Application of ion chromatography for the investigation of the anionic and cationic composition in high-purity water production

A suitable and sensitive ion chromatographic measuring system for determining the main components at nanogram to milligram per liter levels in water samples from the electrodeionization process is presented. A modified Dionex system offers the possibility for the determination of anions and cations in the samples at ng/L, μg/L and mg/L levels. The ng/L level of anions and cations in 20–130 mL high-purity water can be analyzed immediately after preconcentration on appropriate exchange columns. The mg/L level samples are successfully determined by use of an auto-sampler. The quantification of each ion is achieved using the suppressor technique and a conductivity detector. Samples are taken from 5 steps of the electrodeionization process and stored in pre-cleaned FEP (fluorinated ethylene propylene) at 7 °C in darkness prior to the determination of chloride, nitrate, sulfate, carbonate, sodium, ammonium, potassium, calcium and magnesium. Eluents, ultrapure water and samples for the determination of carbonate were passed through special glass containers and flushed with helium gas to avoid the effect of atmospheric carbon dioxide. Results of the investigation of the cationic and anionic composition in water samples within the electrodeionization process are presented and discussed. Received: 12 October 1998 / Revised: 16 December 1998 / Accepted: 19 December 1998     

Determination of anions in high-purity water by ion chromatography

Summary The determination of the concentration of some different anions in high-purity water (g/l-level) using ion chromatography after concentration on pre-columns is described. The detection ist made by a conductivity cell after passing an anion fiber-suppressor (AFS). Two different separator columns (AS-5 and AS-4) and some different separator systems were tested. In all cases linearity is given for the determined anions.The concentration of the anions was determined not directly but by addition of a standard solution and subsequent graphic extrapolation of the calibration diagram. The determination levels are below 1 g/l. The AS-5 column gives better results than the AS-4 column.

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Ionen-chromatographische Bestimmung von Anionen in Reinstwasser

Zusammenfassung Die Bestimmung der Konzentration verschiedener Anionen in Reinstwasser (g/l-Bereich) mittels der Ionen-Chromatographie nach Anreicherung auf Konzentriersäulen wird beschrieben. Die Detektion erfolgt über eine Leitfähigkeitsmeßzelle mit vorgeschaltetem Anionen-Hohlfasermembransuppressor (AFS). Es wurden zwei verschiedene Trennsäulen (AS-4 und AS-5) und mehrere Trennsysteme getestet und optimiert. In allen Fällen ergab sich Linearität für die untersuchten Anionen. Die Bestimmung der Anionenkonzentrationen in Reinstwasser erfolgte nicht direkt, sondern durch Aufstocken mit Standardlösung und anschlie\ender graphischer Extrapolation der erstellten Eichgraden. Die Nachweisgrenzen liegen unter 1 g/l. Die AS-5-Säule erwies sich für die beschriebene Methode als geeigneter.

     

Role of ion pairing in anionic additive effects on the separation of cationic drugs in reversed-phase liquid chromatography

Mobile phase additives can significantly affect the separation of cationic drugs in reversed-phase liquid chromatography (RPLC). Although there are many applications for anionic additives in RPLC separations, the retention mechanism of basic drugs in the presence of inorganic and highly hydrophilic anionic species in the mobile phase is not at all well understood. Two major retention mechanisms by which anionic additives can influence the retention of cations are: (1) ion pair formation in the mobile phase with subsequent retention of the neutral ion pair; (2) pre-sorption of anionic additives on the stationary phase followed by "dynamic ion-exchange" or "electrostatic interaction" with the analytes. Because the use of ion pair chromatography in the separation of proteins, peptides, and basic drugs is rapidly increasing, understanding the retention mechanism involved is becoming more important, especially for the smaller commonly used hydrophilic anionic additives (e.g., formate HCOO, chloride Cl-, trifluoroacetate CF3COO-, perchlorate ClO4-, and hexafluorophosphate PF6-). In this work, we compared various anionic additives in light of their effects on the retention of basic drugs. As did many others we found that the addition of anionic additives (Cl-, CF3COO-, ClO4-, PF6-) profoundly influences the retention of basic drugs. In order to explain the data and differentiate the mechanisms by which the anionic additives perturb the chromatography, we used ion pair formation constants independently measured by capillary electrophoresis (CE) under the mobile phase conditions (pH, solvent composition) identical to those used in chromatography. Agreement between the predicted and experimental chromatographic data under various conditions was evaluated. Under specific circumstances (e.g., pH, stationary phase, and nature of anionic additive), we conclude that the ion pair mechanism is more important than the dynamic ion-exchange and at other conditions it remains a significant contribution.     

Separation and quantitation of monovalent anionic and cationic species in mainstream cigarette smoke aerosols by high-performance ion chromatography

A simple method has been developed to separate and quantitate monovalent ionic species in mainstream cigarette smoke aerosols based on ion chromatography (IC) with conductivity detection. The method entails collecting the smoke aerosol particulate phase by electrostatic precipitation, dissolving the smoke condensate in methanol (MeOH), and separating the ionic species on either a cation- or anion-exchange column. The method has been applied to the analysis of smoke aerosols from two cigarettes, 1R4F Kentucky Reference cigarettes and a new cigarette that heats but does not burn tobacco. The predominant cations in smoke aerosols from 1R4F Kentucky Reference and the new cigarettes are sodium (Na+), ammonium (NH4+), and potassium (K+) ions; the predominant anions are acetate (AcO-) and formate (HCOO-). Trace amounts of chloride (Cl-), nitrite (NO2-), and nitrate (NO3-) ions are also present.     

Analysis of wastewater for anionic and cationic nutrients by ion chromatography in a single run with sequential flow injection analysis

To prevent nutrient enrichment and, hence the undesirable ecological impacts, the nutrients monitored in wastewater samples include two anionic species, i.e., nitrate and orthophosphate, and a cationic species, ammonium. Ion chromatography (IC) is one of the popularly used techniques for determinations of nitrate and phosphate in these samples, whereas determination of ammonium in wastewater samples is typically done using manual or automated wet chemistry, e.g., flow injection analysis (FIA). We have developed a sequential IC–FIA method, using Lachat’s QC8000 IC system, which allows determinations of nitrate, phosphate and ammonia in a single injection. In this system, a QuikChem Small Suppressor cartridge is regenerated in between the samples. A sample is injected while leaving the suppressor off-line. Ammonium, a cation, elutes in the void volume of an anion-exchange column. The unsuppressed column effluent, exiting the conductivity flow cell, up to this point is used for FIA determination of ammonia. When ammonia exits the conductivity flow cell, a fully regenerated suppressor is brought in-line for conductometric detection of the anions. Analog data are simultaneously acquired from colorimetric and conductometric detectors, for the cationic and anionic nutrients, respectively. The method is accurate with spike recoveries in wastewater samples ranging from 91% for nitrate to 114% for chloride. It is precise with RSD values, for replicate analyses (n=7) of a mid-range standard, ranging from 0.4% for phosphate to 1% for nitrate.     

Retention model for the separation of anionic metal-EDTA complexes in ion chromatography

A retention model is derived for complex anions eluted from an anion-exchange column with multiple ionic eluents containing hydrogencarbonate, carbonate, and hydroxyl species and the sample solution, containing transition metals, anions and complexing ligand. The theory is based on the generalized ion-exchange equilibrium, protonation and complex-formation equilibria. The unknown parameters of chromatographic ion-exchange equilibrium constants for sample and eluent species are determined from the experimental retention data by iterative minimization, using a non-linear regression algorithm. The model was utilized to predict the retention behaviour of CdEDTA²⁻, CoEDTA²⁻, MnEDTA²⁻ and NiEDTA²⁻ ions. The capacity factors of complex ions were determined for wide ranges of pH values and eluent concentrations. Good agreement was obtained between the observed and predicted retentions.     

Polymer-supported cationic templates for molecular recognition of anionic hosts in water

Translocating solution-phase molecular recognition of oppositely charged hosts and guests to the solid phase represents a major challenge; we report a successful immobilisation strategy which allows selective host-guest interactions in water unencumbered by unwanted ion exchange-type interactions.     

Ultra-pure water for ion chromatography

Water with ionic concentrations substantially below 1 μg/l is an increasing requirement for high sensitivity ion chromatographic analysis. The resistivity of the water is not an adequate guide to impurity levels at less than 1 μg/1 due to the practical limitations in resistivity measurement and to the non-linear variation of resistivity with impurity ion concentration. A water purification system is described using inter-stage monitoring to overcome these limitations and to ensure ultra-trace ionic levels. Some examples of cation analyses are included.     

Barriers to ion translocation in cationic and anionic receptors from the Cys-loop family

Understanding the mechanisms of gating and ion permeation in biological channels and receptors has been a long-standing challenge in biophysics. Recent advances in structural biology have revealed the architecture of a number of transmembrane channels and allowed detailed, molecular-level insight into these systems. Herein, we have examined the barriers to ion conductance and origins of ion selectivity in models of the cationic human alpha7 nicotinic acetylcholine receptor (nAChR) and the anionic alpha1 glycine receptor (GlyR), based on the structure of Torpedo nAChR. Molecular dynamics simulations were used to determine water density profiles along the channel length, and they established that both receptor pores were fully hydrated. The very low water density in the middle of the nAChR pore indicated the existence of a hydrophobic constriction. By contrast, the pore of GlyR was lined with hydrophilic residues and remained well-hydrated throughout. Adaptive biasing force simulations allowed us to reconstruct potentials of mean force (PMFs) for chloride and sodium ions in the two receptors. For the nicotinic receptor we observed barriers to ion translocation associated with rings of hydrophobic residues-Val13' and Leu9'-in the middle of the transmembrane domain. This finding further substantiates the hydrophobic gating hypothesis for nAChR. The PMF revealed no significant hydrophobic barrier for chloride translocation in GlyR. For both receptors nonpermeant ions displayed considerable barriers. Thus, the overall electrostatics and the presence of rings of charged residues at the entrance and exit of the channels were sufficient to explain the experimentally observed anion and cation selectivity.     

Determination of trace metallic impurities in high-purity quartz by ion chromatography

A method has been developed for the determination of relevant trace impurities (alkali, alkaline and transition metals) in high purity quartz by ion-chromatography. In situ reagent (HF) purification and simultaneous sample dissolution was achieved in a multichannel vapour phase digestion assembly. Twenty-one samples can be digested at a time in this vapour phase system. Significant decrease in the process blank levels for all the analytes was observed. Drastic reduction (250 times) of NH4+ blank was achieved in the described vapour phase digestion, which enables the determination of trace concentration of sodium in high purity quartz. After volatilisation of the matrix and unreacted HF, the clear water leached solutions were injected into an ion-chromatograph equipped with conductivity detector for the determination of alkali and alkaline earth metals. In the case of transition metals, the trace residues were leached with 10 mM HCl and after separation on a mixed bed analytical column (IonPac CS5) were detected by spectrophotometry after post column derivatisation using 4-(2-pyridylazo)resorcinol (PAR). The accuracy of the result was checked by their comparison with those obtained by independent methods like inductively coupled plasma (ICP) MS and ICP atomic emission spectrometry. The achievable detection limits are between 0.4 ng/g (Li) and 22 ng/g (Mn). The application of the method to the determination of the above trace metals in two high-purity-grade quartz samples is demonstrated.     

Dual-opposite injection electrokinetic chromatography for the unbiased, simultaneous separation of cationic and anionic compounds

The concept of dual opposite injection in capillary electrophoresis (DOI-CE) for the simultaneous separation, under conditions of suppressed electroosmotic flow, of anionic and cationic compounds with no bias in resolution and analysis time, is extended to a higher pH range in a zone electrophoresis mode (DOI-CZE). A new DOI-CE separation mode based on electrokinetic chromatography is also introduced (DOI-EKC). Whereas conventional CZE and DOI-CZE are limited to the separation of charged compounds with different electrophoretic mobilities, DOI-EKC is shown to be capable of separating compounds with the same or similar electrophoretic mobilities. In contrast to conventional EKC with charged pseudostationary phases that often interact too strongly with analytes of opposite charge, the neutral pseudostationary phases appropriate for DOI-EKC are simultaneously compatible with anionic and cationic compounds. This work describes two buffer additives that dynamically suppress electroosmotic flow (EOF) at a higher pH (6.5) than in a previous study (4.4), thus allowing DOI-CZE of several pharmaceutical bases and weakly acidic positional isomers. Several DOI-EKC systems based on nonionic (10 lauryl ether, Brij 35) or zwitterionic (SB-12, CAS U) micelles, or nonionic vesicles (Brij 30) are examined using a six-component test mixture that is difficult to separate by CZE or DOI-CZE. The effect of electromigration dispersion on peak shape and efficiency, and the effect of surfactant concentration on retention, selectivity, and efficiency are described.     

Application of extraction chromatography for analysis of high-purity CdTe and ZnSe

Summary The possibilities of extraction chromatography are investigated for the separation of impurities from high-purity CdTe and ZnSe. The conditions of a quantitative separation of the impurities are determined. As a result of the investigations the techniques are developed for neutron activation analysis of CdTe and spectral analysis of ZnSe, the impurity-detection limits being from 10^–5% to 10^–7%.

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Die Anwendung der Extraktionschromatographie zur Analyse von hochreinem CdTe und ZnSe

Zusammenfassung Die Möglichkeiten der Extraktions-Chromatographie für die Anreicherung von Mikrobeimengungen in hochreinem CdTe und ZnSe wurden untersucht. Dazu wurden die Bedingungen der quantitativen Trennung von Mikrobeimengungen in Cd, Te und Zn ermittelt.Als Ergebnis der Untersuchungen wurden Methoden der Neutronen-Aktivierungsanalyse von ZnSe ausgearbeitet. Bei der Kombination der extraktions-chromatographischen Anreicherung mit diesem Analyseverfahren beträgt die Bestimmungsgrenze für Mikrobeimengungen 10^–5–10^–7%.

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Presented at the 9th International Symposium on Microchemical Techniques, Amsterdam, August 28—September 2, 1983.     

High-capacity lithium-rich cathode oxides with multivalent cationic and anionic redox reactions for lithium ion batteries

Lithium-rich cathode oxides with capability to realize multivalent cationic and anionic redox reactions have attracted much attention as promising candidate electrode materials for high energy density lithium ion batteries because of their ultrahigh specific capacity. However, redox reaction mechanisms, especially for the anionic redox reaction of these materials, are still not very clear. Meanwhile, several pivotal challenges associated with the redox reactions mechanisms, such as structural instability and limited cycle life, hinder the practical applications of these high-capacity lithium-rich cathode oxides. Herein, we review the lithium-rich oxides with various crystal structures. The multivalent cationic/anionic redox reaction mechanisms of several representative high capacity lithium-rich cathode oxides are discussed, attempting to understand the origins of the high lithium storage capacities of these materials. In addition, we provide perspectives for the further development of these lithium-rich cathode oxides based on multivalent cationic and anionic redox reactions, focusing on addressing the fundamental problems and promoting their practical applications.     

Analysis of cationic nutrients from foods by ion chromatography

This paper describes the feasibility of combining two relatively new technologies to generate data on the cationic nutrient content of foods. Single column ion chromatography was used to monitor several analytes following the use of a microwave digestion scheme aimed at rapid, multiple sample digestion. The result is a more streamline and productive approach to multi-sample preparation and multi-analyte determination when investigating the cation content of foods.

Linearity and limits of detection for the chromatographic procedure were established. Sample size as well as digestion acid type and amount were investigated during the microwave process. The method was applied to a variety of food matrices to evaluate its scope. Results generated with this method compare favorably to those from atomic absorption.

Finally, capillary ion electrophoresis (Waters' trade name: Capillary Ion Analysis), a subset of capillary electrophoresis which has been optimized for ion analysis, was applied to the sample digest to investigate the usefulness of this technology to the analysis of mono-/divalent cations from foods.     

Purge-and-trap ion chromatography for the determination of trace ammonium ion in high-salinity water samples

It has always been assumed that purge-and-trap (P&T) method is only used for the analysis of volatile organic compounds (VOCs) in aqueous samples. In this paper, a novel P&T preconcentrator has been developed for the determination of trace amounts of ammonium ion in high-salinity water samples by ion chromatography (IC). Method performance is evaluated as a function of concentration of assistant purging material, purging time, and flow rate. Under the optimum P&T conditions with the purified nitrogen gas at flow rate 40 mL/min for 15.0 min at 40 degrees C, the overall collection efficiency is independent of the concentration of ammonium over the range 1.2-5.9 microM. The enrichment factor (EF) of ammonium correlates the ratio of the sample volume to the acceptor solution volume in the trap vessel, providing potentially unlimited increase of the ammonium signal. Our results indicate that environmental samples with low levels of ammonium in matrices with high concentrations of sodium can be easily analyzed and the detection limit down to 75 nM (1.35 ppb) level, corresponding to picomole of ammonia in the injected sample. Calibration graph was constructed with ammonium standards ranging from 0.05 to 6.0 microM and the linearity of the present method was good as suggested by the square of correlation coefficients being better than 0.997. Thus, we have demonstrated that the P&T-IC method allows the routine determination of ammonium ion in seawater samples without cation interferences.     

Comparative activity of aqueous dispersions of CdS nanocrystals stabilized by cationic and anionic polyelectrolytes in photocatalytic hydrogen production from water

The results of a study on the photocatalytic activity of aqueous dispersions of Ni-doped CdS nanocrystals (NCs) covered with an amphiphilic polyelectrolyte (PE) shell, i.e., a polycation (NC-PC) or polyanion (NC-PA), are presented for the first time. The H₂ evolution rate measured under identical conditions served as a measure of activity. The NC-PC and NC-PA samples were characterized by similar PE content (~40%) and monomodal size distribution. According to our calculations based on the NC dimensions and lattice parameters, about one macromolecule of the PE is required to stabilize one NC. The average hydrodynamic diameter of the NC-PC was found to be 1.5 times larger than that of the NC-PA due to the difference between their chemical structures and different abilities of ionogenic groups to dissociate. The photocatal ytic activity of the PE-stabilized CdS nanocrystals was significantly influenced by the type of the PE, while the H₂ evolution rate depended on the reducing medium used during the process. When the medium contained Na₂S or when the PE-stabilized NCs were pretreated with Na₂S, the effect of the shell type was more pronounced and the activity of NC-PA was 2 to 14 times higher than that of NC-PC.     

Interaction of chromophores in dissimilar associates of cationic and anionic polymethine dyes in water

A strong interaction between chromophores of cationic and anionic components was found based on the analysis of electronic absorption spectra of aqueous solutions of mixtures of cationic indopolycarbocyanines with anionic cyanines. Strong dissimilar 1∶1 associates are formed. Association constants were estimated spectrophotometrically. The main factors determining the degree of interaction of chromophores were revealed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 950–955, May, 1997.