RESUMO
A simple, sensitive and interference-free method was established for simultaneous determination of trace selenium and tellurium in ore samples by HG-AFS, by using nano-TiO2 immobilized on a silica gel packed microcolumn for online preconcentration. Selenium and tellurium were selectively adsorbed to the microcolumn in acidic condition and then completely eluted with 2% (m/v) NaOH solution. The experimental conditions for hydride generation, adsorption, elution and potential interference were investigated in detail. Under the optimum conditions, the detection limits of selenium and tellurium by the proposed method with 180 s sampling time were 4.0 and 3.6 ng · L(-1), with sensitivity enhancement of 20- and 13-fold compared to conventional hydride generation method, respectively. The relative standard deviation (RSD, n=5) of this method for 1 µg · L(-1) Se(IV) and Te(IV) were 0.7% and 2.3%, respectively. This method was applied to determination of selenium and tellurium in several ore samples.
RESUMO
This paper proposes a staggered array to minimize heat concentration of an LED system. The purpose of this paper is to investigate temperature distribution with and without an optimized process of an LED system in various placements by experimental and numerical methods in order to improve thermal behavior. The proposed work develops an effective method to design an LED's placement for enhanced thermal uniformity and luminous efficacy, thus decreasing thermal concentrations and temperature of the LED system. Measured and calculated temperature distribution of the LED system shows good agreement.
