Trace analysis of heavy metal ions by ion chromatography

Summary An ion chromatographic separation technique for heavy metal ions is described. Using pressure-stable, silica-based, ion-exchange supports and standard HPLC equipment with post-column reaction detector high resolution is achieved as well as extremely high sensitivity in the parts per trillion (ppt)-range.     

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.     

Zwitterionic ion chromatography using a dynamically coated column and mobile phase recycling

An investigation into the use of zwitterionic ion chromatography for the determination of inorganic anions in water samples was carried out. When using an ODS stationary phase precoated with Zwittergent 3-14 and a pure water mobile phase, the stability of the adsorbed coating was insufficient for quantitative work. Recycling of the water mobile phase was used to stabilise the zwitterionic coating, and resulted in improved retention time precision (15.2% RSD down to 2.4% RSD for nitrate). Post-detection cation- and anion-exchange columns in acid and hydroxide form removed sample ions from the recycling mobile phase, with the desorbed Zwittergent 3-14 passing through unretained and passing back through the pump to the analytical column. A 200-ml volume of mobile phase was recycled over a 3-week period with retention times for sulphate, chloride and nitrate standards injected at the start and end of the period varying less than 2.5%. The same system was then used with a mobile phase containing 2 mM Zwittergent 3-14. This resulted in further improvements in retention time (0.2-0.5% RSD, n = 10) and peak area precision (2.6-6.0% RSD, 1 mM standards) and improved peak efficiencies (2421-4047 N). The developed method was applied to water samples, and results compared to those obtained using anion-exchange chromatography. All sample cations were exchanged to sodium using an off-line cation-exchange procedure prior to injection.     

Uptake of transition metal ions using liposomes containing dicetylphosphate as a ligand.

The uptake of Cu2+ was investigated using various types of liposomes composed of phosphatidylcholine (PC), cholesterol (Chol) and dicethylphosphate (DCP). DCP played a role as a ligand for Cu2+. Multilamellar vesicles (MLVs) were more effective for the uptake of Cu2+ compared to unilamellar vesicles prepared by the extrusion technique. The uptake efficiency of MLVs for Cu2+ was dependent on the molar ratio of DCP in MLVs. The uptake percent of Cu2+ was 92% using MLVs having a PC:DCP:Chol molar ratio of 4:3:3; 95% of the total vesicle Cu2+ was bound to DCP of the outer membrane surface of the MLVs, and the remaining 5% of the total Cu2+ was distributed into the interior side of the MLVs. MLVs having a PC:DCP:Chol molar ratio of 4:3:3 were also effective as separation media for Mn2+, Co2+, Ni2+ and Zn2+. The uptake efficiency of the MLVs for the transition-metal ions increased in the order Co2+ < Zn2+ < Ni2+ < Mn2+ < Cu2+.     

Determination of aluminium using high performance chelation ion chromatography

The suitability of high performance chelation ion chromatography (HPCIC) using postcolumn reaction for the separation and determination of dissolved aluminium in complex samples was investigated. Use of a chelating ion-exchanger allowed for differentiation between kinetically labile and kinetically stable species of aluminium. Separation through a combination of chelation and cation-exchange was achieved using a 200 x 4.0 mm id column packed with particles of silica functionalised with iminodiacetic acid, with nitric acid-potassium chloride eluents. A temperature anomaly causing a five-fold increase in column efficiency for aluminium is believed to be a result of localised temperature effects in the particular type of instrument used. Postcolumn reagents investigated for the photometric detection included Tiron, Pyrocatechol Violet, Chrome Azurol S, and Eriochrome Cyanine R. The lowest detection limit (2.7 microg/L for a 100 microL sample volume) was achieved using 0.25 mM Eriochrome Cyanine R in 0.2 M hexamine (pH 6.1) with 1 mM cetyltrimethylpyridium bromide (CTAB). The optimised HPCIC system was applied successfully to the quantification of labile aluminium in paper mill process water.     

Complexes of the selected transition metal ions with 4-methoxycinnamic acid

In this study, 4-methoxycinnamates of Mn(II), Co(II), Ni(II), Cu(II), Cd(II), Nd(III) and Gd(III) were synthesised. From the infrared (IR) spectra analysis of complexes, sodium salt and according to the spectroscopic criteria the carboxylate groups seem to be bidentate chelating. The complexes of 4-methoxycinnamates lose the water molecules in one or two steps. The final products of their decomposition are oxides of the respective metals. The enthalpy values of dehydration process were determined. The FTIR spectra of the gas phase products indicate that the decomposition of the complexes is connected mainly with the release of molecules of water (H₂O), carbon dioxide (CO₂), carbon monoxide (CO), methane (CH₄) and other hydrocarbons. The analysed compounds follow the Curie?CWeiss law. The magnetic moment values experimentally determined change as follows: from 5.90??? _B to 6.27??? _B for Mn(II) complex, from 4.57??? _B to 4.99??? _B for Co(II) complex, from 3.68??? _B to 3.30??? _B for Ni(II) complex, from 1.87 ?? _B to 1.96 ?? _B for Cu(II) complex, from 3.06??? _B to 3.51??? _B for Nd(III) complex, and from 6.91??? _B to 6.90??? _B for Gd(III) complex.     

Paper chromatography of metal ions in solvents containing methylamine

Summary The effect of methylamine and methylamine hydrochloride has been systematically investigated in the paper chromatography of various metal ions. It has been found that methylamine hydrochloride like EDTA helps in preventing tailing. A new separation of Fe, Mn, Ni, and Co has been developed. The R_f-values are 0.97, 0.49, 0.08, 0.79 respectively and the solvent system used is ethylacetoacetate/methylamine hydrochloride/conc. hydrochloric acid (2027). The values are equally spaced, the spots are compact and the separation is probably the best yet recorded.

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Zusammenfassung Es wird über eine systematische Untersuchung des Einflusses von Methylamin und Methylaminhydrochlorid bei der Papierchromatographie verschiedener Metallionen berichtet. Dabei ergab sich, da\ Methylaminhydrochlorid Ähnlich wie ÄDTA zur Verhinderung der Schwanzbildung benutzt werden kann. Zur Trennung von Fe, Mn, Ni und Co wird ein Lösungsmittel aus Acetessigester, Methylaminhydrochlorid und konz. SalzsÄure (2027) empfohlen (R_f-Werte: 0,97, 0,49, 0,08 bzw. 0,79), mit dem sehr gute Ergebnisse erzielt wurden.

     

High-performance liquid chromatography of metal ions on a bonded stationary phase

Summary High performance liquid chromatography was used to separate Cu²⁺, Ni²⁺, and Zn²⁺ ions. A column packed with a -diketone bonded phase on silica gel and a mobile phase composed of trifluoroacetylacetone in acetone was used for the separation. After post-column reaction with a color-forming reagent, the metals were detected by absorption in the visible region.Currently assigned to 1155th Technical Operations Squadron, McClellan Air Force Base, California, 95652, USA     

Selective separation of some ecotoxic transition metal ions from aqueous solutions using immobilized macrocyclic material containing solid phase extraction system

A simple flow-based method was developed for the simultaneous separation of certain transition metal ions (Co, Ni, Cu, Zn, Cd) from aqueous systems, which ions show ecotoxic effects when present at elevated concentrations. A silica-gel-bonded macrocycle system, commonly known as molecular recognition technology (MRT) gel, was used for solid phase extraction (SPE) of the target analytes. The collection behavior of the MRT-SPE system was studied based on pH. Fortified deionized water samples containing 250 μg L⁻¹ of each of the elements were treated at the flow rate of 1 mL min⁻¹. The collected analytes were then eluted by 3 M HNO₃ and analyzed using inductively coupled plasma spectrometry. Detection limits of the proposed technique were in the range of 0.004–0.040 μg L⁻¹ for the studied metal ions. The validity of this separation technique was checked with spiked ‘real’ water samples, which produced satisfactory recoveries of 96–102%. The non-destructive nature and highly selective ion-extraction capability of the SPE material are the most important aspects of the proposed method and they are the main focus of this paper.      

Behaviour of plasmalogens during high-performance liquid chromatography on a silica column with a mobile phase containing phosphoric acid

Silica high-performance liquid chromatographic separation of phospho- and sphingolipids of biological origin using a mobile phase containing phosphoric acid leads to gradual hydrolysis of plasmalogens during their passage through the column. The resulting 2-acyl lyso analogues give rise to peaks that tail in the direction of the parent intact plasmalogen. Tailing can be prevented by previous complete acid hydrolysis of plasmalogens. Direct high-performance liquid chromatographic profiling of phospholipids, their plasmalogens (as 2-acyl lyso analogues) and sphingolipids is probably the method of choice for the diagnosis of patients with deficient plasmalogen biosynthesis caused by peroxisomal abnormalities.     

Preparation and properties of anionic transition metal complexes containing triheterocarbenium ions

Summary Thermally stable anionic tetracarbonylcobalt complexes containing triheterocarbenium ions, [Co(CO)₄]^–[cation]⁺, have been synthesized by the ion exchange reaction of [Co(CO)₄]^–PPN⁺ with the corresponding carbenium ions. Similar molybdenum complexes containing cyclopentadienyl and carbonyl ligands were also prepared. The complexes were characterized by elemental analyses and by i.r. and n.m.r. spectroscopies. The ionic structures of the complexes are confirmed on the basis of their large electric conductivities.     

Effect of gamma-radiation on Methanosarcina hydrogenase containing transition metal ions

Tracer studies using⁶⁵Zn and⁵⁸Co showed that of the four forms ofMethanosarcina hydrogenases, the A form has about 15% of acid labile zinc, while the hydrogenase D has about 50% of cobalt of the total bound activity in the cell and the other two forms B and C have neither zinc nor cobalt. However, all hydrogenases are known to contain iron, sulfur and probably nickel in trace amounts. All air-oxidized forms of hydrogenases catalyze the reduction of methyl viologen after a finite incubation period. The reduction is revealed by an increase in the absorption peak at 602 nm. On -irradiation, all the four hydrogenases changed to more stable oxidized forms, as indicated by an increase in the optical absorption in the visible region at 405 nm. The irradiated samples showed a greater time lag before they could reduce methyl viologen, the time lag increasing with the -dose. The irradiated enzymes could be reactivated by flushing with H₂. The zinc-bearing hydrogenase A alone appeared to be immune to -radiation in its ability to reduce methyl viologen. This may be due to the zinc having no unpaired electrons to interact with -radiation or the primary radiolytic products.     

Iminodiacetic acid functionalised organopolymer monoliths: application to the separation of metal cations by capillary high-performance chelation ion chromatography

Lauryl methacrylate-co-ethylene dimethacrylate monoliths were polymerised within fused silica capillaries and subsequently photo-grafted with varying amounts of glycidyl methacrylate (GMA). The grafted monoliths were then further modified with iminodiacetic acid (IDA), resulting in a range of chelating ion-exchange monoliths of increasing capacity. The IDA functional groups were attached via ring opening of the epoxy group on the poly(GMA) structure. Increasing the amount of attached poly(GMA), via photo-grafting with increasing concentrations of GMA, from 15 to 35 %, resulted in a proportional and controlled increase in the complexation capacity of the chelating monoliths. Scanning capacitively coupled contactless conductivity detection (sC⁴D) was used to characterise and verify homogenous distribution of the chelating ligand along the length of the capillaries non-invasively. Chelation ion chromatographic separations of selected transition and heavy metals were carried out, with retention factor data proportional to the concentration of grafted poly(GMA). Average peak efficiencies of close to 5,000 N/m were achieved, with the isocratic separation of Na, Mg(II), Mn(II), Co(II), Cd(II) and Zn(II) possible on a 250-mm-long monolith. Multiple monolithic columns produced to the same recipes gave RSD data for retention factors of <15 % (averaged for several metal ions). The monolithic chelating ion-exchanger was applied to the separation of alkaline earth and transition metal ions spiked in natural and potable waters.     

Adsorption of heavy metal ions by immobilized phytic acid

Applied Biochemistry and Biotechnology - Phytic acid (myoinositol hexaphosphate) or its calcium salt, phytate, is an important plant constituent. It accounts for up to 85% of total phosphorus in...     

Investigation of adsorption purification of the effluences containing heavy metal ions

Kinetics of adsorption purification of effluences containing heavy metal ions and adsorption of the metal ions under dynamic conditions using various adsorbents, including the products from industrial wastes are studied.     

Dynamic combinatorial libraries for the recognition of heavy metal ions

We present the use of hydrazone dynamic combinatorial libraries (DCLs) to identify macrocyclic receptors that are selective for alkaline earth metal ions over alkali metal ions. In particular, the toxic heavy metal ions Sr(2+) and Ba(2+) induce characteristic changes in the DCLs. Four macrocycles were isolated and characterised by LCMS, HRMS, NMR and X-ray crystallography; binding studies by UV-Vis spectroscopy confirm the selectivity observed in the DCLs.     

Cation-exchange chromatography of some metal ions using aqueous NH4SCN-organic solvent mixtures

Summary Systematic cation-exchange studies of 19 metal ions have been made in various concentrations of NH₄SCN in 4060 organic solvent-water mixtures. The exchange behaviour of the ions depends on the solvent employed. Most of the metal ions show decreasing distribution coefficients with increasing concentration of ammonium thiocyanate in the solvent. Based on the variation of distribution coefficients as a function of NH₄SCN concentration, separations could be predicted and subsequently column chromatographic separations involving Zn, Hg(II), Mg, Mn(II), Co(II), Ni(II), Cd(II), Ce(III), Fe(III), La and Th(IV) were achieved.     

Functionalized SBA-15 mesoporous silica in ion chromatography of alkali,alkaline earths,ammonium and transition metal ions

The retention properties of a SBA-15 mesoporous silica functionalized with –(CH₂)₃COOH groups, synthesized by a co-condensation route, were investigated for the ion chromatography of different cationic species. A systematic study on the effect of different eluent compositions containing non-complexing (methanesulfonic acid) or complexing (oxalic or pyridine-2,6-dicarboxylic acids) eluents, in the presence of organic modifiers (CH₃CN, CH₃OH, CH₃NH₂) on the retention of cations (Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺, NH₄⁺, Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Pb²⁺, Fe³⁺) chosen as model analytes and for their environmental importance, allowed us to elucidate the mechanisms (cation-exchange or complexation) involved in the retention on the SBA-15 phase. For the first time separations of cations on SBA-15 based stationary phases are investigated, providing the basis for further development of mesoporous silica chemistry for in-flow ion-exchange applications.     

Peptide mapping with liquid chromatography using a basic mobile phase

A new peptide mapping with liquid chromatography (LC) using an ammonia-containing basic mobile phase was reported. As compared with a method under a traditional acidic condition with a mobile phase containing trifluoroacetic acid (TFA) or formic acid (FA), the new method exhibited excellent overall performance: it was advantageous over the TFA method in terms of the ultraviolet (UV) and mass spectrometry (MS) sensitivities and the sequence coverage for a tryptic map; it was superior to the FA method in terms of the UV sensitivity, the sequence coverage and the separation capacity. Due to a significant difference in the chromatographic selectivity, several important peptide mapping applications that were sometimes difficult to be conducted previously could now be carried out using the new method. For example, the baseline separation of peptides from the corresponding deamidated products could be achieved with confidence using the new method, a critical pre-requisite for definitive identification and quantification of the deamidation products with LC/MS. No on-column deamidation was observed with the conditions used for the separation. Complementary and confirmative information about a protein could be obtained by running its proteolytic digest under both the basic and acidic conditions.