Åke Olin

Preconcentration and separation of inorganic selenium on Dowex 1X8 prior to hydride generation—atomic absorption spectrometry

Exchange reactions between inorganic selenium species and chloride were studied on Dowex 1X8. The concentration exchange constants were determined with the batch technique at room temperature and used to predict the chromatographic enrichment and separation of tetra- and hexavalent selenium. A procedure for the determination of total selenium after digestion with permanganate and anion exchange preconcentration was also developed. The enrichment techniques were applied to the determination of Se(IV) and total dissolved selenium in drinking water and fresh water using flow injection hydride generation-atomic absorption spectrometry (HG-AAS). Results agreed with those obtained in a HG-AAS system where selenium was preconcentrated as hydrogen selenide in a trap at liquid nitrogen temperature.

Determination of total selenium in water by atomic-absorption spectrometry after hydride generation and preconcentration in a cold trap system

A cold trap system for the determination of selenium by hydride generation-atomic absorption spectrometry (HG-AAS) is described. For a 30-ml sample the limit of detection is <2 ng/l. and the precision is better than 4% at the 30 ng/l. level. A number of digestion procedures for the destruction of organic matter prior to the determination of total dissolved selenium in water has been tested and compared. Concordant results were obtained except for oxidation by peroxodisulphate in strongly acidic solutions with a high content of organic material. The selenium concentrations found were in agreement with those obtained by HG-AAS after preconcentration by evaporation and dry ashing with the magnesium nitrate-nitric acid-hydrochloric acid method.

The rate of reduction of selenium(VI) to selenium(IV) in hydrochloric acid.

The reduction of selenium(VI) to selenium(IV) in 4, 5 and 6M hydrochloric acid was studied at temperatures between 50 and 95 degrees . The reaction rate was determined by measurement of the selenium(IV) formed, by continuous-flow hydride-generation atomic-absorption spectrometry. The most notable feature of the reaction is the strong increase in rate with increasing hydrogen-ion concentration and temperature. The rate increases initially with chloride concentration at constant acidity (mixtures of hydrochloric and perchloric acid) but levels off to an almost constant value at high chloride concentrations.

Comparison of four digestion methods for the determination of selenium in bovine liver by hydride generation and atomic-absorption spectrometry in a flow system

A flow system for hydride generation and atomic-absorption spectrometry is described, and the results from the optimization of the equipment for selenium determination are reported. For a sample volume of 0.6 ml the limit of detection for selenium was 0.1 mug l . and the imprecision less than 1% RSD at the 10-mug l . level. Four digestion procedures for selenium in bovine liver have been tested. All procedures gave concordant results, provided that the standard-additions method was used. The accuracies of the overall analytical procedures were estimated by comparison with results from neutron-activation analysis and analysis of NBS Bovine Liver, No. 1577. These comparisons proved that the accuracies of the procedures described in this paper are good.

Determination of selenium in freshwaters by cathodic stripping voltammetry after UV irradiation

An analytical method was developed for the determination of total dissolved selenium in fresh waters, using linear sweep cathodic stripping voltammetry (CSV) in combination with UV photolytic digestion. Both the CSV method, based on the electrodeposition and stripping of Cu(2)Se, and the UV irradiation procedure were investigated in detail. In the presence of dissolved organic substances, as in freshwaters, Se(VI) is reduced to Se(IV) by UV irradiation in 0.1M hydrochloric acid. Glucose can be used as the carbon source in samples low in natural dissolved organic carbon (DOC). The photolytic yields of Se(IV) were about 90% in both cases. Five freshwater samples were analysed for total selenium by CSV after UV photolysis, and by hydride generation atomic absorption spectrometry (HG-AAS) after oxidative digestion followed by reduction with hydrochloric acid. The results agreed well and the concentrations were in the range 70-190 ng/l., well above the detection limit of the CSV method at 2 ng/l.

CATHODIC STRIPPING VOLTAMMETRY OF CU2SE AT MERCURY-ELECTRODES

The electrochemistry of the codeposition of Se(IV) and Cu2+ at a hanging-mercury-drop electrode has been studied in detail in 0.1 M HClO4 or HCl solutions. Films consisting of Cu2Se are formed and the cathodic stripping of these films results in a single

Equilibrium and kinetic properties of a fast iminodiacetate based chelating ion exchanger and its incorporation in a FIA-ICP-AES system

The equilibrium and kinetic properties of an iminodiacetate (IDA) based chelating ion exchanger with a crosslinked agarose, Novarose, as support has been investigated. The second and third acidity constants and some complexation constants of the ligand were determined for adsorbents with metal binding capacities of 140, 55 and 18 micromol ml(-1), respectively. The adsorbent of medium capacity showed fast adsorption and desorption of Cu(II), Cd(II), Ni(II) and Ca(II) both in the batch and column mode. It was found to be about 50 times faster than Chelex-100 (50-100 mesh) in accumulation of these metal ions in the batch mode. Studies of the adsorbent in a flow system, using a 5 mm x 6 mm i.d. column, indicated quantitative accumulation of Cu(II), Cd(II), and Ni(II) at volumetric flow rates up to 110 ml min(-1). Linear calibration curves with r > 0.999 and signal enhancement factors up to 1300 were obtained. Preconcentration by a FIA system connected to an ICP-AES instrument will make simultaneous measurement of ultratrace concentrations of a number of metal ions possible within reasonable cycle times due to the high flow rates which can be used with the adsorbent. Trace amounts of cadmium and copper in tap water were determined successfully at 60 ml min(-1). However, copper and nickel in tap water are strongly complexed and do not accumulate quantitatively even at low flow rates. Hence a sample pretreatment is needed. Copper was completely adsorbed after UV-treatment of the sample.

Solid-phase extraction procedure for the determination of selenium by capillary gas chromatography

Abstract A solid-phase extraction procedure to be used in the determination of selenium by gas chromatography with electron-capture detection (GC-ECD) was investigated. After derivatization of Se(IV) with 1,2-diamino-3,5-dibromobenzene the formed 4,6-dibromopiazselenol was adsorbed on a porous divinylbenzene polymer. Elution was performed with toluene. The proposed solid-phase extraction procedure was compared with a liquid—liquid extraction procedure and the overall efficiency was approximately 97% for sample volumes between 5 and 100 ml. Concordant results were obtained for natural water samples spiked with selenium between the GC-ECD procedure and a hydride generation atomic absorption spectrometric procedure. Removal of dissolved organic carbon in natural waters on XAD-8 and Dowex 1X8 prior to selenium determination was also studied.

Bromide concentration in Swedish precipitation, surface and ground waters

The occurrence of bromide in precipitation, surface and ground waters in Sweden has been investigated (300 samples). The concentration of bromide in precipitation is 0.05–0.15 μM in the south and <0.05 μM in the north of Sweden. The concentrations of bromide and chloride are well correlated. For river water the same areal distribution pattern as for precipitation is found, but the concentrations are 2–4 times higher. The molar ratio Br/Cl is 1 × 10−3 which is lower than that for sea water (1.54 × 10−3) and, most likely, also lower than for precipitation. A detailed study of Lake Malaren has been made. The north-eastern feeder streams, passing an area of post-glacial clay, showed unusually high bromide concentrations (0.3–3 μM) and Br/Cl quotients (2 × 10−3-8 × 10−3). No correlation between the concentrations of bromide and chloride was found. Rough calculations indicate that fertilizers and chemicals added to the fields could only contribute a minor fraction of the bromide found. Analysis of 18 ground water samples indicated increased bromide levels as compared to surface waters.

Cathodic stripping voltammetry of HgSe

Abstract The problem with the presence of several cathodic stripping peaks for HgSe in acidic Se(IV) solutions has been addressed using linear sweep, cyclic, square-wave and differential pulse stripping voltammetry at a hanging-mercury-drop electrode (HMDE). When very small amounts of selenium are accumulated, the selenium is dissolved in the HMDE and a single cathodic stripping peak is obtained. The solubility of selenium in mercury was estimated to 1–2 nmol cm −3 . The deposition of larger amounts of selenium gives rise to up to three film stripping peaks, most probably because of the reduction of thin two-dimensional and thicker three-dimensional HgSe islands formed simultaneously on the mercury surface. In the presence of Cl − , a single narrow HgSe film stripping peak is observed after deposition at a potential close to the positive potential limit of the electrode. The different voltammetric stripping techniques have been evaluated with respect to sensitivity and applicability. At low selenium concentrations, when the selenium is dissolved in the mercury electrode, square-wave or differential pulse stripping voltammetry is the method of choice. At higher concentrations, when most of the material is present as HgSe, linear sweep voltammetry is the most reliable technique.