Influence of anions on the adsorption kinetics of salicylate onto alpha-alumina in aqueous medium

The adsorption kinetics of salicylate on alpha-alumina surfaces were studied at 25 degrees C and pH 6 in the presence of 0.05 mM concentration of different anions (Cl(-), Br(-), I(-), SCN(-), HCOO(-), CH(3)COO(-), S(2)O(2-)(3), CO(2-)(3), and SO(2-)(4)) as a function of time. The experimental data were significantly better fitted to a pseudo-second-order kinetics equation of nonlinear form in the entire time duration and are in excellent agreement with corresponding estimated values. Considering adsorption data for salicylate in the presence of Cl(-) as the face value, all the monovalent anions (Br(-), I(-), SCN(-), HCOO(-), CH(3)COO(-)) promote the adsorption of salicylate onto alpha-alumina surfaces while the divalent anions (S(2)O(2-)(3), CO(2-)(3), and SO(2-)(4)) have the reverse effect under similar conditions. DRIFT spectra of alpha-alumina treated with salicylate reveal that the symmetric peak nu(s)(COO(-)) is shifted by approximately 40 cm(-1) to a lower wavelength region, which implies that salicylate forms an inner-sphere complex with alpha-alumina surface in the presence of both mono- and divalent anions.     

Hofmeister effects on electron-transfer reactions of 1-pyrenesulfonic acid radical cation with nucleophilic anions in Nafion membranes

The electron-transfer reaction from nucleophilic anions such as SCN(-), N(3)(-), I(-), and Br(-) to the 1-pyrenesulfonic acid radical cation (Py(*+)SA(-)) generated via a resonant two-photon ionization process in the Nafion membranes was investigated with transient absorption measurements. The apparent quenching rates observed in the Nafion membrane (k(q)(Nf)) were almost 2-4 orders smaller than those observed in the bulk solutions (k(q)(bulk)). The attenuation factor (AF), which is defined as log(k(q)(Nf)/k(q)(bulk)), decreased in the order SCN(-) > N(3)(-) > I(-) > Br(-). This interesting behavior was interpreted in terms of the anionic Hofmeister effects. The effects of hydrophobic organic cations such as tetrabutylammonium ion (Bu(4)N(+)) and tetraethylammonium ion (Et(4)N(+)) exchanged into the Nafion membranes were also examined.     

Modification by fluoride,bromide, iodide,thiocyanate and nitrite anions of reaction of a myeloperoxidase-H2O2-Cl- system with nucleosides

The influence of fluoride (F(-)), bromide (Br(-)), iodide (I(-)), thiocyanate (SCN(-)) and nitrite (NO(2)(-)) on the reaction of a myeloperoxidase-H(2)O(2)-Cl(-) system with a nucleoside mixture was studied. The reaction was carried out under mildly acidic conditions and terminated by N-acetylcysteine. Without the additional anions, quantity of nucleosides consumed fell in the following order: 2'-deoxyguanosine>2'-deoxycytidine>2'-deoxythymidine>2'-deoxyadenosine asymptotically equal to 0. F(-) did not affect the reaction. Br(-) increased the consumption of 2'-deoxycytidine and 2'-deoxythymidine, but decreased that of 2'-deoxyguanosine. I(-), SCN(-) and NO(2)(-) suppressed the reaction. These results suggest that Br(-) has a unique effect in relation to nucleoside damage caused by myeloperoxidase.     

p-tert-Butyl thiacalix[4]arenes functionalized at the lower rim by amide, hydroxyl and ester groups as anion receptors

New p-tert-butyl thiacalix[4]arenes differently substituted at the lower rim with amide, hydroxyl and ester groups were synthesized. Binding properties of the compounds toward some tetrabutylammonium salts n-Bu(4)NX (X = F(-), Cl(-), Br(-), I(-), CH(3)CO(2)(-), H(2)PO(4)(-), NO(3)(-)) were studied by UV spectroscopy. It was found that the stoichiometry of the complexes, generally, is 1 : 1, and the association constants are in the range of 10(3)-10(5) M(-1). The p-tert-butyl thiacalix[4]arenes containing secondary amide groups trisubstituted at the lower rim bind the studied anions most effectively. Selective receptors for fluoride and dihydrogen phosphate salts of tetrabutylammonium were found.     

Tuning metal@metal salt photocatalytic abilities by different charged anions

A series of high performance Ag@Ag salts photocatalysts were designed and fabricated. The photocatalytic abilities of this kind of catalysts can be tuned by altering the negative charged ions (Cl(-), Br(-), I(-), CrO(4)(2-), PO(4)(3-), PW(12)O(40)(3-), and SiW(12)O(40)(4-)): higher stability and higher charged anions lead to the stronger photocatalytic ability.     

Anion exchange reaction potentials as approximate estimates of the relative thermodynamic stabilities of Mg/Al layered double hydroxides containing different anions

Coatings of hydrotalcite-like nitrate-intercalated Mg/Al layered double hydroxides are electrochemically deposited on a Pt electrode by electrogeneration of base by reduction of a mixed metal nitrate aqueous solution. As-prepared coatings are stable to workup and function as rugged electrodes. The voltammetric response generated by anion exchange of intercalated nitrate for dissolved anions from solution under equilibrium conditions is employed to estimate the thermodynamic stabilities of the Mg/Al layered double hydroxides comprising different anions relative to the nitrate-containing phase. Among monovalent anions, the most stable is the fluoride-containing LDH (ΔG° = -48.7 kJ mol(-1)) relative to the nitrate-containing LDH. The stability in aqueous phase decreases as F(-) > Cl(-) > Br(-) > NO(2)(-) > NO(3)(-), whereas, among divalent anions, SO(4)(2-) (ΔG° = -8.7 kJ mol(-1)) > CO(3)(2-) (ΔG° = 14.3 kJ mol(-1)). The results of monovalent ions match well with the Miyata series, whereas the divalent anion series is at variance with the commonly held belief that carbonate-LDHs are more stable than sulfate-LDHs.     

Long-chain alkylimidazolium ionic liquids, a new class of cationic surfactants coated on ODS columns for anion-exchange chromatography

Separations of common inorganic anions were carried out on ODS columns coated with two long-chain alkylimidazolium ionic liquids ([C(12)MIm]Br and [C(14)MIm]Br) as new cationic surfactants for ion chromatography. With phthalate buffer solution as the mobile phases and non-suppressed conductivity detection, high column efficiencies and excellent selectivity were obtained in the separation of inorganic anions. Chromatographic parameters are calculated and the results show that the coated column possesses significant potential for the analysis of some inorganic anions such as CH(3)COO(-), IO(3)(-), Cl(-), BrO(3)(-), NO(2)(-), Br(-), NO(3)(-), SO(4)(2-), I(-), BF(4)(-), and SCN(-). The effect of eluent pH values on the separation of anions has been studied on the column coated with [C(12)MIm]Br. The stability of the coated columns was also examined.     

From simple to complex: topological evolution and luminescence variation in a copper(I) pyridylpyrazolate system tuned via second ligating spacers

By systematically varying the geometric length and electronic properties of the second ligating ligands of halogen (Cl(-), Br(-), and I(-)) and pseudohalogen (CN(-), SCN(-), and N(3)(-)) anions, we synthesized 11 isomeric/isostructural copper(I) complexes: [Cu(2)(L3-3)I](n) (1), [Cu(2)(L4-4)Br](n) (2-Br), [Cu(2)(L4-4)Cl](n) (2-Cl), [Cu(2)(L3-4)(CN)](n) (3), [Cu(2)(L3-3)(CN)](n) (4), [Cu(3)(L4-4)(CN)(2)](n) (5), {[Cu(2)(L4-4)Br](2)·CuBr}(n) (6-Br), {[Cu(2)(L4-4)Cl](2)·CuCl}(n) (6-Cl), [Cu(2)(L4-4)(SCN)](n) (7α-SCN), [Cu(2)(L4-4)(SCN)](n) (7β-SCN), and [Cu(2)(L4-4)(N(3))](n) (7α-N(3)). These structures are based on a series of isomeric pyridylpyrazole ligands, namely, 3,5-bis(3-pyridyl)-1H-pyrazole (HL3-3), 3-(3-pyridyl)-5-(4-pyridyl)-1H-pyrazole (HL3-4), and 3,5-bis(4-pyridyl)-1H-pyrazole (HL4-4), and their structural features range from 1-D (1), 2-D (2), and 3-D noninterpenetration (3), to 3-D 2-fold interpenetration (4 and 5), to 3-D self-catenation (6 and 7), exhibiting a trend from simple to complex with dimension expansion and an interpenetrating degree increase. The five most complex structures (6 and 7) with self-catenated networks are based on 2-fold interpenetrated networks linked via appropriate second ligating spacers (Cl(-), Br(-), SCN(-), and N(3)(-)), representing a strategy to construct self-catenated coordination polymers through cross-linking interpenetrated frameworks. Moreover, these complexes exhibit strong photoluminescence, which is mainly ascribed to Cu(I)-related charge transfers (MLCT, MC, and MMLCT) regulated by the electronic properties of halogen or pseudohalogen. The topological evolution and luminescence variation presented in this work open an avenue to understanding the luminescence origin and the structure-property relationship of luminescent coordination polymers.     

Anion binding to a ferric porphyrin complexed with per-O-methylated beta-cyclodextrin in aqueous solution

5,10,15,20-Tetrakis(4-sulfonatophenyl)porphinato iron(III) (Fe(III)TPPS) forms a very stable 1:2 complex with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMe-beta-CD), whose iron(III) center is located at a hydrophobic cleft formed by two face-to-face TMe-beta-CD molecules. Various inorganic anions (X(-)) such as F(-), Cl(-), Br(-), I(-), N(3)(-), and SCN(-) coordinate to Fe(III)TPPS(TMe-beta-CD)(2) to form five-coordinate high-spin Fe(III)TPPS(X)(TMe-beta-CD)(2), while no coordination occurs with ClO(4)(-), H(2)PO(4)(-), NO(3)(-), and HSO(4)(-). Except for F(-), none of the anions investigated coordinate to Fe(III)TPPS in the absence of TMe-beta-CD due to extensive hydration to the anions as well as to Fe(III)TPPS. The present system shows a high selectivity toward the N(3)(-) anion. The thermodynamics suggests that Lewis basicity, hydrophilicity, and shape of an X(-) anion are the main factors to determine the stability of the Fe(III)TPPS(X)(TMe-beta-CD)(2) complex.     

Enhanced selectivity and sensitivity for inorganic anions using an ion-pairing reagent and sample stacking in capillary zone electrophoresis with direct UV detection

In this paper, the use of an ion-pairing reagent to improve the separation selectivity of inorganic anions in CZE was demonstrated by the addition of tetramethylammonium hydroxide (TMAOH) to the electrolyte. The separation of inorganic anions (Cl(-), I(-), Br(-), NO(2)(-), NO(3)(-) and SCN(-)) was performed using co-electroosmotic flow (EOF) with direct UV detection at 185 nm. The parameters affecting the mobility of the tested anions and the EOF such as the electrolyte pH and concentration of TMAOH in the electrolyte were examined to optimise the separation conditions. In addition, sample-stacking techniques were investigated to improve detection sensitivity. Detection sensitivities were improved 5-13-fold using electrokinetic sample stacking. The detection limits ranged from 1-3 micro mol L(-1). Finally, the proposed method was used for the separation of anions in groundwaters.     

CO在超临界水中的转化以及碱性钾盐的影响

构建了CO高压溶解的进气系统,在连续式反应系统中对超临界水条件下CO的转化规律进行了研究;针对生物质超临界水气化中钾盐的多样性,选择KHCO₃、K₂CO₃和KOH等三种钾盐成分,研究了它们在不同工艺条件（450-600℃、23-29 MPa、停留时间3-6 s）下对超临界水中水煤气转化过程的影响。结果表明,在无催化条件下,提高反应温度、延长停留时间均提高了CO的转化率,而压力对其影响在低压下（23-25 MPa）比较大,高压下（25-29 MPa）比较小,水煤气转化的反应动力学方程为k=10^3.75×exp（-0.66×10⁵/RT）（s^-1）。碱性钾盐均能显著提高CO转化率,其催化促进程度从大到小依次为：KHCO₃>K₂CO₃>KOH。添加碱性钾盐时,提高反应温度、延长停留时间均提高CO转化率,而压力的影响比较复杂。碱性盐对水煤气转化反应的催化是通过草酸盐（HC₂O₄^-）和甲酸盐（HCOO^-）作为中间产物进行的。     

Reversed-phase liquid chromatography of alkaloids: Masking effects of inorganic salts

The addition of salts (investigated cations Na(+), NH(+)(4), K(+), KBu(+)(4) combined with the anions acetate, Br(-), SCN(-) and I(-)) can be used to eliminate peak tailing and to decrease retention of cationic species in the course of the separation of alkaloids from Chelidonium majus L. by reversed-phase chromatography on a ODS Hypersil column, using water-acetonitrile-methanol mixture as eluent. These findings are interpreted in terms of a silanol masking effect. The extended donor-acceptor concept is used to interpret the effectiveness of different salts in masking the active sites of the stationary phase.     

Triphenylene based copper ensemble for the detection of cyanide ions

The binding behavior of triphenylene based copper ensemble prepared in situ has been investigated toward various anions (F(-), Cl(-), Br(-), I(-), CH(3)COO(-), H(2)PO(4)(-), NO(3)(-), OH(-), ClO(4)(-), CN(-), CO(3)(-) and SO(4)(-)) by UV-vis and fluorescence spectroscopy. Among various anions tested, 1-Cu(2+) ensemble shows selective and sensitive response towards cyanide ions and responds to CN(-) ions even in the presence of bovine serum albumin and in blood serum milieu. Further, as practical application of compound 1, we utilized the TLC strips coated with THF solution of 1 for the solid state detection of copper and cyanide ions.     

Electron photodetachment from aqueous anions. 3. Dynamics of Geminate pairs derived from photoexcitation of mono- vs polyatomic anions

Photostimulated electron detachment from aqueous inorganic anions is the simplest example of solvent-mediated electron transfer reaction. As such, this photoreaction became the subject of many ultrafast studies. Most of these studied focused on the behavior of halide anions, in particular, iodide, that is readily accessible in the UV. In this study, we contrast the behavior of these halide anions with that of small polyatomic anions, such as pseudohalide anions (e.g., HS(-)) and common polyvalent anions (e.g., SO(3)(2-)). Geminate recombination dynamics of hydrated electrons generated by 200 nm photoexcitation of aqueous anions (I(-), Br(-), OH(-), HS(-), CNS(-), CO(3)(2-), SO(3)(2-), and Fe(CN)(6)(4-)) have been studied. Prompt quantum yields for the formation of solvated, thermalized electrons and quantum yields for free electrons were determined. Pump-probe kinetics for 200 nm photoexcitation were compared with kinetics obtained at lower photoexcitation energy (225 or 242 nm) for the same anions, where possible. Free diffusion and mean force potential models of geminate recombination dynamics were used to analyze these kinetics. These analyses suggest that for polyatomic anions (including all polyvalent anions studied) the initial electron distribution has a broad component, even at relatively low photoexcitation energy. There seems to be no well-defined threshold energy below which the broadening of this electron distribution does not occur, as is the case for halide anions. The constancy of (near-unity) prompt quantum yields vs the excitation energy as the latter is scanned across the lowest charge-transfer-to-solvent band of the anion is observed for halide anions but not for other anions: the prompt quantum yields are considerably less than unity and depend strongly on the excitation energy. Our study suggests that halide anions are in the class of their own; electron photodetachment from polyatomic, especially polyvalent, anions exhibits qualitatively different behavior.     

Fluoride-selective colorimetric sensor based on thiourea binding site and anthraquinone reporter

A structurally simple colorimetric sensor, N-4-nitrobenzene-N'-1'-anthraquinone-thiourea (1), for anions was synthesized and characterized by (1)H NMR, ESI mass and IR methods. In acetonitrile, the addition of F(-) changed 1 solution from colorless to yellow. In the presence of other anions such as CH(3)CO(2)(-), H(2)PO(4)(-), HSO(4)(-) and Cl(-), however, the absorption spectrum of 1 was slightly red shifted with no obvious color changes observed. The association constants of anionic complexes followed the order of F(-)>CH(3)CO(2)(-)>H(2)PO(4)(-)>HSO(4)(-)>Cl(-)>Br(-), which was different from the order of anion basicity. AM1 calculation results indicated that the most stable configuration of 1 existed in the Z-E-conformation with a six-membered ring via intramolecular hydrogen bond. This made thiourea moiety of 1 in an unfavorable conformation to bond with oxygen-anionic substrates such as CH(3)CO(2)(-) and H(2)PO(4)(-), thus leading to a high selectivity and sensitivity for the detection of F(-).     

Fluorene-based Cu(II)-MOF: a visual colorimetric anion sensor and separator based on an anion-exchange approach

A new 2D Cu(II)-MOF generated from a fluorene-based ligand and Cu(NO(3))(2) was reported. It is an interesting visual colorimetric anion sensor. In addition, it can completely separate Cl(-)/Br(-), Br(-)/I(-) and SCN(-)/N(3)(-) anions under ambient conditions.     

Hyperbranched polymers with thermoresponsive property highly sensitive to ions

The salt effects on the water solubility of thermoresponsive hyperbranched polyethylenimine and polyamidoamine possessing large amounts of isobutyramide terminal groups (HPEI-IBAm and HPAMAM-IBAm) were studied systematically. Eight anions with sodium as the counterion and ten cations with chloride as the counterion were used to measure the anion and cation effects on the cloud point temperature (T(cp)) of these dendritic polymers in water. It was found that the T(cp) of these dendritic polymers was much more sensitive to the addition of salts than that of the traditional thermoresponsive linear polymers. At low anion concentration, the electrostatic interaction between anions and the positively charged groups of these polymers was dominant, resulting in the unusual anion effect on the T(cp) of these polymers in water, including (1) T(cp) of these dendritic polymers decreasing nonlinearly with the increase of kosmotropic anion concentration; (2) the chaotropic anions showing abnormal salting-out property at low salt concentration and the stronger chaotropes having much pronounced salting-out ability; (3) anti-Hofmeister ordering at low salt concentration. At moderate to high salt concentration, the specific ranking of these anions in reducing the T(cp) of HPEI-IBAm and HPAMAM-IBAm polymers was PO(4)(3-) > CO(3)(2-) > SO(4)(2-) > S(2)O(3)(2-) > F(-) > Cl(-) > Br(-) > I(-), in accordance with the well-known Hofmeister series. At moderate to high salt concentration, the specific ranking order of inorganic cations in reducing the T(cp) of HPEI-IBAm polymer was Sr(2+) ≈ Ba(2+) > Na(+) ≈ K(+) ≈ Rb(+) > Cs(+) > NH(4)(+) ≈ Ca(2+) > Li(+) ≈ Mg(2+). This sequence was only partially similar to the typical Hofmeister cation series, whereas at low salt concentration the cation effect on T(cp) of the dendritic polymer was insignificant and no obvious specific ranking order could be found.     

Specific ion effects on the electrochemical properties of cytochrome c

The range of salts used as supporting electrolytes in electrochemical studies of redox proteins and enzymes varies widely, with the choice of an electrolyte relying on the assumption that the electrolyte used does not affect the electrochemical properties of the proteins and enzymes under investigation. Examination of the electrochemical properties of the redox protein cytochrome c (cyt c) at a 4,4'-bipyridyl modified gold electrode demonstrates that both the redox potential (E(o')) and the faradaic current are influenced by the nature of the electrolyte used, in a manner explained primarily by Hofmeister effects. The faradaic peak currents display an atypical trend on switching from kosmotropic to chaotropic anions, with a maximum current observed in the presence of Cl(-). For a series of cations, the peak current increased in the sequence: Li(+) (0.34 μA) < guanidinium(+) (0.36 μA) < Na(+) (0.37 μA) < K(+) (0.38 μA) < Cs(+) (0.40 μA) and for anions it decreased in the sequence: Cl(-) (0.37 μA) > Br(-) (0.35 μA) > ClO(4)(-) (0.35 μA) > SCN(-) (0.31 μA) > F(-) (0.30 μA). E(o') decreased by a total of 24 mV across the series F(-) > Cl(-) > Br(-) > ClO(4)(-) > SCN(-) whereas no specific ion effect on E(o') was observed for cations. Factorisation of E(o') into its enthalpic and entropic components showed that while no specific trends were observed, large changes in ΔH(o') and ΔS(o') occurred with individual ions. The effect of anions on the faradaic peak current can be qualitatively explained by considering Collins' empirical rule of 'matching water affinities'. The effect of cations cannot be explained by this rule. However, both anion and cation effects can be understood by taking into account the cooperative action of electrostatic and ion dispersion forces. The results demonstrate that the choice of a supporting electrolyte in electrochemical investigations of redox proteins is important and emphasize that care needs to be taken in the determination and comparison of E(o'), ΔH(o') and ΔS(o') in different solutions.     

Synthesis and characterization of cobalt(II) complexes with tripodal polypyridine ligand bearing pivalamide groups. Selective formation of six- and seven-coordinate cobalt(II) complexes

The reactions of CoX(2) (X = Cl(-), Br(-), I(-) and ClO(4)(-)) with the tripodal polypyridine N(4)O(2)-type ligand bearing pivalamide groups, bis(6-(pivalamide-2-pyridyl)methyl)(2-pyridylmethyl)amine ligand (H(2)BPPA), afforded two types of Co(II) complexes as follows. One type is purple-coloured Co(II) complexes, [CoCl(2)(H(2)BPPA)] (1(Cl)) and [CoBr(2)(H(2)BPPA)] (1(Br)) which were prepared when X = Cl(-) and Br(-), respectively. The other type is pale pink-coloured Co(II) complexes, [Co(MeOH)(H(2)BPPA)](ClO(4)(-))(2) (2·(ClO(4)(-))(2)) and [Co(MeCN)(H(2)BPPA)](I(-))(2) (2·(I(-))(2)), which were obtained when X = I(-) and ClO(4)(-), respectively. From the reaction of 1(Cl) and NaN(3), a purple-coloured complex, [Co(N(3))(2)(H(2)BPPA)] (1(azide)), was obtained. These Co(II) complexes were characterized by X-ray structural analysis, IR and reflectance spectroscopies, and magnetic susceptibility measurements. All these Co(II) complexes were shown to be in a d(7) high-spin state based on magnetic susceptibility measurements. The former Co(II) complexes revealed a six-coordinate octahedron with one amine nitrogen, three pyridyl nitrogens, and two counter anions, and one coordinated anion, Cl(-), Br(-) and N(3)(-), forming intramolecular hydrogen bonds with two pivalamide N-H groups. On the other hand, the latter Co(II) complexes showed a seven-coordinate face-capped octahedron with one amine nitrogen, three pyridyl nitrogens, two pivalamide carbonyl oxygens and MeCN or MeOH. In these structures, intramolecular hydrogen bonding interaction was not observed, and the metal ion was coordinated by the pivalamide carbonyl oxygens and solvent molecule instead of the counter anions. The difference in coordination geometries might be attributable to the coordination ability and ionic radii of the counteranions; smaller strongly binding anions such as Cl(-), Br(-) and N(3)(-) gave the former complexes, whereas bulky weakly binding anions such as I(-) and ClO(4)(-) afforded the latter ones. In order to demonstrate this hypothesis, the small stronger coordinating ligand, azide, was added to complexes 2·(ClO(4)(-))(2) to obtain the dinuclear cobalt(II) complex in which two six-coordinate octahedral cobalt(II) species were bridged with azide, 3·(ClO(4)(-)). Also, the abstraction reaction of halogen anions from complexes 1(Cl) by AgSbF(6) gave a pale pink Co(II) complex assignable to 2·(SbF(6)(-))(2).     

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.