Abstract
Chemical speciation has become increasingly important in environmental and industrial systems, because of the difference in properties of the different physico-chemical forms of an element. In modern environmental and industrial analysis the determination of these individual species are required over and above total elemental analysis. In particular, oxidation state speciation has become a focus area of modern analytical chemistry.
Hyphenated techniques where two or more analytical techniques are coupled, have been widely used in chemical speciation analysis. In particular, chromatographic techniques coupled with suitable detection systems have been proved to be very useful in trace element speciation. In this study, modified hyphenated techniques have been proposed for vanadium and thallium speciation.
Two main species of vanadium, V(IV) and V(V) as a redox couple are widely used in petrochemical industries for the removal of sulphur. The effectiveness of vanadium as a catalyst is dependent on the ratio of the two species. Ion chromatography with an anion exchange column as the separation system, followed by ICP-OES detection at the wavelength of 309.311 nm has been proposed for the determination of the two species. In this method, EDTA was used for the stabilization of V(IV) and for the formation of V(IV) and V(V) EDTA complexes, which can be separated readily by means of a Dionex anion exchange column (AG5 guard column). The detection limits were 0.02 mg/L for V(IV), and 0.05 mg/L for V(V). The use of an ultrasonic nebulizer can enhance the sensitivity and therefore improve detection limits to as low as 2 ƒÝg/L for both species. The method is fast, cost-effective and interference free and was successfully used in the analysis of complex industrial samples.
Thallium speciation is important because thallium species have accumulative toxicity to humans. No methods for the simultaneous separation and determination of thallium species could be found in the chemical literature. In this research, a new hyphenated method, namely HPLC coupled with ICP-OES was developed for the simultaneous separation and determination of the two thallium species, Tl(I) and Tl(III). DTPA was used in this method for stabilizing Tl(III) by formation of an anionic Tl(III)-DTPA complex. After stabilization, the two species were separated by using a Dionex cation exchange column, CG12A guard column, followed by ICP-OES detection at the wavelength of 351.924 nm. The detection limits were 0.8 mg/L and 0.1 mg/L for both species when using a V-groove nebulizer and ultrasonic nebulizer, respectively. No spectral interferences were observed. Only iodide can cause a chemical interference by forming a precipitate with Tl(I).
Prof. P.P. Coetzee