Retention of alkali,alkaline earth and transition metals on an itaconic acid cation-exchange column. Eluent pH,ionic strength and temperature effects upon selectivity

The unusual selectivity of a methylene succinic (itaconic) acid modified polymeric column was investigated for the separation of alkali, alkaline earth, transition and heavy metals employing non-chelating inorganic eluents. The retention of selected metal ions on the column was investigated with simple HNO3 eluents and eluents prepared from KNO3 and KCl salts of varying pH (adjusted using HNO3). From these studies both the effect of eluent ionic strength and pH upon retention was evaluated for the itaconic acid stationary phase. The results obtained showed that despite slow exchange kinetics causing poor efficiencies, acceptable baseline separations of selected alkaline earth and transitions could be obtained under optimum conditions (the baseline separation of Mg(II), Ca(II), Mn(II), Cd(II), Zn(II) and Co(II) was possible using a 15 mM KNO3-5 mM KCl eluent at pH 3.50 in under 25 min). The use of an simple ionic strength step gradient was shown that facilitated the addition of Pb(II) to the above group of metal ions. An investigation into the effect of temperature upon peak efficiency and retention showed increased column temperature could be used to improve the resolution of closely eluting metal ions such as Ca(II) and Sr(II) and Ca(II) and Mn(II).     

Iminodiacetic acid functionalised monolithic silica chelating ion exchanger for rapid determination of alkaline earth metal ions in high ionic strength samples

Iminodiacetic acid has been covalently bonded to a bare silica monolith to produce the first reported high-performance monolithic chelating ion exchange column. Using the new column, separation and determination of traces of alkaline earth metal ions (low ppm) in high ionic strength samples (up to 2 M NaCl and KCl brines), could be achieved in under 40 s. At an eluent flow rate of 4 mL min(-1) retention time precision was < 1.2% (n = 9) for Mg(II) and Ca(II), with detector linearity (n = 5) over the range 2-10 mg L(-1) of between R2 = 0.985 and R2 = 0.995. In 1 M KCl and NaCl brine samples, detection limits of 0.2 mg L(-1) were possible.     

On-line coupling of supercritical fluid extraction with high-performance liquid chromatography for the determination of explosives in vapour phases

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).     

Thin-layer chromatographic behavior and separation of alkaline earth metals on silica gel in aqueous sodium perchlorate solution

The thin-layer chromatographic behavior of alkaline earth metal ions (Mg2+, Ca2+, Sr2+, and Ba2+) in aqueous sodium perchlorate solutions on silica gel thin-layers impregnated with sodium hydroxide has been surveyed as a function of salt concentration. At salt concentrations above 2 mol 1(-1), the selectivity of the metals increased with a decrease in the crystal ionic radii; with further increases in salt concentration, the selectivity differences among the metals expanded remarkably. In the present systems, it was supposed that the cation exchange, the surface complexation, and the salting-out effect participate simultaneously in the adsorption of the metals on silica gel. Typical chromatograms for the mutual separation of the alkaline earth metals are presented.     

An ion-exchange separation of metal cations on a C-18 column coated with dodecylsulphate

The retention mechanism was studied for the cations of the alkaline earth metals and Zn(2+) Ni(2+), Co(2+), Cd(2+) and Bi(3+) on a C(18) column permanently coated with sodium dodecylsulphate, with aqueous mobile phases containing cupric chloride or sulphate, or cerous nitrate. The dependencies of the logarithm or the capacity ratio on the logarithm of the eluent concentration were linear, demonstrating that ion-exchange was the predominating separation mode; the slopes of these dependencies were in good agreement with the values predicted from the ion-exchange theory. Indirect UV photometric detection yielded limits of detection (LOD) of 21, 44, 120 and 275 ng in the volume injected, 20 mul, for Mg(2+), Ca(2+), Sr(2+) and Ba(2+), respectively, with the 10(-2)M copper(II) chloride mobile phase; the respective LOD values decreased to 0.8, 1.6, 3.0 and 6.7 ng with the 5 x 10(-4)M cerium(III) nitrate eluent. The method was found to be primarily suitable for determination of the alkaline earths and was applied to analyses of surface and mineral waters.     

A molecular dynamics study of alkaline earth metal-chloride complexation in aqueous solution

The relative stability of alkaline earth metals (M2+ = Mg2+, Ca2+, Sr2+, and Ba2+) and their chloride complexes in aqueous solution is examined through molecular dynamics simulations using a flexible SPC water model with an internally consistent set of metal ion force field parameters. For each metal-chloride ion pair in aqueous solution, the free energy profile was calculated via potential of mean force simulations. The simulations provide detailed thermodynamic information regarding the relative stability of the different types of metal-chloride pairs. The free energy profiles indicate that the preference for contact ion pair formation increases with ionic radius and is closely related to the metal hydration free energies. The water residence times within the first hydration shells are in agreement with residence times reported in other computational studies. Calculated association constants suggest an increase in metal-chloride complexation with increasing cation radii that is inconsistent with experimentally observed trends. Possible explanations for this discrepancy are discussed.     

单一阴离子交换柱同时分离有机酸和无机阴阳离子

研究了用乙二胺四乙酸（ＥＤＴＡ）作淋洗液时，性质迥异的有机酸、无机阴离子和碱土金属离子（Ｃａ＾２＋、Ｍｇ＾２＋）在同一阴离子交换柱上的同时分离以及保留机理，结果表明，在离子交换机理之外，非离子交换机理对有机酸及钙镁的ＥＤＴＡ络阴郭的保留行为起一定的辅助作用，９种有机酸和无机阴阳离子在１０ｍｉｎ内得到了较好的分离。各离子的电导检测灵敏度在１０＾－９至１０＾－１１ｍｏｌ，能满足环境和食吕分析的要求。     

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.     

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.     

The importance of cerium substituted phosphates as cation exchanger-some unique properties and related application potentials

Seven different samples of an inorganic ion exchanger, cerium phosphate, suitable for column use have been prepared under varying conditions. The property of these exchangers has been characterized by Inductively Coupled Plasma Spectroscopy. These exchangers are stable in water, dilute mineral acids, ethanol, methanol, acetone and ether. However, in concentrated HCl and HNO(3) they decompose. They retain about 50% of their exchange value after drying at 80 degrees C, and can be regenerated twice without any decrease in exchange capacity. The distribution coefficient measurements for alkaline earth metals, tellurium, iodine and molybdenum using these seven ion exchangers were studied. This revealed the relative affinity for each exchanger, where the sorption in general was most effective at pH 6-8. The titration curves of cerium phosphate (disodium) with alkaline earth metals showed that the selectivity sequence Ba(2+)>Sr(2+)>Ca(2+)>Mg(2+) is observed. Furthermore, it could be deduced that the adsorption of alkaline earth metal cations greatly depends on the cation. These studies have also shown that cerium phosphates with divalent ions are strongly preferred to monovalent ones. Therefore, as for the cerium phosphates with large monovalent ions, the lack of exchange for Ba(2+), Mg(2+) or other alkali earth metal ions should be essentially due to steric hindrance and this could include any one of the following: the large crystalline radius of metal ions or large hydrated ionic radius and high energy of hydration for other divalent ions. Three binary separations of Te(IV)-Mo(VI), Te(IV)-I(I) and Mo(VI)-I(I) has been developed and the recovery ranging from 90 to 100% has been achieved on cerium phosphate (disodium) columns.     

A potentiometeric study of protonation and complex formation of xylenol orange with alkaline earth and aluminum ions

Xylenol orange (XO) is one of the complexometric indicators, that can bind to metal cations at both their amino and acidic groups. In this study the protonation constants and distribution diagrams of XO were studied pH-metrically, and the corresponding six protonation constants were calculated. The complex formation between XO (L) and alkaline earth ions (M) was investigated and the formation constants of the resulting complexes ML, MHL, M(2)L and M(2)HL were determined. The stabilities of both ML and M(2)L complexes were found to vary in the order Mg(2+)> Ca(2+)> Sr(2+)> Ba(2+). Studying the complex formation between Al(3+) ion (M) and XO (L), it was observed that four complexed species with stoichiometries ML, ML(2), MHL and MH(2)L could be formed in solution. It was also found that the Al L(2) complex can act as a chelating agent for further complexation with two cations other than Al(3+) ion (i.e. Ba, L, Al, L, Ba, Mg, L, Al, L, Mg, and Mg, L, Al, L, Ba). The formation constants of the resulting mixed complexes were determined and their distribution diagrams were investigated.     

Helical metallohost-guest complexes via site-selective transmetalation of homotrinuclear complexes

We have designed a new type of bis(N2O2) chelate ligand that affords a C-shaped O6 site on the metalation of the N2O2 sites. UV-vis and 1H NMR titration clearly showed that the complexation between H4L and zinc(II) acetate affords 1:3 complex [LZn3]2+ via a highly cooperative process. Although the O6-recognition site of the dinuclear metallohost [LZn2] is filled with the additional Zn2+, the O6 site can bind a guest ion with concomitant release of the initially bound Zn2+. The novel recognition process "guest exchange" took place quantitatively when rare earth metals were used as a guest. In the case of alkaline earth metals, selectivity of Ca2+ > Sr2+ > Ba2+ > Mg2+ was observed. On the other hand, the transmetalation did not take place at all when alkali metals were used for the guest. Accordingly, the trinuclear complex [LZn3]2+ is excellent in discriminating charge of the guest ions. The metallohost-guest complexes thus obtained have a helical structure, and the radius d and winding angle theta of the helix depend on the size of the guest. The La3+ complex has the smallest theta (288 degrees), and the Sc3+ complex has the largest theta (345 degrees). Because the radius and winding angles of helices are tunable by changing the guest ion, the helical metallohost-guest complexes are regarded as a molecular spring or coil. Consequently, site-specific metal exchange of trinuclear complex [LZn3]2+ described here will be utilized for highly selective ion recognition, site-selective synthesis of (3d)2(4f) trimetallic complexes, and construction of "tunable" metallohelicenes.     

Infrared spectra and electronic structure calculations for the group 2 metal M(OH)2 dihydroxide molecules

Reactions of laser-ablated Mg, Ca, Sr, and Ba atoms with O2 and H2 in excess argon give new absorptions in the O-H and O-M-O stretching regions, which increase together upon UV photolysis and are due to the M(OH)2 molecules (M = Mg, Ca, Sr, and Ba). The same product absorptions are observed in the metal atom reactions with H2O2. The M(OH)2 identifications are supported by isotopic substitution and theoretical calculations (B3LYP and MP2). The O-H stretching frequencies of the alkaline earth metal dihydroxide molecules decrease from 3829.8 to 3784.6 to 3760.6 to 3724.2 cm(-1) in the family series in solid argon, while the base strength of the solid compounds increases. Calculations show that Sr(OH)2 and Ba(OH)2 are bent at the metal center, owing to d orbital involvement in the bonding. Although these molecules are predominantly ionic, the O-H stretching frequencies do not reach the ionic limit of gaseous OH- going down the family group because of cation-anion polarization and p(pi) --> d(pi) interactions.     

Effective interaction potentials for alkali and alkaline earth metal ions in SPC/E water and prediction of mean ion activity coefficients

The potential of mean force (PMF) acting between two simple ions surrounded by SPC/E water have been determined by molecular dynamics (MD) simulations using a spherical cavity approach. Such effective ion-ion potentials were obtained for Me-Me, Me-Cl-, and Cl(-)-Cl- pairs, where Me is a Li+, Na+, K+, Mg2+, Ca2+, Sr2+, and Ba2+ cation. The ionic sizes estimated from the effective potentials are not pairwise additive, a feature in the frequently used primitive model for electrolytes. The effective potentials were used in Monte Carlo (MC) simulations with implicit water to calculate mean ion activity coefficients of LiCl, NaCl, KCl, MgCl2, CaCl2, SrCl2, and BaCl2. Predicted activities were compared with experimental ones in the electrolyte concentration range 0.1-1 M. A qualitative agreement for LiCl and a satisfactory agreement for NaCl were found, whereas the predictions for KCl by two K+ models were less coherent. In the case of alkaline earth metal ions, all experimental activities were successfully reproduced at c = 0.1 M. However, at higher concentrations, similar deviations occurred for all divalent cations, suggesting that the dependence of the permittivity on the salt concentration and the polarization deficiency arising from the ordering of water molecules in the ion hydration shells are important in such systems.     

高锰酸钾-鲁米诺反应体系中碱土金属离子Mg2+,Ca2+,Sr2+,Ba2+化学发光行为研究

将被认为没有化学发光活性的第二主族(碱土金属)离子Mg^2 ,Ca^2 ,Sr^2 ,Ba^2 溶液注入到已充分反应的高锰酸钾与鲁米诺混合液中时,又发生了新的化学发光反应,并检测到强的化学发光信号．在对有关反应的动力学性质、化学发光光谱、紫外可见光谱及其它一系列实验研究的基础上,提出了可能的化学发光反应机理．同时,优化了反应条件,评价了这一反应用于Mg^2 ,Ca^2 ,Sr^2 ,Ba^2 分析的可行性．     

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.     

Tandem mass spectra of divalent metal ion adducts of glycosyl sulfides, sulfoxides and sulfones; distinction among stereoisomers

The tandem mass spectra of the divalent metal ion (Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Ni2+, Co2+ and Zn2+) adducts of acetylated 1,2-trans-glycosyl sulfides, sulfoxides and sulfones were examined using low energy collision-induced dissociation on a Quattro II quadrupole tandem mass spectrometer. Abundant doubly charged ions, such as [3M + Met]2+ and [2M + Met]2+, were observed with alkaline earth metal chlorides. The other ions observed were [M + MetCl]+, [M + MetOAc]+, [M + MetO2SPh]+ and [2M + MetCl]+. The deprotonated metal adducts [M + Met-H]+ were seen only in the sulfones. The divalent metal ion adducts showed characteristic fragmentation pathways for the glycosyl sulfides, sulfoxides and sulfones, depending on the site of metal attachment. The doubly charged metal ion adducts dissociate to two singly charged ions, [M + MetOAc]+ and [M - OAc]+, in the sulfides and sulfoxides. In the sulfones, the adducts dissociate to [M + MetO2SPh]+ and [M - O2SPh]+. In contrast to the alkaline earth metals, which attach to the acetoxy functions, the transition metals attach to the sulfide and sulfoxide functions. The metal chloride adducts display characteristic fragmentation for the sulfides, sulfoxides and sulfones. The glucosyl, mannosyl and galactosyl sulfides, sulfoxides and sulfones could be differentiated on the basis of the stereochemically controlled MS/MS fragmentations of the metal chloride adducts.     

Synthesis and structures of monomeric magnesium, calcium, strontium, and barium amides involving the N,N-(2,4,6-trimethylphenyl)(trimethylsilyl)amido ligand

An extended family of aryl-substituted alkaline earth metal silylamides M{N(2,4,6-Me3C6H2)(SiMe3)}donor(n) was prepared using alkane elimination (Mg), salt elimination (Ca, Sr, Ba), and direct metalation (Sr, Ba). Three different donors, THF, TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), and PMDTA (PMDTA = N,N,N',N',N'-pentamethyldiethylenetriamine) were employed to study their influence on the coordination chemistry of the target compounds, producing monomeric species with the composition M{N(2,4,6-Me3C6H2)(SiMe3)}2(THF)2 (M = Mg, Ca, Sr, Ba), M{N(2,4,6-Me3C6H2)(SiMe3)}2TMEDA (M = Ca, Ba), and M{N(2,4,6-Me3C6H2)(SiMe3)}2PMDTA (M = Sr, Ba). For the heavier metal analogues, varying degrees of agostic interactions are completing the coordination sphere of the metals. Compounds were characterized using IR and NMR spectroscopy in addition to X-ray crystallography.     

Synthesis and study of uranoborates M k (BUO5) k · nH2O (M k is alkaline, alkaline-earth, or 3d metal)

A series of uranoborates of alkaline (Li, Na, K, Rb, Cs), alkaline-earth (Mg, Ca, Sr, Ba), and 3d transition (Mn, Co, Ni, Zn) metals was synthesized by solid-phase reactions and ion exchange. The compositions and structures of these borates were examined using X-ray diffraction, IR spectroscopy, and thermal analysis. It is found that they have phase and functional similarities and belong to the group of layered uranium compounds.     

Determination of ion exchange equilibrium constants of strongly acidic resins with alkaline-earth metals by means of the potentiometric titrations technique

A recently developed methodology for the determination of ion exchange equilibrium constants has been applied to ion exchange systems of 1:2 stoichiometry. Potentiometric titrations with variable ionic strength were carried out. Ionic medium titrations were performed for the estimation of the liquid junction potential. The modified Bromley's methodology and the Wilson model were used for the estimation of the activity coefficients of the species in the aqueous and resin phase, respectively. A modification of the Henderson equation is used for the estimation of liquid junction potentials in the mixtures including 1:2 electrolytes. Equilibrium constants for the H(+)/M(2+) (M=Mg, Ca, Sr and Ba) exchange systems in the strongly acidic resins Dowex CM-15 and Dowex C650 were studied.