Nataša Gros

Ionic composition of seawaters and derived saline solutions determined by ion chromatography and its relation to other water quality parameters

Ion chromatography (IC) presents new possibilities for assessing information about environmental samples, namely waters of various compositions, ranging from high-purity water to highly saline ones. Constant proportion between major ions present in seawater, has been assumed in the past, from which the first practical equation relating chlorinity and salinity has been developed, being later substituted by a practical salinity scale, derived from conductivity measurements relative to a standard seawater, according to internationally accepted recommended procedures. Seawaters are characterized by salinity values around 35 while derived saline solutions may present considerable changes in ionic composition, conductivity, hence on salinity. Natural and anthropogenic phenomena may introduce new issues requiring clarification for which qualitative and quantitative information from additional sources is useful, e.g. ionic composition from IC. The different ranges of concentration of major and minor species present in seawater and derived saline solutions are a challenge for the optimization of a practical methodology for composition assessment in two single IC runs, one for anions and another one for cations, which has been attained in this work. Composition of saline solutions determined by IC was critically assessed in terms of anion-cation balance and further related to conductivity and salinity measurements aiming to evaluate the quality/completeness of ion chromatographic analyses performed at preselected conditions and to search for other meaningful relations for efficient recognition/distinction between saline solutions of different types.

Performance of ion chromatography in the determination of anions and cations in various natural waters with elevated mineralization

The performance of ion chromatography in the determination of anions and cations in natural mineral waters of different composition and different total mineralization was evaluated. Up to 12 ions of the 20 usually included in extended chemical analysis of natural waters were successfully determined by ion chromatography alone. At least 98.60% and up to 99.96% of total cation composition of mineral waters was determined by ion chromatography. Hydrogen carbonate predominated in anion composition of mineral waters and was determined titrimetrically. The percentage of anions determined by ion chromatography in the remaining anion composition of mineral waters was between 98.90% and 99.96%. The agreement between total concentrations of anions and cations in individual mineral waters determined predominantly by ion chromatography is very good and the performance of ion chromatography for the basic and for the extended chemical analysis of highly mineralized water samples is very high. Method development was assisted by previously developed algorithms and appropriate experimental conditions are also discussed.

Spectrometer with microreaction chamber and tri-colour light emitting diode as a light source.

This paper describes a tri-colour light emitting diode (LED)-photoresistor (PR)-based in situ spectrometer with geometry that differs from the previously presented and allows for small volumes of test solution (350mul) and effective homogenisation of reagents. The emission maximums of the tri-colour LED (TC-LED) are at 470, 565 and 660nm. The basic measuring characteristics of the prototype were evaluated. The prototype was tested for determination of calcium in natural waters with the o-cresolphtalein complexon and was proved to be useful for real life applications. The in situ spectrometer with microreaction chamber enables the rapid optimisation of experimental conditions, as was demonstrated on the example of oxidation of alcohols with potassium dichromate. The drop-based experimental approach to the ruggedness test is fast, economic and gives reliable results with the minimum waste production. The prototype, connected to the computer, functions as a kinetic microreactor suitable also for following rapid changes. In spite of the manual addition of the initialising reagent, the data are lost only during the first 3s.

Expert system for the ion chromatographic determination of alkali and alkaline earth metals in mineral waters

Abstract The main limiting factors (the highest concentration that may be injected, the lowest concentrations that can be determined, attainable quality of results and limitations arising from the interfering effects of ions in much higher concentrations) that could prevent the successful suppressed ion chromatographic determination of lithium, sodium, ammonium, potassium, magnesium, calcium and strontium in any particular mineral water were obtained experimentally and organized into three databases supporting the operation of an expert system. The expert system permits the planning of appropriate dilutions, the prediction of suitable detector output ranges, the planning of the appropriate standard additions or concentrations of calibration solutions necessary for the successful quantitative analysis and predicts interferences for the determination of individual ions in particular real samples. The predictions of the expert system were checked experimentally on two different natural samples. All the predictions were realistic and, although very simple calculations were used by the expert system, appropriate distinction between different extents of interferences was achieved. The described expert system works well and offers significant support to the planning of the analysis of different natural mineral waters.

A new type of a spectrometric microtitration set up.

A spectrometric microtitrator was developed from a spectrometer with a microreaction chamber and a tri-colour light-emitting diode (LED) as the light source. A novel, vertical, optical geometry of the spectrometric microtitration chamber was introduced and tested. This novel geometry also required a new method for mixing the titrated solution. A laboratory-made 50mul syringe pump was used for the addition of the titration reagent. The 10-channel module for light effects, which makes possible a low-cost hardware approach to changing the titration protocols, was used for coordinating the operation of the microtitration set up. The system, with 10 channels and a regulated speed of operation, is flexible enough to allow an operator to generate different titration protocols. The performance test showed that the speed of titration-reagent addition can be regulated in the range from 0.87 to 21.8mulmin(-1). The smallest achievable volume addition is equal to 35nl. The mixing rate can be continuously regulated by an electrical pulse that initiates the mixing cycle. The quickest rate is every 1.6s, and the slowest rate is every 4.8s. The spectrometric microtitration set up was successfully tested for several different real-life spectrometric titrations, including an iodometric titration, a determination of CO(2) in deionised water, and EDTA titrations of copper(II) ions with no indicator. The volume of the examined solution can be as small as 220mul. The titration-reagent consumption is usually between 10 and 35mul. Coefficients of variation of the end point volume determination (n = 5) at different experimental conditions and different average volumes of consumed reagents (7.06, 12.17 and 22.88mul) were 2.4, 1.3 and 1.2%, respectively. The novel geometry of the spectrometric microtitration chamber proved to be useful for real-life applications.

Microdiffusion-based UV-LED spectrometric setup for determining low levels of ethanol in fruit juice.

A novel setup is described in which we combined the separation of a volatile substance from a sample with a complex matrix on the basis of a microdiffusion process with a kinetic on-line spectrometric monitoring of the reaction in the receptive medium at 365 nm. The fruit juice was selected as a model for testing the performance of the setup in real-life applications. The ethanol content in fruit juice can be considered as an indicator of the fruit-juice quality and should not exceed the regulatory limiting values. After optimising the microdiffusion process, blackcurrant, orange and two varieties of apple juice were analysed. The sample analysis lasted 15 min at 35°C. The ethanol concentrations were found to be between 0.9 and 4.0 mmol/L, and were comparable to the results obtained using the SIST:ISO 2448:1998 standard method, which is time consuming, labour intensive and requires high sample volumes. The setup can easily be adapted for determining other volatile substances in low concentrations in complicated samples of different types by introducing different chemistry and replacing the light source if the light of a different wavelength is required. The measuring characteristics of the setup were critically assessed, the main sources of uncertainty recognised and the possibilities for further improvements of the setup and the procedure considered.

Improvement of a computer program for the ion chromatographic determination of some anions in natural waters

A previous computer program for the optimum ion chromatographic determination of fluoride, chloride, bromide, sulphate, nitrite, nitrate and hydrogenphosphate in waters was applied to conductivity detection. In this work the abilities of a spectrophotometric detector especially for the determination of bromide, nitrite and nitrate at lower concentrations were systematically examined and incorporated into the program. The new program permits the planning of the analysis with UV detection, and also the prediction of the most appropriate detector for the determination of these three anions in different individual water samples.

Optimization of ion chromatography

Abstract The strategy for planning ion chromatographic separations on a Diones AS4A column was developed on the basis of the examination of the effect of NaHCO 3 , NaHCO 3 + Na 2 CO 3 and Na 2 CO 3 eluents on the retention times of chloridie, bromide, sulphate, nitrite, nitrate and hydrogenphosphate. The suppressor limitations of increasing the eluent concentration, the upper eluent concentration limits of conductivity background stabilities, the upper concentration limits above which the anions are no longer well separated and the lower limits at which peaks become too wide or asymmetric were determined. On these bases the separation of other combination of anions can also be optimized.

Simple recognition of similar samples for the ion-chromatographic determination of the main cations

In order to develop methodology for the simple recognition of samples that are very similar by ion-chromatographic analysis, 116 different Slovenian water samples, of known composition, were considered. Suitable dilutions and appropriate detector output ranges for the ion-chromatographic determination of sodium, magnesium and calcium were predicted. These data were related to data on the chemical composition of each individual water sample, expressed in mequiv.%. A triangular diagram was designed. This is a sort of ion chromatographic map that enables institutions dealing with the periodical checking of numerous different samples to recognize the most similar samples easily and allows for the very fast and efficient transition from traditional to ion chromatographic analysis. The accuracy of the predictions was checked experimentally.

Uncertainty Budget for Simultaneous Determination of Minor and Major Ions in Seawater with Ion Chromatography Confronted with Uncertainties in Concentrations of Calibration Standards

This work deals with the development and application of the detailed uncertainty budget for simultaneous determination of minor and major ions in seawater and derived saline solutions. Combination and sequence of gravimetric or/and volumetric steps involved in introducing each particular ion into stock and final combined calibration standards; cross contamination of chemicals and dilution of samples were critically assessed and their significance to the combined uncertainty was evaluated. The main uncertainty components were identified and quantified for all anions and cations determined with ion chromatography in seawater and estuary water and confronted with uncertainties associated with concentrations of ions in combined calibration standards. Similar uncertainty components reflect very differently upon different ions.