised water and high ionic strength matrices. The calibration curves produced good linearity (>0.994), with excellent detection limits of 1 µg L−1 for Cd(II) and 5 µg L−1 for both Pb(II) and Cu(II), respect vely.

Determination of vanadium, molybdenum and tungsten in complex matrix samples by chelation ion chromatography and on-line detection with inductively coupled plasma mass spectrometry

In this work, two kinds of chelating resin, bis(2-aminoethylthio)methylated resin (BAETM) and γ-aminobutyrohydroxamate resin (γ-ABHX) were synthesized. Of these, the former has a hydrophobic skeleton, and the latter a hydrophilic skeleton. The functionalities of each were 0.91 and 2.21 mmol g −1, respectively. The chelating behavior of these resins towards vanadium, molybdenum and tungsten as a function of pH was studied. To perform trace metals analysis in complex matrices, a hyphenated method-chelation ion chromatography (CIC) coupled on-line detection with inductively coupled plasma mass spectrometry (ICP-MS) was developed. With a BAETM resin column (5×0.4 cm i.d.) as the separator, a sample volume of 20 μl, nitric acid (pH 1.5) as the eluent and a flow rate of 1 ml min −1, the detection limits for the determination of vanadium, molybdenum and tungsten were lower than 0.05 ng ml −1and the linear ranges were up to 100 ng ml −1 for each element. By increasing the injected sample volume to 250 μl, the resin concentrator improved the detection limit to 0.01 ng ml −1. For the determination of these elements (5 ng ml −1 for each) spiked in artificial sea water samples, γ-ABHX resin column (3×0.6 cm i.d.) demonstrated well resolved peak separation between the analytes and the matrix elements—calcium and magnesium, by using sodium nitrate (10 ml, 10 −4 M) as the eliminator.

Measurement and Effect of Trace Element Contaminants in Alum

Analytical methods were developed to accurately determine the levels of the most prevalent trace metal contaminants in a variety of alum feedstocks used in the coagulation process of drinking water treatment. A combination of chelation ion chromatography, chelation extraction–atomic absorption spectrometry, and hydride generation atomic fluorescence allowed for the selective isolation of trace metals from the alum matrix with a high degree of precision and sensitivity. Trace levels of arsenic, cadmium, chromium, copper, manganese, nickel, lead, and zinc were found in the range of 20–330 μg/g aluminum (Al); iron, recognized as a co‐contaminant in the raw material, was present at 20 mg/g Al. By extrapolating these measured levels to an upper yet realistic applied dosage of alum in drinking water treatment, the authors could predict the contaminants' concentrations (under a worst‐case scenario) in both the finished water and alum sludge. For finished water even if it was assumed that none of the trace metals was removed during coagulation, the contaminants' concentrations did not exceed drinking water standards, and their contribution reached only a small fraction of the permitted maximum contaminant level. In a scenario in which the trace metals were assumed to be removed during the coagulation process, levels that would accumulate in the alum sludge would not be significant enough to heavily influence decisions to apply alum sludge to land for agricultural uses.

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 KNO 3 (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 μg/l in a freshwater certified reference material (NIST 1640).

High-Performance Chelation Chromatography of Metal Ions on Sorbents with Grafted Iminodiacetic Acid

The chromatographic behavior of some alkaline-earth, transition, heavy, and rare-earth metals on a number of complexing sorbents containing surface iminodiacetic acid (IDA) functional groups is studied. The conditions under which metal retention is determined by complexation on the sorbent surface were established, and the main principles of a new variant of the liquid chromatography, i.e., high-performance chelation ion chromatography (HPCIC), are formulated. The efficiency and selectivity of separation of the metal ions are considered depending on the type of the IDA bonding, the sorbent matrix parameters, the eluent composition, and the temeprature of the chromatographic column. Under optimal conditions, the metal retention is shown to linearly correlate with the stability constants of the respective complexes in the double-logarithmic scale. The application of HPCIC to the analysis of multicomponent systems is considered.

Determination of actinides in environmental and biological samples using high-performance chelation ion chromatography coupled to sector-field inductively coupled plasma mass spectrometry

High-performance chelation ion chromatography, using a neutral polystyrene substrate dynamically loaded with 0.1 m M dipicolinic acid, coupled with sector-field inductively coupled plasma mass spectrometry has been successfully used for the separation of the actinides thorium, uranium, americium, neptunium and plutonium. Using this column it was possible to separate the various actinides from each other and from a complex sample matrix. In particular, it was possible to separate plutonium and uranium to facilitate the detection of the former free of spectral interference. The column also exhibited some selectivity for different oxidation states of Np, Pu and U. Two oxidation states each for plutonium and neptunium were found, tentatively identified as Np(V) and Pu(III) eluting at the solvent front, and Np(IV) and Pu(IV) eluting much later. Detection limits were 12, 8, and 4 fg for 237Np, 239Pu, and 241Am, respectively, for a 0.5 ml injection. The system was successfully used for the determination of 239Pu in NIST 4251 Human Lung and 4353 Rocky Flats Soil, with results of 570±29 and 2939±226 fg g −1, respectively, compared with a certified range of 227–951 fg g −1 for the former and a value of 3307± 248 fg g −1 for the latter.

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 KNO 3 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 KNO 3 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.

Determination of uranium in environmental matrices by chelation ion chromatography using a high performance substrate dynamically modified with 2,6-pyridinedicarboxylic acid

Determination of uranium in environmental matrices by chelation ion chromatography using a high performance substrate dynamically modified with 2,6-pyridinedicarboxylic acid

SIMULTANEOUS DETERMINATION OF HEAVY AND TRANSITION METALS IN BIOLOGICAL SAMPLES BY CHELATION ION CHROMATOGRAPHY

A highly sensitive method of simultaneous separation and determination of Pb2+, Cu2+, Cd2+, Co2+, and Ni2+ was developed and evaluated by on-line sample pretreatment of chelation ion chromatography. Bulk quantities of anions, alkali metals, alkaline earth metals, tervalence cations, and other interfering components were eliminated by pyrophosphoric acid / ammonium acetate buffer solution (pH 5.5), while retaining heavy and transition metals on iminodiacetate-based resins. Then, they were disabsorbed and transferred to sulfonated cation exchangers. Finally, the concentrated trace metals were separated on a bifunctional ion exchange column by a concentration gradient of oxalic acid and sodium nitrate eluents, coupled with post-column sepectrophotometric detection with 2-[(5-bromo-2-pyridyl)-azo]-5-diethyl-aminophenol (5-Br-PADAP) at 560 nm. The method detection limits (signal-to-noise 3:1) were at or below μg L−1 levels. This technique was validated by analyzing standard biological references.

Determination of uranium in environmental matrices by chelation ion chromatography using a high performance substrate dynamically modified with 2,6-pyridinedicarboxylic acid

Chelation ion chromatography, involving a high efficiency neutral polystyrene-divinylbenzene resin dynamically coated with 2,6-pyridinedicarboxylic acid, has been developed as a novel technique for the quantitative determination of uranium in complex matrices. An isocratic separation method, using an eluent consisting of 1M KNO3, 0.5M HNO3 and 0.1 mM 2,6-pyridinedicarboxylic acid, allowed the uranyl ion to elute away from matrix interferences in under ten minutes. Detection was achieved using an Arsenazo III post column reaction system. Good recoveries were obtained from spiked mineral water and sea water and the standard addition curves produced good linearity (r2>0.997) with a detection limit, calculated as twice baseline noise, of 20 μg L−1. The procedure was applied to the determination of trace uranium in standard reference water and sediment samples. The results obtained compared well with the certified values for uranium.

Improved scheme of chelation ion chromatography with a mixed eluent for the simultaneous analysis of transition metals at μg 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/Na 2C 2O 4/LiOH/NaCl) for the analysis of seven metals (Pb 2+, Cu 2+, Ni 2+, Zn 2+, Co 2+, Cd 2+ and Mn 2+) at μg 1 −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 μg l −1 when 4 ml of sample is pre-concentrated. The results of real sample analysis are satisfactory.

Determination of beryllium in a stream sediment by high-performance chelation ion chromatography

High-performance chelation ion chromatography (HPCIC), involving a chelating silica substrate bonded with aminomethylphosphonic acid, has been developed as a novel technique for the quantitative determination of beryllium in complex matrices. An isocratic separation method, using an eluent containing 1 M KNO 3, 0.5 M HNO 3 and 0.08 M ascorbic acid, allowed the Be 2+ to elute away from the sample matrix peak in under 6 min in a sample containing in excess of 800 mg l −1 matrix metals. A detection limit of 35 μg l −1 Be(II) was found using a post-column reaction involving Chrome Azurol S (CAS), 1 M hexamine and 10 m M EDTA buffered at pH 6. The standard addition curve gave excellent linearity ( R 2>0.999). The procedure was applied to the determination of trace beryllium in a certified sediment sample. The results obtained compared well with the certified value for beryllium.

Chelation ion chromatography of metal ions using high performance substrates dynamically modified with heterocyclic carboxylic acids

This study shows that stable high efficiency metal chelating substrates can be formed from neutral stationary phases by dynamically loading with low molecular weight complexing agents present in the mobile phase. Three complexing pyridine carboxylic acids, namely, picolinic, dipicolinic and quinaldic acids were used to dynamically coat both a C 18silica gel and a polystyrene resin and the separation performance compared for groups of metal ions. Quinaldic acid gave the largest selectivity coefficients as it produced the most concentrated coating, while picolinic acid was too weakly adsorbed to give any significant metal retention apart from copper. Dipicolinic acid was found to be especially selective for uranium(VI). In general, retention order was the same on both stationary phases, but the polystyrene resin produced the most efficient separations. Interesting selectivity differences were found between the different acid coatings. For example, for dipositive ions, the retention order using a dipicolinic acid coating was Mn(II) < Cu(II) < Ni(II) < Zn(II) < Pb(II) < Cd(II), whereas using quinaldic acid it was Mn(II) < Pb(II) < Cd(II) < Zn(II) < Ni(II) < Cu(II).

Aminophosphonate-Functionalized Silica: A Versatile Chromatographic Stationary Phase for High-Performance Chelation Ion Chromatography

The chromatographic behavior of alkaline earth metals, Cu(II), Mn(II), Co(II), Zn(II), Ni(II), Pb(II), and Cd(II) on a chelating aminomethylphosphonic acid-functionalized silica column was studied in eluants with high ionic strength to suppress ion exchange. Unusual variations were found in plots of capacity factor against pH demonstrating changes in retention order, suggesting a change in the coordination of metal ions from O,O to N,O,O chelation. Increased affinity of the chelating ion exchanger to heavy metals and in particular Mn(II) was observed at low pH. Examples are shown of high-efficiency separations of groups of metal species with varying retention orders at different pH values, including a separation of eight metal species in under 16 min. These characteristics make aminophosphonate chelating substrates a useful and more versatile phase for high-performance chelation ion chromatography than iminodiacetate phases.

High-performance chelation ion chromatography of transition and heavy metal ions on polystyrene–divinylbenzene resin dynamically modified with 4-chlorodipicolinic acid

A neutral polystyrene–divinylbenzene column, combined with 4-chlorodipicolinic acid present in the mobile phase, has been developed as a chromatographic system for the high efficiency isocratic separation of transition and heavy metal ions. Retention arises from the formation of a stable dynamically coated chelating stationary phase, the capacity of which is dependent upon both the pH and ligand concentration in the eluent. The results obtained illustrate the increased loading and selectivity of this chlorinated chelating molecule in comparison with unsubstituted dipicolinic acid, exemplified by the separation of 7 metals in under 8 min. The column also displayed a strong affinity for CdII and an unusual retention for NiII, which showed a good symmetrical peak shape.

Chelation ion chromatography of metal ions using an ODS reversed-phase column and a mobile phase containing methylthymol blue

An ODS reversed-phase column has been used in conjunction with an aqueous mobile phase containing methylthymol blue for the separation and visible detection of metal ions. Retention is due to the formation of a dynamically coated chelating stationary phase and is dependent upon mobile phase pH and ligand concentration. Post-column addition of a buffer solution enables the sensitive visible detection of the metal ions as methylthymol blue complexes at 600 nm. The developed method resulted in improved peak efficiencies and a differing selectivity for certain metal ions, when compared to a pre-coated methylthymol blue chelating column (where the ligand was first used to modify the stationary phase, but was not included as a component of the mobile phase). The isocratic separation and visible detection of 12 metal ions was possible, including a number of the lanthanide series metals.

γ-Aminobutyrohydroxamate resins as stationary phases of chelation ion chromatography

γ-Aminobutyrohydroxamate resin and its derivatives were prepared and employed as stationary phases in chelation ion chromatography for the simultaneous determination of trace metal ions in sea water and biological sample. The method consists of preconcentration of a 25 ml sea water or biological sample on a γ-aminobutyrohydroxamate resin column; alkali and alkaline earth metal ions are removed from the resin with potassium nitrate (0.01 M) solution, the metal ions are eluted with oxalic acid (0.03 M, pH 2.6) and separated on a Dionex CS-5 column , followed by postcolumn derivatization with 4(2-pyridylazo)resorcinol and spectrophotometric detection at 495 nm. The concentration and separation steps are automated. The method shows good linearity for Co(II), Cu(II), Mn(II), Ni(II) and Zn(II) ranging from 0.5 to 10 ng ml −1 and that for Cd(II) ranging from 2 to 40 ng ml −1. The detection limits for Co(II), Cd(II), Cu(II), Mn(II), Ni(II) and Zn(II) are 0.4, 1.2, 0.5, 0.4, 0.8 and 0.3 ng ml −1, respectively. The analytical reliability of the proposed method was evaluated by analyzing oyster tissue standard reference material (NIST, SRM 1566a).