John R. Stillian

New membrane-based electrolytic suppressor device for suppressed conductivity detection in ion chromatography

Abstract This paper discusses the newest advancement in chemical suppression preceding conductivity detection. The new suppressor uses electrolysis of deionized water to generate the required acid or base for the suppression neutralization reaction and utilizes the electrical field to enhance, through electrodialysis, the suppressors capacity for neutralization. The suppressor is able to accommodate eluents as high as 150 mM NaOH, without the need for a separate regenerant solution, by recycling the conductivity detector cell waste to the regenerant and electrolysing the water in the waste stream to the required acid or base. The device is able to use deionized water as regenerant and neutralize the eluent stream to deionized water without the expected increase in resistance by employing ion exchange material in intimate contact with the electrodes and the membranes. The current is carried with low resistance through the ion-exchange material via ion transport from one ion-exchange site to another.

Factors controlling ion-exchange selectivity in suppressed ion chromatography

The control of ion-exchange selectivity is the most important means of moderating separations in suppressed ion chromatography. Selectivity variations are primarily achieved through the use of different stationary phases, hence the construction of the stationary phase plays a key role. The major factors which determine the selectivity of the ion-exchange phase are: the polymer composition of the stationary phase, the type of ion-exchange site and the structure of the ion-exchange site. The eluent can also play a significant role in determining the overall selectivity of an ion-exchange separation. The mobile phase parameters which affect the separation selectivity are: the choice of eluent ion, the concentration (and pH) of the eluent, the presence of non-ionic eluent modifiers and the eluent temperature.

New latex-bonded pellicular anion exchangers with multi-phase selectivity for high-performance chromatographic separations

Abstract A new polymeric “multi-phase” chromatographic packing material that combines ion exchange in a pellicular format with adsorption and ion-pair retention on a neutral macroporous core bead is described. The material is stable from pH 0 to 14 and from 1 to 100% (v/v) of common reversed-phase solvents in aqueous mixtures. The ability of independently control ion exchange and adsorption or ion-pair retention is demonstrated on a variety of inorganic and organic analytes.

Capillary electrophoresis of inorganic anions and organic acids using suppressed conductivity detection strategies for selectivity control

The use of suppressed conductivity as a detection scheme for capillary electrophoresis (CE) is described. A comparison is made between several electrolytes for CE with suppressed conductivity detection (CESC) in terms of efficiency of separation and peak shape. The ability to modify electrophoretic mobility and selectivity as a function of temperature and electrolyte ionic strength is demonstrated. The separation of a variety of low-molecular-mass organic acids is optimized using the addition of metal ions to the separation electrolyte.

Practical aspects on the use of organic solvents in ion chromatography

Organic solvents play an important role in ion chromatography. The advent of solvent-compatible ion-exchange stationary phases permit all proportions of organic eluents to be employed. Selectivity mediation for the ion-exchange process is the most important usage of solvents. Changing the retention characteristics of the column packing toward the analyte permits the analyst to alter retention order, peak efficiency and resolution to optimize the separation. Column clean-up of organic molecules is also dramatically enhanced by addition of solvent. Several examples are offered to describe the utility of organic solvents in modern ion chromatography.

Determination of anions and cations in concentrated bases and acids by ion chromatography : electrolytic sample pretreatment

Abstract The development of a high-capacity electrochemical membrane suppressor has resulted in new ion chromatographic methods for the determination of trace ions in concentrated acids and bases. Unlike previous membrane suppressors, the new one does not require chemical regeneration, thus eliminating regenerant leakage across the membranes. The new suppressor electrolyses water to create the acid or base required for neutralization and thus permits contamination-free acid-base neutralizations of concentrated reagents. This makes the new suppressor ideal for sample pretreatment of acids or bases prior to analysis by ion chromatography. This technique has been applied to trace anion determination in concentrated bases ( e.g. 50% NaOH and concentrated NH 4 OH) and trace cation determination in concentrated acids ( e.g. 48% H 2 SO 4 , 43% H 3 PO 4 and 33% methane sulfonic acid). The detection limits for most ions are 1 to 10 ng/ml.

Preconcentration determination of inorganic anions and organic acids in power plant waters separation optimization through control of column capacity and selectivity

Abstract An anion-exchange column has been developed for the separation of anions inpower plant waters. The column has been optimized, in terms of capacity and selectivity, to allow the isocratic separation of weakly retained organic and inorganic anions, in addition to more strongly retained anions. This new moderate capacity anion-exchange column was utilised for the preconcentration ion chromatography (IC) determination of key anions, at low μg/l levels, in a numver of power plant waters. Correlation coefficients obtained for linearity plots of fluoride, acetate, formate, chloride, nitrite, sulfate and oxalate in pure water, ammoniated and morpholinated waters were in the range 0.996–0.999. The correlation coefficients obtained for the seven anions in borated water were in the range 0.995–0.999, except for fluoride and chloride, which were 0.993 and 0.991, respectively.

Separation and detection of group I and II cations by ion chromatography

Abstract Lithium, sodium, magnesium and calcium are routinely monitored in environmental samples and in analysis of ultrapure water for semiconductor and power generation facilities. The use of graphite furnace, atomic absorption and ICP have long been recognized as the analytical instruments of science for the detection and quantization of these cations. These spectral detectors detection method of choice of because of their inherent speed, sensitivity, and lack of interferences. This paper will present results of a recent advance using ion chromatography with chemical suppression and conductivity detection for group I and group II cations. The method allows the separation and detection of lithium, sodium, ammonium, potassium, magnesium, calcium and morpholine at the sub-μg/l levels in ultrapure water and common power plant waters.

Factors affecting the ion chromatographic preconcentration behaviour of inorganic anions and organic acids

Abstract An ion chromatograph employing an IonPac AC10 concentrator column and AS10 analytical column with an hydroxide eluent was used to investigate the preconcentration behaviour of inorganic anions and organic acids. Increased sample loading volumes resulted in decreased recoveries for weakly retained solutes, while the flow-rate at which the sample was loaded did not affect solute recovery, at least for flow-rates up to 5.0 ml/min. The recoveries obtained for weakly retained solutes were also influenced by the presence of sample matrix ions and the ion-exchange selectivity of the concentrator column. Formate and chloride were found to modestly decrease the recovery of fluoride, while the presence of sulfate had a more significant impact. Sample matrix effects were minimized by using a concentrator column with an ion-exchange selectivity that permits maximum retention of solutes, such as fluoride and formate, yet only moderate retention of anions, such as sulfate and oxalate.

Improved method for the determination of manganese in nuclear power plant waters

Abstract An improved method for manganese determination in nuclear power plant waters has been developed. This method combines a selective chelation concentration method with a unique analytical separation for manganese from the interfering matrix using a weak acid cation exchange column. The detection sensitivity by conventional post-column derivatization is improved with the combination of chemical eluent suppression and subsequent post-column derivatization. The detection limit for manganese in ammonium matrix is approximately 2 pg/ml and the limit of quantitation 10 pg/ml with 100 ml sample volume.