Ion selective electrodes in ion chromatography

Abstract

The number of applications of potentiometric detection In Ion chromatography Is Increasing In the use of ion selective electrodes for which the response Is not limited to a few number of Ions. In this research, membrane electrodes, for a number of Ions, based on PVC were prepared to examine selectivity, detection limit and reproducibility for chromatographic and flow-injection measurements via mixed solution method and flow-injection technique. The selectivity sequence of anion selective electrodes for single charged Inorganic anions was F< Cl < Br < NO 2< NO 3<I. This was Ll +< Nil+< Cs+< Na+< K+ for cation selective electrodes. The 4 detection limits for most of anions and cations were found to be at the nanogram or picogram levels. Response times of bromide and chloride electrodes were established to concentration and flow-rate changes in a flowing stream. When flow-rate was Increased, response time of electrode decreased, but response volume Increased. Response time was decreased for low activities rather than high activities of solute ion when flow-rate Increased. At high flow-rates, response time was Independent of the activity of the solute Ion. Also a new approach to the definition of the response time in flowing conditions was purposed In order to be able to Indicate their performances. An evaluation of the Influence and contribution of the sample dispersion on the sensitivity of tubular liquid membrane bromide selective electrode based on PVC was examined with a new, easy reliable approach In a flow-injection system for chromatographic measurements. Using water as carrier, it was observed that the dispersion Influence was completely dependent on the response time of electrodes. When sample In the carrier passes through the electrode surface just within the electrode response time, better peak shape and sensitivity were obtained at each flow-rate, whilst shorter remaining time of sample caused tailing and decreasing of the sensitivity, longer remaining time caused peak broadening. An all solid-state tubular PVC-matrix membrane electrode as detector In non-suppressed Ion chromatography was employed Jor detection of some monovalent common anions Including I and SO at sub-ppb levels. Non-supprýessed separation of halides and strongly retained anions I and SCN In one run was achieved using Phosphate solution as a new efficient eluent over Dionex IonPac-AS4A and AG4A columns. Potentlometric detection of eleven monovalent Inorganic and organic anions with the use of all solid-state contact tubular membrane electrode (cell volume 2 pl) as detector In non-suppressed Ion chromatography was demonstrated using phosphate and hydrogen phosphate as eluents at low concentrations. Theoretical and practical considerations were discussed, and In particular, sensitivity, linearity, detection limit and dynamic behaviour were presented. Applications to river, drinking and rain water samples were described. In any liquid chromatographic technique, the eluent composition provides greatest flexibility for manipulating the retention of solutes In order to achieve a desired separation. Utilizations of a new composition of the 11CO 3 /CO 32 buffer solution or phosphate solution as eluents were demonstrated for the separation of twelve Inorganic and organic anions with good resolution in six minutes using Dionex-100 ion chromatographic system. A simple and selective method for single Ion chromatographic 11 separation (in seven mlnVtesý and potentiom+etric detection (at sub-ppb levels) of Na"', Nil 4, K. Rb +0 THA +0 Cs and Tl+ cations was established using copper and magnesium salts as eluents, with Dionex IonPac-CS3 analytical and guard columns and all solid-state contact tubular membrane potassium selective electrode as detector. The application of the method for drinking, river, spring, sea water samples and orange juice, urine and saliva samples were illustrated. As the detector was highly selective and sensitive to only monovalent cations, no Interference from other cations, the method was easily applIjd to mjny sample types examples Including the determination of Na and K, on the surface of the glassware adsorbed during the fabrication stage, and In many inorganic and organic chemicals were given. It might be the over-all efficiency of Ion chromatographic procedures that allows the routine separation and detection of Inorganic and organic anions and cations at low levels in a simultaneous system. A simple, selective, sensitive reproducible and rapid method needing only 8 minutes or less to complete a simultaneous potentiometric detection and Independent separation of a group of fourteen Inorganic and organic monovalent common anions and cations was developed using copper or magnesium sulphate salt as eluents with Dionex 1onPac-AS4A and -CS3 anion and cation-exchange columns In tandem. The only difference of the method from other simple chromatographic applications was just one more chromatographic column and one more potentiometric detector. The method was flexible, as the anions will not Interfere with the detection of cations or cations will not Interfere with the detection of anions, that detectors can be used at the end of the two column In tandem or one can be used af ter f Irst column. The first column can be anion or cation-exchange. A method for simultaneous determination of sodium, potassium and chloride In bovine serum albumin plasma was established. it Involved Independent Ion chromatographic separation on anion and cation- exchange columns and simultaneous potentiometric detection by anion and cation selective electrodes. The concentrations of monovalent cations and chloride was Increased with the Increasing of dilution of non-filtered sample, there was no significant changes In the concentrations determined In the sample which was filtered.