Retention Behavior Of Inorganic Anions Research Articles

Rapid determination of chromium species in environmental waters using a diol-bonded polymer-stationary column under water-rich conditions coupled with ICPMS.

Chromium speciation analysis in environmental water is of great significance for the monitoring of water pollution and assessing its influences on human health. This study proposes a rapid analytical approach for the simultaneous determination of Cr(VI) and Cr(III) in environmental waters by hydrophilic interaction chromatography (HILIC) coupled with ICPMS under a water-rich condition. 2,6-Pyridinedicarboxylic acid (PDCA) was used to unify Cr(III) species in various chemical forms into a stable Cr(III)-PDCA anion complex and then separated from Cr(VI) oxyanion on a diol-bonded polymer-based HILIC column. An aqueous mobile phase containing 50mmol L-1 ammonium acetate (pH 7.0), 2mmol L-1 PDCA, and 4% acetonitrile successfully separates chromium species as well as chloride ions. In addition, our method elutes Cr(VI) preferentially over Cr(III)-PDCA, enabling rapid determination of Cr(VI), and both chromium species were analyzed within 6.2min. The detection limits of 0.19μg L-1 for Cr(VI) and 0.35μg L-1 for Cr(III) at m/z 52 under He collision mode are comparable to or better than the conventional ion exchange chromatography-ICPMS methods, and quantitative recovery was obtained from spike-recovery tests on river water samples containing various levels of matrix. Optimization experiments of the HPLC conditions indicate that the retentions of Cr(VI) and Cr(III)-PDCA are characterized by electrostatic and nonpolar interactions, respectively. The retention behavior of inorganic anions and cations in water-rich conditions observed in this study will provide new insights into the separation mechanism in polymer-based HILIC columns, which has been poorly understood.

Retention Behavior of Inorganic Anions in Hydrophilic Interaction Chromatography.

The retention behavior of inorganic anions was studied in hydrophilic interaction chromatography (HILIC). In this study, five kinds of HILIC stationary phases (amino, imidazole, amide, pyridine and zwitterionic) were investigated. It was found that only amino and imidazole columns exhibited the separation of inorganic anions under HILIC conditions. The retention mechanism was further investigated under both columns. A reversed elution order of inorganic anions was observed under the HILIC condition compared with those observed under the ion-exchange chromatography mode (IEC). The effect of salt species and their concentration in the eluent were investigated under constant acetonitrile (ACN) content. Sodium chloride and sodium perchlorate were chosen as the salt, and the salt (sodium perchlorate) concentration was varied from 10 to 40 mM to confirm the effect of the electrostatic interaction. The slope values of the plots of the log retention factor (k) versus the log eluent concentration were calculated to be between -0.43 and -0.45 for the amino column, while those obtained on the imidazole column were between -0.68 and -0.73. Various concentrations of ACN were also examined with 20 mM sodium perchlorate, and the typical HILIC retention behavior was observed on both amino and imidazole columns. Due to the obtained results, it is considered that the separation of inorganic anions under the HILIC condition was achieved by both electrostatic interaction and partition.

Capillary Ion Chromatography Using 18-Crown-6 Ether as Eluent Additive for the Separation of Anions

The retention behavior of inorganic anions was investigated on a hydrophobic stationary phase dynamically modified with 18-crown-6 ether (18C6) in capillary ion chromatography. Styrene–divinylbenzene copolymeric (polystyrene) packing material was used as the hydrophobic stationary phase to retain 18C6. The eluent contained 18C6, salt and acetonitrile; 18C6 was retained on the stationary phase and the analytes anions were separated by the cations, which were trapped on the 18C6 and worked as the anion-exchange sites. The effect of eluent conditions, such as eluent cation species, acetonitrile (ACN), 18C6, and salt concentrations (in this case, potassium chloride was used), was investigated. The retention times of inorganic anions decreased with increasing concentration of ACN. In case ACN concentration was less than 4%, the retention times decreased with the passage of time. The retention time of inorganic anions increased with increasing concentrations of 18C6 and potassium chloride concentrations. By contrast, high concentration of 18C6 and chloride in eluent promotes elution of inorganic anions, and the retention time decreased. Furthermore, a contactless conductivity detector was used to replace the conventional UV detector to obtain higher sensitivity detection. Separation of inorganic anions was achieved with the eluent containing potassium hydroxide and enhanced peak intensity was observed using a suppressed contactless conductivity detection.

Determination of Iodide in Seawater by Capillary Ion Chromatography Using Hexadimethrine Bromide Modified C30 Stationary Phases

A novel and simple capillary ion chromatographic method for the determination of iodide is reported. Separation was achieved on a laboratory-made packed capillary column (100 mm × 0.32 mm i.d.) packed with triacontyl-functionalized silica, followed by a modification with hexadimethrine bromide, where 1 mM sodium chloride-acetonitrile (95:5, v/v) was used as the eluent and UV-absorbing analyte anions were detected at 225 nm. The effects of the eluent composition on the retention behavior of inorganic anions were investigated. The addition of a small amount of an organic substance in an eluent such as acetonitrile increased the retention of iodide, while the addition of methanol decreased its retention. The present analytical method was successfully applied to the rapid and direct determination of iodide in seawater without any preconcentration. Also, this modified column could be used for about two months (6 h operation per day) without hexadimethrine bromide being contained in the eluent.

Separation of inorganic anions on a triazole‐functionalized ion exchanger in ion chromatography

The retention behavior of inorganic anions on a triazole-based stationary phase was first examined in ion chromatography. It was initially designed for hydrophilic interaction liquid chromatography and was simply prepared by introducing the triazole groups onto the surface of silica gel via click chemistry. Effective separation of common inorganic anions, including iodate, chloride, bromide, nitrate and iodide, was achieved with Na(2)SO(4) eluent. The logarithm of the retention factor of analytes was observed to be linear with the logarithm of the eluent concentration, and the slopes of the plots were almost the same as those of the ideal theoretical value. The eluent pH value in the range of 3.4-7.0 had little effect on the separation. The utility of the column was demonstrated for the determination of UV-absorbing anions in saliva and tap water.

Vitamin U-bonded Stationary Phase in Capillary Ion Chromatography

A vitamin U-bonded stationary phase was prepared and the retention behavior of inorganic anions was examined using ion chromatography. Inorganic anions were retained on the vitamin U-bonded stationary phase under acidic as well as neutral eluent conditions in the ion-exchange mode. The elution order of the examined anions under neutral eluent conditions was nearly the same as that observed in common ion exchange mode, while the elution order observed under acidic eluent conditions was completely different from that observed in common ion exchange mode. The retention of the analyte anions under the neutral eluent conditions was due to the sulfonium groups of the vitamin U, while protonated primary amino groups caused retention of the analyte anions with different selectivity under acidic conditions. The retention factor of the analyte anions increased with decreasing eluent concentration under both eluent conditions. The present system was applied to the determination of bromide and nitrate contained in seawater.

Separation of Inorganic Anions on a Pyridine Stationary Phase in Ion Chromatography

The retention behavior of inorganic anions on a pyridine stationary phase commercially available for hydrophilic interaction chromatography was examined in ion chromatography. Inorganic anions were retained on a protonated pyridine stationary phase under acidic eluent conditions (pH 3.1-3.3) in the ion-exchange mode. The logarithm of the retention factor of analytes was linear to the logarithm of the eluent concentration, and the slopes of the plots were -0.55 to -0.64, except for nitrite (-0.39). The smaller slope for nitrite was due to the fact that nitrous acid is weak (pK(a) 3.25 at 25 degrees C) and was partially ionized under the operating conditions. The elution order of the examined anions was the same as that observed in common ion chromatography. The present system was applied to the determination of UV-absorbing anions contained in saliva.

Poly(ethylene oxide)-bonded stationary phase for capillary ion chromatography

Methyl-capped poly(ethylene oxide) moieties were chemically bonded to silica gel using an amine-reactive modification reagent and evaluated as the stationary phase for ion chromatography. In this work, primary amino groups of an aminopropylsilica packing material were reacted with methyl-PEO(12)-NHS ester (succinimidyl-{[N-methyl]-dodecaethyleneglycol} ester) in phosphate buffer (pH 7.0) at room temperature. The prepared poly(ethylene oxide)-bonded stationary was evaluated for the separation of inorganic anions, and the retention behavior of inorganic anions on the prepared stationary phase was examined. The elution order of the investigated anions was the same as that observed in common ion chromatography. Both cations and anions of the eluent affected the retention of the analyte anions. Ion exchange was involved for the retention of analyte anions, although the present stationary phase does not possess any discrete ion-exchange sites. The stationary phase was applied to the separation of trace anions contained in tap water and a rock salt.

Determination of iodide in seawater using C30 column modified with polyoxyethylene oleyl ether in ion chromatography

An ion chromatographic method for rapid and direct determination of iodide in seawater samples is reported. Separation was achieved using a laboratory-made C30 packed column (100 mm × 0.32 mm i.d.) modified with polyoxyethylene oleyl ether, with an aqueous solution of 300 mM sodium chloride as eluent and using UV detection at 220 nm. Samples containing iodate, nitrate, iodide and thiocyanate were eluted within 8 min, and the relative standard deviations of the retention time, peak area and peak height were all smaller than 4.19% for all of the analyte anions. Effects of eluent composition on retention behavior of inorganic anions have been investigated. Both cation and anion of the eluent affected the retention time of analytes. When inorganic eluents, such as ammonium chloride, ammonium sulfate, lithium chloride, sodium chloride, sodium sulfate, magnesium chloride and magnesium sulfate were used, the retention time of analytes increased with increasing eluent concentration. The limit of detection of iodide was 19 μg l −1 (S/N = 3), while the limit of quantitation was 66 μg l −1 (S/N = 10). The present method was successfully applied to the rapid and direct determination of iodide in seawater samples.

Determination of iodide in seawater samples by ion chromatography with chemically-bonded poly(ethylene glycol) stationary phase

An ion chromatographic method for the rapid and direct determination of iodide in seawater is reported. Poly(ethylene glycol) (PEG) groups were chemically bonded onto silica gel or C30-bonded silica gel via diol groups. PEG-bonded C30 binary phases allowed determination of iodide in seawater samples without any interference. 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. The detection limit for iodide obtained by injecting 0.2 μl of sample was 13 μg l −1 (S/N = 3) while the limit of quantitation was 43 μg l −1 (S/N = 10). The present method was successfully applied to the rapid and direct determination of iodide in seawater with long-term durability.

A Computer-Based Undergraduate Exercise Using Internet-Accessible Simulation Software for the Study of Retention Behavior and Optimization of Separation Conditions in Ion Chromatography

An ion chromatography exercise is described that uses a free Internet-based software package, Virtual Column 2, to simulate retention behavior and to optimize separation conditions. Virtual Column 2 permits the detailed study of retention behavior of inorganic anions on a Dionex AS11 column using isocratic hydroxide eluents and also on a Dionex AS4A–SC column using carbonate-bicarbonate eluents. Collection of retention data from Virtual Column 2 allows students to investigate the effects of variation in eluent composition on retention, to examine separation selectivity in ion chromatography, and to evaluate the performance of simple retention models. Because the retention data provided by the software are based on actual experimental measurements an accurate evaluation of these models is possible. Effects of peak shape on resolution are also studied and the software can be used to perform computer-assisted optimization of separation conditions. The entire exercise, including familiarization with the software, takes about four hours and can be adjusted to fit into a shorter time frame if necessary. The ability to scan retention data over a wide range of eluent composition opens up the possibility of a computerized selection of the optimal separation conditions. The major characteristics of retention behavior, peak-shape effects and pH effects evident in ion chromatography (IC) using common stationary phases and eluents are illustrated.

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.

Effect of eluent composition on retention behavior of anions in ion chromatography on anion-exchangers modified with heparin

Effects of eluent composition on retention behavior of inorganic anions have been investigated in ion chromatography using anion-exchangers modified with heparin. Both cation and anion of the eluent affected the retention of analyte anions and unusual retention behavior was observed on the modified stationary phase. The retention time of anions decreased with decreasing eluent concentration when sodium sulfate, magnesium sulfate and chlorides of alkali metals were used as the eluent, whereas it increased with decreasing eluent concentration when aluminum sulfate, copper sulfate and sulfuric acid were used as the eluent. The retention of nitrate increased in the order of Li +, Na +, K +, Rb + and Cs + when their chlorides were used as the eluent. When sodium perchlorate and chlorides of alkaline-earth metals were used as the eluent, the eluent should include heparin. Otherwise, the modifier was partially bled from the column.

Ion chromatography using anion exchangers modified with heparin

Retention behavior of inorganic anions and cations on anion exchangers modified with heparin has been investigated. Retention of anions on the anion exchanger was remarkably reduced after the modification with heparin. The cations of the elu- ent affected the retention behavior of ions. The retention factor of anions decreased with decreasing eluent concentration when sodium sulfate and magnesium sulfate were used as the eluent, whereas it increased with decreasing eluent concentration when aluminium sulfate, copper sulfate and sulfuric acid were used as the eluent. When copper sulfate was used as the eluent, both anions and cations were retained on the modified stationary phase and simultaneous separation of both anions and cations were carried out. Cations as well as non-UV-absorbing anions were indirectly visualized by copper ions.

Evaluation of sulfobetaine-type zwitterionic stationary phases for ion Chromatographic separation using water as a mobile phase

Ion Chromatographic separation of inorganic ions (anions and cations) was investigated by using three kinds of sulfobetaine-type surfactants (CHAPS, C12SB, and C14SB) as the stationary phases, which were coated by hydrophobic adsorption on the ODS column. In the present separation system, pure water was used as a mobile phase. Since the amount of surfactant adsorbed on the ODS surface significantly influenced the retention behaviors of inorganic ions, the amounts of the sulfobetaine-type surfactants adsorbed were estimated by the breakthrough procedure. The maximum amounts of CHAPS, C12SB and C14SB adsorbed were 0.40, 0.87 and 1.08 mmol, respectively. It was elucidated from the chromatograms of inorganic ions that the retention behavior of inorganic anions was directly related to the surface charges arising from the adsorbed surfactants. The large surface charge was effective for the efficient separation of inorganic ions in water elution. In addition, their retention behavior was strongly affected by the hydrophobicity of the adsorbed surfactants as well as the ionic functional groups of the surfactants which produced the charged surface. The elution order of inorganic anions was correlated with the Hofmeister series. This suggests that the hydration energies of the ions play important roles in separation in the water elution system.

Retention behavior of inorganic anions and organic acids on polymer-coated C18 column coated with cetyltrimethylammonium ion by ion chromatography with indirect UV-photometric detection.

環状シロキサンで被覆された高性能なシリカ系C18カラム(CapcellTM pakC18)とセチルトリメチルアンモニウムイオンから調製される陰イオン交換カラムの有用性を実証するために,この陰イオン交換カラムにおける無機陰イオン及び有機酸の保持特性について,トリメリト酸溶離液を用いる間接紫外吸光検出イオンクロマトグラフィーにより検討を行った.その結果,調製した陰イオン交換カラムは,C18基及びセチル基に起因する疎水性を有することから疎水性の無機陰イオン及び有機酸を強く保持する傾向が見られた.又,カラムから溶出した親水性及び疎水性の無機陰イオン及び有機酸のピーク形状が非常に良好であったことから,この陰イオン交換カラムは高性能なイオンクロマトグラフィー用のカラムであることが実証された.本カラムを雨水及び雨水による土壌溶出水中の陰イオンの定量に適用したところ良好な結果が得られた.