Microdetermination of Thallium with ET-AAS and ICP-AES after previous preconcentration on modified silica

abstrakt

angličtina

The toxic Thallium is a relatively extended metal in the environment which fluently awoke attention to the analyst. Since the determination of Tl by ICP-AES is of limited sensitivity the TlIIICl4- in the form of ion associate with various cationic surfactants is previously preconcentrated on modified hydrofobized silica sorbent SeparonTM SGX C18 of 60 m particle size. The formation of ion associate with cationic surfactants (Carbethoxypentadecyltrimethylammonium bromide - Septonex , benzyl-dimethyldodecylammonium bromide - Ajatin and benzyldimethyl-tetradecylammonium chloride - Zephyramine ) was tested and various ion interaction mechanisms were assumed during the sorption process.The sorption till 20 g of Tl (III) was successful from 50 -1000 ml of aqueous solutions in presence of 0,1M HCl. The subsequent elution with 96% ethanol was quantitative. Ethanol was partly evaporated under an infra-red lamp in the presence of HCl. The remaining solution was filled up to 10 mL in a volumetric flask and finally analyzed by the ICP-AES at 190,86 nm. No interference by large amounts of Cl- 500 excess of SO42-, NO3-, Ca2+, Mg2+ and K+, 100 excess of Fe3+ and Al3+ was observed. This procedure was used for the determination of Thallium in surface and mineral waters. The activation of the sorbent was provided with 0,005M Zephyramin in presence of 0,1M HCl. Samples were filtrated and degassed and a similar procedure used as before. The calibration plot was made from spikes of 1, 3 and 5 mg Tl/L and 0,5, 2 and 4 mg Tl/L spikes analysed after sorption in triplicate. The recovery of 97 - 99 % Tl was again observed. The presence of macrokomponents and microcomponents in waters was without influence on the sorption but considerable changed the calibration plots. The ET-AAS at 276,8 nm was also suitable for the direct determination of 1 - 10 g Tl. However, the volatility of Thallium at increased temperature especially in the presence of chloride is a considerable disadvantage when using ET-AAS. A number of modifiers have been tested under them PdMg(NO3)4, PdNH4(NO3)4, Pd(NO3)2, ascorbic acid and ammonium vanadate with their influence on the slopes of calibration plots for Thallium at the resonance line at 276.8 nm. The largest plot of the calibration line observed for PdMg(NO3)4 for which the blank values reaches zero. Moreover, the best temperature program for the instrument corresponded for the drying at 90 -110 centrigrade degree (20 s), charring at 700 centrigrade degree (10 s) and the atomisation at 1500 centrigrade degree (3 s) in presence 100 excess Cl-, SO42-, NO3-, Ca2+, Mg2+, Na+ and K+, as well as 100 excess of Fe3+ and Al3+. The Zeeman correction was used for the elimination of the background. In this case Thallium has been determined in urine and spruce needles according to the standard addition method.

Thallium, ICP-AES, modified silica

URBÁNKOVÁ, K.; SOMMER, L.

6. 12. 2006

Brno

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