Retention Of Anions Research Articles

Sulfonium and phosphonium, new ion-pairing agents with unique selectivity towards polarizable anions

Ion-pair chromatography (IPC) almost universally relies upon ammonium-based ion-pairing agents (IPAs) for anion separations. This work compares tetrabutylammonium (TBA) with tetrabutylphosphonium (TBP) and tributylsulfonium (TBS). To best understand the retention behavior analytes used for characterization of the IPAs spanned the Hofmeister series; from kosmotropic monoanions (iodate, chloride, nitrite) and intermediate anions (nitrate, bromide) to chaotropic ions (perchlorate, thiocyanate, iodide). The studies demonstrate that tetrabutylphosphonium is the most chaotropic IPA, followed by tetrabutylammonium and finally tributylsulfonium is the least chaotropic. In the case of the chaotropic anions, the retention of perchlorate was least with tributylsulfonium, and greatest for tetrabutylphosphonium, with tetrabutylammonium being intermediate. The multivalent kosmotropic anions (sulfate, chromate, thiosulfate) demonstrated unique selectivity changes depending on the kosmotropic/chaotropic nature of the IPA. Demonstrating increases in retention with increasing IPA concentration only with tributylsulfonium, whereas the more chaotropic IPAs universally decreased the retention of the multivalent anions.

Retention profiles and mechanism of anion separation on latex-based pellicular ion exchanger in ion chromatography

A retention model based on stoichiometric approach has been developed in order to describe analyte retention of anions on latex-based pellicular ion exchanger. The chromatographic process entails two stepwise and complex equilibria, first is ion-pair forming of analyte or eluent ion with ion-exchange sites under the effect of electrostatic forces due to the sulfonic layer behind the aminated functional groups of stationary phase. Second component is the ion-exchange between the analyte and eluent ions. As a new parameter of the fractional electrostatic coefficient of the ion exchange capacity was introduced to develop retention profiles of anions. Analysis of the dependence of the capacity factors on the eluent concentrations at different values of fractional coefficient shed light on the possible complex mechanism. Extensive experimental retention data were obtained for 14 anions (formate, acetate, propionate, pyruvate, lactate, chloride, nitrate, oxalate, malonate, succinate, tartarate, fumarate, maleate, sulphate) using hydroxide eluents of varying concentration. The ion-pair formation and ion-exchange selectivity constants for analyte and eluent species are determined using derived retention equation from experimental data by nonlinear iterative calculation. The model was utilized to predict retention data under elution conditions of practical importance. The predicted and obtained retention factors are in good agreement, which confirms the predictive power of the model.

Accumulation of Cu(II) cations in poly(3,4-ethylenedioxythiophene) films doped by hexacyanoferrate anions and its application in Cu 2+-selective electrodes with PVC based membranes

Electrochemical properties of poly(3,4-ethylenedioxythiophene) doped with hexacyanoferrate(II,III) ions (PEDOT(HCF)) were studied in the presence of Cu 2+ ions. Voltammetric and EDAX studies revealed retention of hexacyanoferrate anions in the polymer film and accumulation of Cu(II) cations, as well as formation of solid copper hexacyanoferrate near the polymer surface. Accumulation of Cu 2+ ions was found to be advantageous from the point of view of PEDOT(HCF) applications as a solid contact (ion-to-electron transducer) in all-solid-state Cu 2+-selective electrodes with solvent polymeric polyvinyl chloride (PVC) based membrane, containing Cu 2+-selective ionophore. Binding of Cu 2+ ions in the conducting polymer layer results in analyte ions flux into the transducer phase. Thus, pronounced enhancement of selectivity of the all-solid-state Cu 2+-selective electrode or lower detection limit of the potentiometric response range was achieved, reaching under optimised conditions 10 −7 M CuSO 4.

π(Arene) versus donor ligand complexation in the formation of the heterobimetallic lithium–potassium dianion of ( S)- N-(α-methylbenzyl)allylamine

Reaction of the chiral amine ( S)- N-(α-methylbenzyl)allylamine with n-BuLi in hexane and the subsequent addition of the thus formed lithium amide to n-BuK followed by thf results in the formation and crystallisation of the cyclic heterobimetallic tetramer, {[( S)-α-(PhC(H)Me)(CH 2CH CHK)N]Li · (thf)} 4 ( 1), containing the C-metallated and N-metallated dianion of the chiral amine. The structure reveals a degree of asymmetry derived from competitive binding of K + cations to available thf molecules, π(arene) electrons, and deprotonated allylamine moieties. Solution studies indicate very strong agostic interactions with C–H bonds in the allylamine group and retention of the terminal vinylic anion rather than delocalisation.

Zwitterionic ion chromatography with carboxybetaine surfactant-coated particle packed and monolithic type columns

Both particle packed (25 cm × 0.46 cm I.D. SUPELCOSIL 5 μm C 18) and monolithic type (10 cm × 0.46 cm I.D. Merck Chromolith Performance C 18) reversed-phase substrates were dynamically coated with a carboxybetaine type zwitterionic surfactant ((dodecyldimethyl-amino) acetic acid) and investigated as stationary phases for use in zwitterionic ion chromatography (ZIC). Investigations into eluent concentration and pH were carried out using KCl eluents containing 0.2 mM of the carboxybetaine surfactant to stabilise the column coatings. It was found that eluent concentration decreased anion retention whilst simultaneously increasing peak efficiencies, which may be due to the dissociation of intra- and inter-molecular salts of the carboxybetaine surfactant under higher ionic strength conditions. The Effect of eluent pH was an increase in anion retention with decreased eluent pH due to the increased protonation of the weak acid terminal group of the carboxybetaine, causing both a relative increase in the positive charge of the stationary phase and less repulsion of the anions by the dissociated weak acid group. The carboxybetaine-coated monolithic phase was applied to rapid anion separations using elevated flow rates and flow rate gradients.

Electrochemically modulated liquid chromatographic separations of inorganic anions

Inorganic anion retention on a porous graphitic carbon (PGC) stationary phase is investigated by electrochemically modulated liquid chromatography (EMLC). Through various combinations of the potential applied (Eapp) to the PGC packing and/or changes in the composition (sodium salts of tetrafluoroborate, sulfate, and fluoride) and concentration (10, 25, and 50mM) of an aqueous mobile phase, conditions for the separation of two different inorganic anion mixtures (iodate, bromide, nitrite, and nitrate or iodate, bromate, and chlorate) are developed. Results show that retention was affected by both variables, with the analyte retention factor, k′, changing in a few cases by as much as a factor of ca. six. Moreover, plots of lnk′ are linearly dependent on both Eapp and ln[SE], where [SE] is the supporting electrolyte concentration. Based on these findings, insights into the retention mechanism are briefly discussed by drawing on the theory for ion exchange chromatography.

Predictive charge-regulation transport model for nanofiltration from the theory of irreversible processes

The charge-regulation concept is combined with the theory of irreversible processes to predict multi-component electrolyte transport in nanofiltration membranes. Charging of the membrane surface is described using a 1-pK site-binding model with a triple-layer electrostatic description. Mass transport is described using Maxwell–Stefan relations, based on the uniform potential approach. A predictive model is resented, which requires no adjustable parameters. Input data is obtained from independent measurements, e.g., electrophoretic mobility data. Model predictions for retention and flux are discussed for an asymmetric γ-alumina nanofiltration membrane for NaCl and a mixture of NaCl with CaCl 2. Double layer overlap in the pores, leading to charge regulation, appears to have a marked influence on the potential across the pore (Δ ϕ = 59–88% for 4 nm pores), and thus on separation. Furthermore, the membrane surface charge and potential vary significantly over the pore length, rendering the assumption of a constant charge and potential generally applied in literature questionable. Additionally, the model predicts typical nanofiltration behaviour, including non-equal cation and anion retention at extreme pH values, dependencies of retention and flux on the permeability and thickness of the top-layer and the support, and the influence of an additional external mass transport resistance. A sensitivity analysis suggests that for an accurate quantitative prediction of the separation behaviour of inorganic NF membranes it is not possible to use more simple descriptions for ion adsorption and mass transport than the 1-pK triple-layer model and the Maxwell–Stefan relations.

Temperature effects on iodine adsorption on organo-clay minerals: II. Structural effects

Smectites and vermiculites modified with hexadecylpyridinium (HDPy +), hexadecyltrimethylammonium (HDTMA +), benzethonium (BE +) and dipyridinododecane (DPyDD 2+) cations exhibit high adsorption capabilities for the anionic radionuclide 125I − (Part I of this article). In some cases, exposure to higher temperature decreased the anion adsorption. To clarify the mechanisms of temperature dependence of the investigated organo-clay minerals, structural properties and thermal stabilities were examined by in situ powder X-ray diffraction (XRD), thermogravimetry (TG), thermocalorimetry (DTA) and FTIR spectral analyses. The organic cations HDPy, HDTMA and BE form bilayers, pseudotrimolecular layers and paraffin-type structures. The basal spacings of DPyDD-smectite and DPyDD-vermiculite were more or less unchanged in comparison to the original clay minerals (∼1.4 nm). It is assumed that the anion adsorption is due to the uptake of organic cations in an excess of the CEC, predominantly in the interlayer spaces as ion pairs. The decreasing iodide adsorption with increasing temperature is probably due to conformational changes of the alkyl chains, which are most pronounced for DPyDD-vermiculite at 60 °C (1.48→1.20 nm). Additionally, dehydration reactions, which occur at distinct temperatures for the organo-vermiculites (HDPy, 71; HDTMA, 57, 72; BE, 61; DPyDD, 41 °C), may be another reason for a decrease in iodide adsorption. The thermal decomposition of the organic cation starts at 200 °C. The HDPy, HDTMA and DPyDD-smectites and the HDTMA and BE-vermiculites show a high thermal stability with the basal spacing remaining constant up to 150 °C, which recommends the use for anion retention in engineered barriers for heat-producing waste.

Stereoselective synthesis of optically active disilanes and selective functionalization by the cleavage of silicon-naphthyl bonds with bromine.

Optically active disilanes with one chiral silicon center, (R)-1,2-dimethyl-1-(naphth-1-yl)-1,2,2-triphenyldisilane and (R)-1,2,2-trimethyl-2-(4-methoxynaphth-1-yl)-1-(naphth-1-yl)-1-phenyldisilane, were obtained by the reaction of (S)-methyl(naphth-1-yl)phenylchlorosilane (> 99% ee) with methyldiphenylsilyllithium or by the reaction of methyldiphenylchlorosilane with optically active (S)-methyl(naphth-1-yl)phenylsilyllithium and by the reaction of (S)-methyl(naphth-1-yl)phenylchlorosilane (> 99% ee) with dimethyl(4-methoxynaphth-1-yl)silyllithium. Under the optimized conditions, the reactions proceeded with almost complete inversion for the cholorosilanes and retention for the silyl anions. Optically active disilanes with two chiral centers, (1R,2R)-1,2-dimethyl-1,2-di(naphth-1-yl)-1,2-diphenyldisilane and (1S,2S)-1,2-di(4-methoxynaphth-1-yl)-1,2-dimethyl-1,2-diphenyldisilane, were obtained in high optical purity by the reactions of corresponding optically active halogenosilanes (Cl or F) with optically active silyllithiums. The silicon-silicon bond and the silicon-naphthyl bond of (R)-1,1,2-trimethyl-1,2-di(naphth-1-yl)-2-phenyldisilane and (1R,2R)-1,2-dimethyl-1,2-di(naphth-1-yl)-1,2-diphenyldisilane were cleaved without selectivity on bromination. The silicon-(4-methoxynaphth-1-yl) bond of (R)-1,2,2-trimethyl-2-(4-methoxynaphth-1-yl)-1-(naphth-1-yl)-1-phenyldisilane was regiospecifically cleaved, followed by the stereoselective cleavage of the remaining chiral silicon-naphthyl bond (94% inversion). Although the silicon-(4-methoxynaphth-1-yl) bonds of (1S,2S)-1,2-di(4-methoxynaphth-1-yl)-1,2-dimethyl-1,2-diphenyldisilane (> 99% ee) were regioselectively cleaved without silicon-silicon bond scission, remarkable racemization could not be avoided during the one-pot reaction.

Determination of iodide in seawater and edible salt by microcolumn liquid chromatography with poly(ethylene glycol) stationary phase

An ion chromatography method for rapid and direct determination of iodide in seawater and edible salt is reported. Separation was achieved using a laboratory-made C30 packed column ( 100 mm×0.32 mm i.d.) modified with poly(ethylene glycol) (PEG). Effects of eluent composition on retention behavior of inorganic anions have been investigated. Both cation and anion of the eluent affected the retention of analyte anions. The retention time of anions increased with increasing eluent concentration when lithium chloride, sodium chloride, potassium chloride, sodium sulfate, magnesium sulfate were used as the eluent, while it decreased with increasing eluent concentration when ammonium sulfate was used as the eluent. The detection limit for iodide obtained by injecting 0.2 μl of sample was 9 μg/l (S/N = 3). The present method was successfully applied to the rapid and direct determination of iodide in seawater and edible salt samples. Partition may be involved in the present separation mode.

Ion-Chromatography Performance of Poly(Aspartic) Acid Bonded Silica with Various Pore Sizes at Different Ionic Strengths and Column Temperatures

A significant effect of pore size on selec- tivity was observed for anion exchange on polyaspartic acid-coated silica (PolyCAT A). The retention order of halogenide anions, Cl � <Br � <I � , was completely reversed between 30 nm and 6 nm pore materials. The zwitterionic nature of PolyCAT A made possible the simultaneous separation of anions and cations. With the column temperature, retention of cations is increased whereas retention of anions is decreased. The ionic composition of the eluent had a dramatic effect on separation efficiency with PolyCAT A of 30 nm pores. The separation efficiency of ions was optimal in sulfuric acid-based eluents of reasonably high ionic strength.

Impact of pre-existing sulphate on retention of imported chloride and nitrate in variable charge soil profiles

In variable charge soils, anion retention and accumulation through adsorption at exchange sites is a competitive process. The objectives of this study in the wet tropics of far north Queensland were to investigate (i) whether the pre-existing high sulphate in variable charge soils had any impact on the retention of chloride and nitrate, derived mostly from the applied fertilizer; and (ii) whether chloride competed with nitrate during the adsorption processes. Soil cores up to 12.5 m depth were taken from seven sites, representing four soil types, in the Johnstone River Catchment. Six of these sites had been under sugarcane ( Saccharum officinarum-S) cultivation for at least 50 years and one was an undisturbed rainforest. The cores were segmented at 1.0 m depth increments, and subsamples were analysed for nitrate-N, cation (CEC)- and anion-exchange capacities (AEC), pH, exchangeable cations (Ca, Mg, K, Na), soil organic C (SOC), electrical conductivity (EC), sulphate-S, and chloride. Sulphate-S load in 1–12 m depth under cropping ranged from 9.4 to 73.9 t ha −1 (mean=40 t ha −1) compared with 74.4 t ha −1 in the rainforest. Chloride load under cropping ranged from 1.5 to 9.6 t ha −1 (mean=4.9 t ha −1) compared to 0.9 t ha −1 in the rainforest, and the nitrate-N load from 113 to 2760 kg ha −1 (mean=910 kg ha −1) under cropping compared to 12 kg ha −1 in the rainforest. Regardless of the soil type, the total chloride or nitrate-N input in fertilisers was 7.5 t ha −1, during the last 50 years. Sulphate-S distribution in soil profiles decreased with depth at >2 m, whereas bulges of chloride or nitrate-N were observed at depths >2 m. This suggests that chloride or nitrate adsorption and retention increased with decreasing sulphate dominance. Abrupt decreases in equivalent fraction of sulphate (EFSO 4), at depths >2 m, were accompanied by rapid increases in equivalent fraction of chloride (EFCl), followed by nitrate (EFNO 3). The stepwise regression for EFCl and EFNO 3 indicated that nitrate retention was reduced by the pre-existing sulphate and imported chloride, whereas only sulphate reduced chloride adsorption. The results indicate that chloride and nitrate adsorption and retention occurred, in the order chloride>nitrate, in soils containing large amounts of sulphate under approximately similar total inputs of N- and Cl-fertilisers.

Demonstration of simultaneous anion-exchange and reversed-phase behavior on a strong anion-exchange column

We demonstrate in this report that a conventional silica-based strong anion-exchange column can exhibit reversed-phase chromatographic behavior simultaneously with ion-exchange in a methanol–aqueous phthalate mobile phase. Reversed-phase behavior is shown for PAHs in relatively high methanol-content mobile phases, while polar organics exhibit reversed-phase behavior in 0–10% (v/v) methanol–water eluents. At low concentrations (0–10% v/v) methanol has little or no effect on anion retention, while the anions exhibit only slight increases in retention in 60–80% (v/v) methanol at near-neutral pH values. Likewise, pH changes used to manipulate anion retention have essentially no effect on PAH retention, and cause only small decreases in retention for most of the polar organics studied. Little or no pH-effect was seen on a phenyl column (no exchange group) or with acetate mobile phase. It is shown that manipulation of pH and methanol content allows the grouping of neutral organic analytes early in a chromatogram, followed by the anions, with no class overlap. Several example chromatograms are given, including that of a red wine sample. Column efficiency was good for anions but only modest for organics.

Bromide and nitrate movement through undisturbed soil columns.

Field experiments often assume that Br-, 14NO3(-)-N, and 15NO3(-)-N have similar leaching kinetics. This study tested this assumption. Twenty-four undisturbed soil columns (15-cm diameter) were collected from summit-shoulder, backslope, and footslope positions of a no-tillage field with a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Each of the landscape positions had a different soil series. After conditioning the columns with 4 L of 0.01 M CaCl2 (2 pore volumes), 15N-labeled Ca(NO3)2 and KBr were applied to the soil surface and leached with 4 L of 0.01 M CaCl2. Leachate was collected, weighed, and analyzed for NO3(-)-N, NH4(+)-N, 15N, 14N, and Br-. The total amount of 15NO3(-)-N and 14NO3(-)-N collected in 1000, 2000, and 3000 mL of leachate was similar. These data suggest that 15N discrimination during leaching did not occur. Bromide leached faster through the columns than NO3(-)-N. The more rapid transport of Br- than NO3(-)-N was attributed to lower Br- (0.002 +/- 0.036 mg kg(-1)) than NO3(-)-N (0.17 +/- 0.03 mg kg(-1)) sorption. Results from this study suggest that (i) if Br- is used to estimate NO3(-)-N leaching loss, then NO3(-)-N leaching losses may be overestimated by 25%; (ii) the potential exists for landscape position to influence anion retention and movement in soil; and (iii) 15N discrimination was not detected during the leaching process.

Protease-activated receptor-4 uses dual prolines and an anionic retention motif for thrombin recognition and cleavage.

Thrombin activation of human platelets is mediated by the high-affinity PAR1 (protease-activated receptor-1) and the low-affinity PAR4 receptor. PAR1 and PAR4 exhibit markedly disparate kinetics of activation that likely reflect differences in the macromolecular association of thrombin with their respective N-terminal extracellular domains (exodomains). Here we examine the mechanism of initial thrombin binding and cleavage of the high- and low-affinity PAR exodomains using steady-state kinetic analyses. We showed that the PAR4 exodomain lacks the functional hirudin-like sequence found in PAR1 and does not bind exosite I to cause allosteric activation or inhibition of thrombin. Instead, PAR4 contains an anionic cluster, Asp(57)...Asp(59) ...Glu(62)...Asp(65) (DDED), in its exodomain, which slows the dissociation of PAR4 from the cationic thrombin. The analogous anionic residues in the PAR1 exodomain do not influence affinity for thrombin. Although PAR4 is cleaved more slowly than PAR1 on the cell surface, peptides containing the PAR4 P(4)-P(1) active-site-interacting sequence, Pro(45)-Ala-Pro-Arg (PAPR), are efficiently cleaved due to the optimal placement of dual prolines at positions P(4) and P(2). In comparison, thrombin has low affinity and slow cleavage rates for peptides that have a P(3) proline as occurs in human PAR3. Thus, to compensate for the lack of exosite I binding, PAR4 utilizes proline residues in its P(4)-P(1) sequence to provide high-affinity interactions with the active site and an anionic cluster to slow dissociation from the cationic thrombin.

Mechanistic studies on the separation of cations in zwitterionic ion chromatography

Electrostatic ion chromatography, also known as zwitterionic ion chromatography, has been predominantly used for the analysis of anions. Consequently, separation mechanisms proposed for this technique have been based on anion retention data obtained using a sulfobetaine-type surfactant-coated column. A comprehensive cation retention data set has been obtained on a C 18 column coated with the zwitterionic surfactant N-tetradecylphosphocholine (which has the negatively and positively charged functional groups reversed in comparison to the sulfobetaine surfactants), with mobile phases being varied systematically in the concentration and species of both the mobile-phase anion and cation. A retention mechanism based on both an ion exclusion effect and a direct (chaotropic) interaction with the inner negative charge on the zwitterion is proposed for the retention of cations. Despite the relatively low chaotropic nature of cations compared with anions, the retention data shows that cations are retained in this system predominantly due to a chaotropic interaction with the inner charge, analogous to anions in a system where the C 18 column is coated with a sulfobetaine-type surfactant. The retention of an analyte cation, and the effect of the mobile-phase anion and cation, can be predicted by the relative positions of these species on the Hofmeister (chaotropic) series.

Electrostatic ion chromatography using a carboxybetaine-type zwitterionic surfactant as the stationary phase.

A carboxybetaine-type zwitterionic stationary phase obtained by immobilizing Mitsubishi Reagent EF-700 (C(8)F(17)SO(2)NHC(3)H(6)N(+) (CH(3))(2)-C(2)H(4)-COO(-)) onto a reversed-phase column was used for chromatographic separation of ions. When aqueous electrolyte solutions having higher pH values (>8) were used as eluents, the model analyte ions (NO(2)(-), H(2)PO(4)(-), Cl(-), Br(-), NO(3)(-), ClO(3)(-), I(-) and SCN(-)) were co-eluted and appeared at the void volume of this HPLC system. However, when aqueous electrolyte solutions having lower pH values (<5.5) were used as eluents, these anions were well retained and separated. Furthermore, when acetate buffers (NaAc/HAc) were used as eluents, plots of log k' (k', retention factor) versus pH of eluents (at constant [NaAc+HAc]), and log k' versus log [NaAc+HAc] (at constant pH), were linear with negative slopes. Breakthrough curves for acid solutions obtained using conductivity detection showed that H(+) ions and their conjugate anions were both retained on the stationary phase and the degree of binding was found to be independent of the acid species used. The degree to which the eluent cation was bound onto the carboxylate functionality of the zwitterion was found to exert a major effect on the retention of analyte anions. A strongly bound cation, such as H(+), reduced electrostatic repulsion effects exerted by the carboxylate functionality on analyte anions, so that they could freely access the quaternary ammonium sites on the zwitterion. It is concluded based on these experimental results that both the charges on the zwitterionic stationary phase make meaningful contributions to the separation of the analyte ions.

Retention of anions on silica-based metalloporphyrin stationary phases.

The silica-based Fe(III)-protoporphyrin and Zn-tetraphenylporphyrin stationary phases were examined for the HPLC separation of anions. The retention of nine common inorganic anions as well as benzoate anion (BA) and its hydroxy analogues (HBA) was examined using tartrate, acetate, and succinate eluents. The retention factors of inorganic anions on the FeProP stationary phase were in the order Cl- < NO3- < ClO4- < I- < SCN- and for organic anions benzoate < p-hydroxybenzoate < m-hydoxybenzoate < o-hydroxybenzoate. The retention factors of organic anions examined for a ZnTPP column were in the order p-HBA < m-HBA < BA < o-HBA.

PHOSPHATE AND SULFATE RETENTION BY NONVOLCANIC SOILS WITH ANDIC PROPERTIES

Soils with andic properties have a high anion retention capacity, which is mainly related to the large amounts of active Al and Fe compounds that they contain. The phosphate (PO 4 ) and sulfate (SO 4 ) sorption capacity of soils with andic properties from Galicia, NW Spain, was investigated. Phosphate sorption experiments were conducted by adding 1.6, 16.1, and 48 mM KH 2 PO 4 to soils, and those of sulfate by adding 0.4 and 1.6 mM K 2 SO 4 (ratio of soil:solution, 1:10). The pH of the extracts was measured, as were the levels of PO 4 (only in the PO 4 experiments), SO 4 , Si, and dissolved organic carbon. The soils retained much higher amounts of PO 4 than of SO 4 . Surface horizons displayed a higher capacity than subsurface horizons for retaining PO 4 but not for retaining SO 4 . The PO 4 retention capacity was related to the sum of contents of oxalate extractable-Al (Al o ) and -Fe (Fe o ), which tended to increase with soil organic carbon content and was mainly attributed to the presence of Al-humus complexes. Sorption of PO 4 primarily produced displacement of dissolved organic carbon, Si, and SO 4 into solution and increases in solution pH, whereas sorption of SO 4 only generated increases in solution pH. The low ability of SO 4 anions to displace sorbed organic C mainly explains why surface horizons retained similar or even smaller amounts of SO4 than subsurface horizons, despite the higher Al o and Fe o contents of the former. The results emphasize the different affinities of PO 4 and SO 4 for reactive surfaces and the interaction of organic C in sorption processes.

Effect of temperature on retention and selectivity in ion chromatography of anions

The temperature dependence of retention of a wide range of inorganic anions is studied on two commercially available ion exchangers (Dionex AS11 and AS14 columns). Anion retention exhibited both exothermic and endothermic behavior, such that varying the temperature from ambient to 60°C produced selectivity changes. The anions displayed three groupings of temperature dependence: weakly retained singly charged anions (e.g., iodate, bromate, nitrite, bromide and nitrate); multiply charged anions (sulfate, oxalate, phosphate and thiosulfate); and strongly retained singly charged anions (iodide, thiocyanate and perchlorate). Temperature was ineffective at changing the selectivity of retention between anions of the same grouping. However, significant selectivity changes, including elution order reversal, could be achieved between anions from different groupings.