What are the unanswered (and unasked) questions in ion analysis?

A risk-based approach to validation of ion chromatography methods using suppressed conductivity

Ion chromatography (IC) has evolved into one of the most widely used separation techniques of analytical chemistry. Consequently, the number of users of this method is continuously growing. Analysts often assume that widely used guidelines for HPLC method validation in regulated environments routinely apply to IC. This manuscript provides an analysis of the potential shortcomings of traditional approaches to development and validation of IC methods using suppressed conductivity detection and a risk-based alternative approach to these activities. The goal of the alternative approach is a reduction in the risk of erroneous determinations of analytes when IC methods using suppressed conductivity detection are employed.

Assuring precision and calibration linearity in ultrasensitive suppressed ion chromatography by using deliberately contaminated hydroxide eluent

EXPERIMENTAL

and theoretical studies were conducted to investigate low and non-linear responses in sub-micro molar-level suppressed ion chromatography with a hydroxide eluent. A calculated response was derived using experimentally determined detector effluent ion composition data and compared with measured experimental responses. The calibration curve was non-linear, and its slope varied considerably with different instrumental setups and operating conditions. The non-linearity of the solution conductivity response was determined by two acid-base equilibria of water and carbonic acid, and fluoride ion. By using eluent contaminated with para-toluene sulfonate at micro molar level, the non-linear response was greatly alleviated.

A comparative study on dissolution rate of sintered (Th-U)O2 pellets in by microwave and conventional heating

ThO2 with approximately 3% 233UO2 is the proposed fuel for the Advanced Heavy Water Reactor (AHWR) and characterized as a mixed oxide (MOX) fuel. Due to the existence of a single oxidation state, quantitative dissolution of MOX samples like (Th-U)O2 and (Th-Pu)O2 is a challenging task for any analytical chemist. However, dissolution is a pre-requisite for complete characterization of the fuel. The present paper describes a detailed study carried out on the comparison of dissolution of sintered (Th-U)O2 mixed oxide pellets, in 16 M HNO3 using microwave and conventional heating techniques, under reflux conditions. The study was carried out with variation of parameters such as concentration of HF and UO2 substitution in the MOX solid solution. The concentration of dissolved U and Th was determined by modified Davies and Gray potentiometric titration and Th-EDTA complexometric titration using xylenol orange as the titration end point indicator respectively. Experimental results clearly indicate that the microwave heating assisted dissolution rate is 2 to 3 times higher than the conventional infrared heating assisted dissolution rate, for sintered pellets. The concentration of HF is a critical parameter, an excess leads to precipitation of insoluble ThF4. The concentration of HF was optimized to 0.025 M. Experimental results also clearly show that at this concentration of HF in 16 M HNO3, a higher substitution of UO2 in MOX solid solution also facilitates the dissolution process. Different trace metal impurities were determined in the MOX samples after dissolving by microwave and infra red heating techniques and it was observed that the results are comparable.

Determination of alkali and alkaline earth elements along with nitrogen in uranium based nuclear fuel materials by ion chromatography (IC)

An accurate and sensitive ion chromatographic (IC) method with suppressed conductivity detection is described for determination of traces of Na, K, Mg and Ca along with nitrogen in uranium based materials. The method involves matrix separation after sample dissolution by hydrolyzing and filtering off the polyvalent cations. Transition elements interfering in the determination of Ca were removed by cation exchange cartridge containing iminodiacetate resin. Detection limits were between 2 and 6 microgL(-1) and overall precision were better than +/-5%. Recovery of spiked cations was in range from 96% to 104%. Results obtained were in good agreement with other methods.

Quality control techniques for routine analysis with liquid chromatography in laboratories

The process of quality assurance should demonstrate that the method and the analytical instrument provide accurate and precise results, or whether deterioration occurs. For this, the quality procedure should include tests which provide information on the characteristic performance of the method. According to the recent literature, useful procedures contributing to the overall quality of analytical results are illustrated in relation with liquid chromatography. Parameters examined are carry-over, column statement, accuracy and precision. The performance of the whole system from the extraction to measurement of analytes of interest must be monitored with control charts. Data representing the routine performance of chromatographic equipment systems and method allow predicting long-term uncertainties and confidence intervals.

A new method of ion chromatography technology for speedy determination and analysis in organic electrosynthesis of glyoxylic acid

Based on ion chromatography (IC) technology, we have developed a new method that combines ion chromatography with a conductivity detector to separate and determine the substances of glyoxal, glycolic acid, oxalic acid and glyoxylic acid. The ion chromatography was applied for the first time in quantitative determination of substances involved in electrosynthesis of glyoxylic acid. The method has been applied to separate and analyze simultaneously either glyoxylic acid and glyoxal in electroxidation of glyoxal, or glyoxylic acid and oxalic acid in electroreduction of oxalic acid. An aqueous Na2CO3-NaHCO3 or NaOH-Na2CO3 solution was confirmed to be the most desirable eluent. The experimental results demonstrated that the detection sensitivity is ahead of ppm grade, and the variation coefficients such as the retention time, the peak height and the peak area outperform 2%. All the recoveries of the detected substances are ranged between 97 and 103%. The method exhibits advantages of high selectivity, high sensitivity, speediness and simple apparatus requirement. Furthermore, simultaneous determination of a mixture of several substances can be achieved by the developed method, and even a neutral molecule of glyoxal can be also determined by choosing an appropriate composition and concentration of eluent.

Novel ion chromatographic stationary phases for the analysis of complex matrices

Ion chromatography (IC) has a proven track record in the determination of inorganic and organic anions and cations in complex matrices. Recently, application of IC to the separation and determination of bio-molecules such as amino acids, carbohydrates, nucleotides, proteins and peptides has also received much attention. The key to the determination of all of the above species in the most analytically challenging complex matrices is the ability to manipulate selectivity through control of stationary phase chemistry, mobile phase chemistry and the choice of detection method. This Tutorial Review summarises some of the most significant recent advances made in IC stationary phase technology. In particular, the review details stationary phases specifically designed for ion analysis in complex sample matrices, and considers in which direction future stationary phase development might proceed.

Electroosmotic flow reversal for the determination of inorganic anions by capillary electrophoresis with methanol–water buffers

Manipulation of the electroosmotic flow (EOF) is essential for achieving optimized separations of small anions by capillary electrophoresis (CE). In this work, efficient suppression or reversal of EOF is achieved upon addition of small amounts of the cationic surfactants, cetyltrimethylammonium bromide (CTAB) or didodecyldimethylammonium bromide (DDAB) to the electrophoretic buffer. Highly stable and reversed EOF are achieved using the surfactants in the presence of up to 50% MeOH. In aqueous and low methanol containing solutions (up to 30%, v/v) surface aggregation of the surfactants at the capillary wall occurs at a concentration below the critical micelle concentration (CMC). The impact of MeOH on reversed EOF is predominantly a function of the diminished zeta potential of the silica, and to a lesser extent on the CMC in the bulk solution of the surfactant. Fast baseline separation and selectivity changes for small inorganic anions are observed when mixed aqueous-organic buffers are employed. Changes in EOF, micellar properties of the surfactant and selectivity for inorganic anions upon addition of various percent of methanol are also discussed.

Non-linear calibration functions in ion chromatography with suppressed conductivity detection using hydroxide eluents

The linearity of calibration curves in ion chromatography with suppressed conductivity detection using hydroxide eluents was investigated. Theoretical calibration curves were derived for strong electrolytes and weak monobasic acids and the results compared with experimental data. At low concentrations up to 1 micromol l(-1) the autoprotolysis of water induces left-curved calibration functions even for strong electrolytes like nitrate. The experimental data are best described by a quadratic function, the differences between linear and quadratic regression being up to 10%. At higher concentrations the calibration curves for strong electrolytes are linear. Due to incomplete dissociation, the calibration curves for weak mono- and dibasic acids show a right curvature. Thus, depending on the analyte and the concentration range of interest, analysts should carefully choose between a linear and a quadratic regression function.

Advances in the determination of inorganic anions by ion chromatography

The time period covered for this review includes articles published from 1997 to 1999, with the addition of a few classic references. The purpose of the review is to include the most relevant works from each topic area of the determination of inorganic anions by ion chromatography, including new sample pretreatments, new separation methods, new detection systems and the latest applications in the field of environmental, water, foods, etc. samples. Experimental conditions such as stationary phase, eluent, detection mode, as well as matrix are summarized in a table.

Electrophoretic methods in the analysis of beverages

A review of the applications of electrophoresis to the determination of various compounds in beverage samples, namely beer, hard drinks, juice, milk, soft drinks, tea and wine, is presented.

Factors affecting selectivity of inorganic anions in capillary electrophoresis

Capillary zone electrophoretic separations of inorganic anions are largely governed by the intrinsic (infinite dilution) mobility of the anion. This in turn is a function of the hydrodynamic friction caused by the size of the ion and the dielectric friction caused by the charge density of the anion re-orienting the surrounding solvent. The influence of these factors on the mobility of anions is examined in both water and nonaqueous solvents. The influence of other experimental parameters, such as ionic strength, ion association, electroosmotic flow modifier concentration, and the addition of complexing agents such as polymeric cations, cyclodextrins, crown ethers and cryptands are also reviewed. From this discussion, some rules of thumb as to when different approaches will be most effective are drawn.

Determination of inorganic ions in food and beverages by capillary electrophoresis

A review of the applications of electrophoresis to the determination of inorganic anions (sulphate, sulphite, phosphate, nitrate, nitrite and halides) and inorganic cations (ammonium, alkali and alkaline metals and trace elements) in food and beverages is presented.