Determination of Ca, Mg, Fe and Zn partitioning in UHT cow milks by two-column ion exchange and flame atomic absorption spectrometry detection

An operationally defined fractionation protocol was developed to study the partitioning of Ca, Mg, Fe and Zn in UHT cow milks. The method was based on sorption of distinct metal species by two ion exchange columns, namely strong cation exchanger Dowex 50Wx4 and strong anion exchanger Dowex 1x4, connected in a series. The evaluation of the donation of metal species classes distinguished, that is cationic and anionic fractions, was made after splitting the columns and elution of metal groupings with a 2.0 mol l⁻¹ HCl solution, followed by the determination of metal concentrations in the resulting eluates. The amount of third, inert fraction was assessed by measuring metal contents in the effluents obtained after passage of the samples through the columns. The results achieved utilizing two-column ion exchange based procedure were compared with those obtained for the approach in which the columns were considered separately. The fractionation pattern for each metal studied was thoroughly discussed in light of available knowledge relating to the composition of milk.     

Simple and versatile operational fractionation of Fe and Zn in dietary products by solid phase extraction on ion exchange resins

A simple and versatile protocol, based on use of solid phase extraction on strong ion exchangers and off-line detection by flame atomic absorption spectrometry, was devised to fractionate iron and zinc in common dietary food and beverages products, i.e., bee honeys, fruit juices and tea infusions. In the procedure proposed, cation exchanger Dowex 50Wx4 and anion exchanger Dowex 1x4 were used separately for distinguishing broadly meant the cationic metal fraction and the fraction of stable anionic metal complexes, respectively, after retention of metal species and their exhaustive elution by means of a 4.0 mol l⁻¹ HCl solution. The third fraction, referred to the residual metal species, was retrieved by difference between total soluble metal contents and sum of metal quantities in separated cationic and anionic fractions. The fractionation pattern observed for both metals was described and discussed.     

Preconcentration and Fractionation of Cd, Co, Cu, Ni, Pb and Zn in Natural Water Samples Prior to Analysis by Inductively Coupled Plasma Atomic Emission Spectrometry

The strong cation exchanger Dowex 50W-x4 was used for the enrichment of traces of Cd, Co, Cu, Fe, Ni, Pb and Zn in mineral and mine waters as an alternative to the commonly applied procedures based on the application of chelating resins. The resin used was found suitable for complete retention of these metals both from the solutions of very low pH as well as those close to neutral, thus eliminating the need to buffer the samples. An analytical scheme based on filtration and solid phase extraction with Dowex 50W-x4 was proposed for partitioning Cd, Co, Cu, Fe, Ni and Pb in the examined waters. The fraction of metals associated with the suspended particles was determined after filtration through a 0.45 µm pore size filter and decomposition of the deposited matter. For the evaluation of fractions of the labile metal species and the total dissolved metals, the untreated filtrates and the solutions resulting from their digestion, respectively, were passed through Dowex 50W-x4 cation exchange columns. The retrieval of the metals was completed using a 4.0 mol L⁻¹ solution of HCl. The described metal preconcentration and fractionation protocol offered the enrichment factor of 25 with detection limits equal to 22, 30, 92, 41, 70, 36 and 340 ng L⁻¹, respectively for Cd, Co, Cu, Fe, Ni and Pb. Reasonably good precision and accuracy were attained.     

Fractionation analysis of magnesium in olive products by atomic absorption spectrometry

A scheme is presented for fractionation of olive components and magnesium determinations in different fractions. The charge of metal species was established using cation exchange with Dowex 50Wx8-40. The resin Amberlite XAD-4 was used for the separation of olive polyphenols in complexes with olive proteins and polysaccharides. The organic and inorganic fraction of magnesium was studied with different solvents as to its bioavailability properties. Flame and electrothermal atomic absorption spectrometry were used off-line for the determinations of magnesium in the different fractions obtained.     

Manganese and zinc operational fractionation in beer by means of tandem ion exchange column assemblage and flame atomic absorption spectrometry

A straightforward method is presented for the operational fractionation of Mn and Zn in beer based on use of a tandem ion exchange column assemblage. Degassed beer samples were driven through the system comprising the weak anion exchanger Reillex 402 (first column) connected in a series with the strong cation exchanger Dowex 50Wx4 (second column). The relevant metal groupings retained on the exchangers, i.e., the fraction of the metals bound to the polyphenols, and the fraction of the cationic metal species, were determined respectively in the effluents (5-mL portions) sampled during the passage of the samples through the first column, and in the eluates obtained by the elution of Mn and Zn species (with 10 mL of 4.0 mol L⁻¹ HCl) from the second column, after passing the samples through the tandem column system. Additionally, the effluents obtained after loading the tandem column system with the samples were also collected and taken to the analysis in order to asses the donation of the third, residual fraction. The usefulness of the fractionation scheme is illustrated by the analysis of three bottled beers produced by a local brewery. The fractionation patterns established for Mn and Zn are discussed regarding the possible associations of the metals under consideration with different endogenous beer ligands.     

Direct Determination of the Total Concentrations of Magnesium,Calcium, Manganese,and Iron in Addition to their Chemical and Physical Fractions in Dark Honeys

The present work demonstrates a very simple and rapid method for the reliable determination of total concentrations of Mg, Ca, Mn, and Fe in dark honeys by means of flame atomic absorption spectrometry without any special sample pretreatment except for dissolution in water. An analytical scheme for the partitioning of Mg, Ca, Mn, and Fe in analyzed honeys was proposed as well. For a complementary evaluation of fractionation patterns for studied metals, a two linked column solid phase extraction procedure with a nonionic adsorbing resin Amberlite XAD-16 and a strong cation exchange resin Dowex 50 W × 8–200 in addition to an ultrafiltration procedure with five membranes having molecular weight cut-offs of 5, 10, 30, 50, and 100 kDa were used. In the course of the fractionation analysis, it was found that the most dominant group of species is the one containing cationic forms of metals bound to low molecular weight (<5 kDa, 5–10 kDa) natural honey bioligands and is mostly the case of simple ions and labile species of Mg, Ca, Mn, and Fe. Correspondingly, the contribution of the cationic fraction for these metals in analyzed dark honeys was up to 96% (Mg), 95% (Ca), 90% (Mn), and 86% (Fe). A significant contribution of the hydrophobic fraction was also established; it was maximally 10, 18, 20, and 25% for Mg, Ca, Mn, and Fe, respectively.     

Fractionation and speciation of Cu,Zn and Fe in wine samples by atomic absorption spectrometry

A scheme is presented for fractionation of wine components and Fe, Cu and Zn determination in different fractions. The charge of the metal species was established using cation and anion exchange separation based on solid phase extraction. The resin XAD-8 was used for the separation of wine polyphenols in complexes with wine proteins and polysaccharides. Dowex ion exchange resins were used for the separation of cationic and anionic species of Fe, Cu and Zn. Flame atomic absorption spectrometry and electrothermal atomic absorption spectrometry were used off-line for the quantitative determination of metals in the different fractions obtained.     

Removal of iron, copper and manganese from white wines through ion exchange techniques: effects on their organoleptic characteristics and susceptibility to browning

Ion exchange techniques have been used to reduce the content of iron, copper and manganese in white wines. Two exchanger resins have been compared, a chelating resin, the active group of which is iminodiacetate and a Dowex, acidic cation exchange resin.The results obtained show that the technique of using exchanger resins is extremely effective in lowering the metal content of wines, although on occasions, their use alters the organoleptic characteristics of the wine. Treated wines present lower polyphenolic and aromatic profiles than the untreated wines. Polyphenolic and metallic reductions would explain why treated wines present a notably reduced susceptibility to browning.     

Fractionation analysis of manganese and zinc in beers by means of two sorbent column system and flame atomic absorption spectrometry

In the present article, a method of operational fractionation of Mn and Zn in beer using flame atomic absorption spectrometry was developed. The proposed fractionation scheme was based on use of a hydrophobic adsorbing resin Amberlite XAD7 (first column, 2 g resin bed) connected in a series with a strong cation exchanger Dowex 50Wx4 (second column, 1 g resin bed). After passing the samples of beers through the columns, distinct groupings of Mn and Zn species retained on the sorbents, i.e., hydrophobic fraction of polyphenols bound metal species and cationic metal species fraction, respectively, were determined in respective eluates obtained after complete recovery of Mn and Zn species with 10 ml of 2.0 mol l⁻¹ HNO₃ (first column) and 10 ml of 4.0 mol l⁻¹ HCl (second column). In addition, the effluents collected were analyzed prior to the evaluation of the third, residual fraction, presumably attributed to any hydrophilic anionic and inert metal species. The established fractionation patterns for Mn and Zn were discussed in reference to likely associations of metals with endogenous food bioligands and possible availability of the distinguished metal species classes. The quality of the results was proved by the recovery experiments.     

Uptake of iodine and bromine by ion-exchange resins in aqueous solution

The uptakes of molecular iodine and bromine by both strong acid cation (Dowex 50W-X4 and X8) and strong base anion (Dowex 1-X4 and X8) exchange resins have been studied in aqueous solutions at 25 degrees C. An empirical formula for the amount of solute taken up by the resin in mmol per gram of dry resin, Q, as a function of the solute concentration in M (mol dm(-3)), C, was derived. Direct proportional relationships between Q and C have been found, except for the bromine-anion exchanger system. In contrast to the cation-exchange resin, the anion exchanger exhibits extremely high affinity for I(2) and Br(2).     

Manual and automated enrichment procedures for biological samples using lipophilic gels

Aspects of the use of lipophilic gels in manual sample preparation procedures are reviewed. Neutral gels with a controlled hydrophobicity are used for sorbent extraction of non-polar and medium polarity compounds from biological fluids. Acidic amphiphilic compounds can be extracted as ion-pairs with decyltrimethylammonium ions. Solvent or detergent extracts of tissues or faeces can be mixed with hydrophobic gels for transfer of analytes from a solvent to a gel phase, permitting subsequent sample preparation in gel bed systems. Hydrophobic gels, alkyl-bonded silica and polystyrene matrices can be used in series for extraction of compounds with a wide range of polarities. Group fractionations are performed on neutral and ion-exchanging lipophilic gels to yield fractions of neutral, basic and acidic metabolites within selected polarity ranges. Selective isolation of phenolic acids on a strong anion exchanger, of ethynylic steroids on a strong cation exchanger in silver form and of oximes of ketonic steroids on a strong cation exchanger in hydrogen form is possible. A computerized system for automatic sample preparation is also described. It consists of an extraction bed, a cation-exchange column and an anion-exchange column. The pumps and switching valves are arranged so that the columns can operate in series or parallel for isolation of neutral, basic and acidic metabolites of amphiphilic compounds and for regeneration of the column beds. Fractions can be collected, or the effluent from the column beds can be diluted with water to permit sorption on a solid phase. The applicability of the automated method to the analysis of bile acids and metabolites of mono(2-ethylhexyl) phthalate is demonstrated.     

The role of organic acids on <Superscript>226</Superscript>Ra transfer factor in corn (<Emphasis Type="Italic">Zea mays</Emphasis> L.)

Enrichment of lithium isotopes by displacement chromatography on strong acid cation exchanger was investigated. Narrow particle fraction of Dowex 50 WX 2 cation exchanger having diameter of 150–200 µm and total exchange capacity of 1.31 meq mL^?1 was used as stationary phase. As a mobile phase, 1 mol L^?1 solution of ammonium nitrate solution was used. Shape and position of Li chromatographic peak, was determined by atomic emission spectroscopy (AES). Isotope ratio was estimated by ICP–MS after 1, 8 and 10 enrichment steps. Value of separation factor for ⁶Li in one step was determined to be 1.027.     

离子交换分离富集和ICP-AES测定钨酸钠中微量钙和镁

本文首次提出了用ICP-AES法测定用D001-CC强酸型阳离子交换树脂预分离富集钨酸钠中Ca和Mg。Ca及Mg的平均口收率分别为95%及90%,相对偏差分别为1.8%及0.9%。     

Cation-exchange separation of uranium from other elements in tetrahydrofuran-nitric acid media containing trioctylphosphine oxide

The batch distribution coefficients of Cu(II), Za, Cd, Fe(III), Hg(II), Mg, Co(II), Ni, Pb, Ca and Bi were determined on the strongly acidic cation-exchange resin Dowex 50 x 8 in 0.1M trioctylphosphine oxide in tetrahydrofuran-5% 12M nitric acid. In this mixture all these metal ions, except Bi, have high K(d)-values and can be separated quantitatively from uranium which has a distribution coefficient of 0.1. Mixtures of U with Cu, Ni, Co, Cd or Fe were analysed to test the applicability of such separations. Different titrimetric and spectrophotometric methods were used to determine the elements subsequent to their separation from uranium on ion-exchange columns. The results show that accurate and effective separations can be achieved.     

A controlled supramolecular approach toward cation-specific chemosensors: alkaline earth metal ion-driven exciton signaling in squaraine tethered podands

Three different squaraine tethered bichromophoric podands 3a-c with one, two, and three oxygen atoms in the podand chain and an analogous monochromophore 4a were synthesized and characterized. Among these, the bichromophores 3a-c showed high selectivity toward alkaline earth metal cations, particularly to Mg(2+) and Ca(2+) ions, whereas they were optically silent toward alkali metal ions. From the absorption and emission changes as well as from the Job plots, it is established that Mg(2+) ions form 1:1 folded complexes with 3a and 3b whereas Ca(2+) ions prefer to form 1:2 sandwich dimers. However, 3c invariably forms weak 1:1 complexes with Mg(2+), Ca(2+), and Sr(2+) ions. The signal output in all of these cases was achieved by the formation of a sharp blue-shifted absorption and strong quenching of the emission of 3a-c. The signal transduction is achieved by the exciton interaction of the face-to-face stacked squaraine chromophores of the cation complex, which is a novel approach of specific cation sensing. The observed cation-induced changes in the optical properties are analogous to those of the "H" aggregates of squaraine dyes. Interestingly, a monochromophore 4a despite its binding, as evident from (1)H NMR studies, remained optically silent toward Mg(2+) and Ca(2+) ions. While the behavior of 4a toward Mg(2+) ion is understood, its optical silence toward Ca(2+) ion is rationalized to the preferential formation of a "Head-Tail-Tail-Head" arrangement in which exciton coupling is not possible. The present study is different from other known reports on chemosensors in the sense that cation-specific supramolecular host-guest complexation has been exploited for controlling chromophore interaction via cation-steered exciton coupling as the mode of signaling.     

Labile metal content of sediments-fractionation scheme based on ion-exchange resins

The labile metal content of sediments can be evaluated by equilibrating sediment suspensions with ion-exchange resins. By use of a sequence of strong-acid and weak-acid cation-exchangers (H(+)- and Na(+)-form) and chelating resins, extraction can be performed at pH values ranging from 2 to 10. The results allow the total metal content to be subdivided into seven categories designated as (i) low-pH labile, (ii) weak-acid labile, (iii) exchangeable and readily desorbed at sediment-suspension pH, (iv) weak-base labile, (v) high-pH labile, (vi) non-labile soluble forms and (vii) detrital metal content. The sediment suspensions are mixed overnight with the different types of exchanger (held in porous containers) and the cations transferred from the sediment are subsequently back-extracted from the resins into 0.05M EDTA (pH 7.5). The EDTA extracts are analysed for Cu, Pb, Zn, Cd, Ca, Mg, Fe and Al. Analysis of the aqueous phase left in contact with the sediment residue gives the amount of non-labile species released. Eighteen sediments, containing various levels of metal contamination, and an effluent dam sludge have been examined by this technique. All the exchangers released Ca and Mg from the sediments, and the H(+)-form exchangers also released Fe and Al. Some of the Fe, Al and to a lesser extent Zn released by the sediment/exchanger interactions was present as non-labile "soluble" species. The advantages and limitations of this "labile metal" fractionation scheme have been considered.     

Cation Exchange Separation of Protactinium from Tantalum with Sulfuric Acid-Alcohol Mixed Solvent System

Distributions of protactinium and tantalum between strongly acidic cation exchange resin and sulfuric acid-mixed organic solvent system were studied with Pa-233 and Ta-182 as radioactive tracers. Methyl, ethyl and isopropyl alcohols were used as miscible organic solvents and Dowex 50 W-X 2, Dowex 50 W-X 12, Bio Rad AG 50 W-X 4 and AG 50 W-X 12 were used for different cross linking cation exchange resin. Distribution ratios were plotted against acidities by keeping compositions constant or against compositions by keeping acidities constant. From these plot tings, different trends of these two metals were found. With the use of the property of especially strong absorption of protactinium in methyl alcohol solution by resin having higher degree of cross linking, AG 50 W-X 12, tantalum could be completely separated from protactinium.     

Fractionation of histones on a metal ion equilibrated cation exchanger. I. Chromatographic profiles on an Amberlite IR-120 (A1 3+) column

Amberlite IR-120, a polystyrene sulphonate type of cation exchanger, equilibrated with A1 3+ ions, has been employed for the fractionation of whole histone. This adsorbent permits the quantitative and reproducible recovery of whole histone in six fractions.     

Ultrafine Na-4-mica: uptake of alkali and alkaline earth metal cations by ion exchange

The cation exchange properties of alkali and alkaline earth metal cations at room temperature were investigated on an ultrafine, highly charged Na-4-mica (with the ideal mica composition Na4Mg6Al4Si4O20F4.xH2O). Ultrafine mica crystallites of 200 nm in size led to faster Sr2+ uptake kinetics in comparison to larger mica crystallites. The alkali metal ion (K+, Cs+, and Li+) exchange uptake was rapid, and complete exchange occurred within 30 min. For the alkaline earth metal ions Ba2+, Ca2+, and Mg2+, however, the exchange uptake required lengthy periods from 3 days to 4 weeks to be completed, similar to its Sr uptake, as previously reported. Kinetic models of the modified Freundlich and parabolic diffusion were examined for the experimental data on the Ba2+, Ca2+, and Mg2+ uptakes. The modified Freundlich model described well the Ba2+ ion uptake kinetics as well as that for the Sr2+ ion, while for the Ca2+ and Mg2+ ions the parabolic diffusion model showed better fitting. The alkali and alkaline earth ion exchange isotherms were also determined in comparison to the Sr2+ exchange isotherm. The thermodynamic equilibria for these cations were compared by using Kielland plots evaluated from the isotherms.     

H+-Ca2+ Equilibrium Exchange on Polyacrylic Cationites

Potentiometric titration curves of carboxyl-containing polyacrylic cation exchangers (Amberlite IRC 86, Dowex MAC 3, Lewatit CNP 80, Purolite C 104, and Relite CNS) in the H form with calcium ions were measured. It was found that the apparent equilibrium constant strongly depended on the composition of resinate solutions, which was indicative of significant deviations of solutions in the cation exchanger gel phase from the ideal behavior. The largest deviations were observed for Dowex MAC 3 ion exchanger, and the smallest, for Amberlite IRC 86. For the other sorbents, the dependences coincided to within measurement errors. The experimental data were treated in terms of six models of the theory of exchange equilibria. The best approximation to titration curves was obtained in terms of the model that suggested the presence of two types of exchange centers in ion exchangers and took into account the influence of the state of three neighboring fixed groups on each spatially separated center. The amounts of centers of all types in the ion exchangers were determined. Differences in the selectivity of the cation exchangers with respect to calcium ions were explained.