Abstract
In this work, a new kinetic method is described for the determination of trace Se(IV) in natural spring waters and commercial tea samples. The method is based on the activation of Se(IV) onto the indicator reaction in acidic medium. The reaction was monitored using a fixed time approach of 20 min at 680 nm. The variables affecting the reaction rate were evaluated and optimized. The method allows the determination of Se(IV) in the range of 0.0125-1.0 mg L-1 with a detection limit of 3.6 µg L-1. The precision was in range of 0.63-3.15% (as RSD %) with a higher recovery than 98.6%. The method has been found to be selective against matrix effect. The method was applied to the speciation analysis of inorganic Se species present in the selected samples. The method was statistically validated by analysis of two certified samples and comparing the obtained results to those of HG-AAS analysis. Also, the total Se levels of the samples were determined by using both methods after conversion of Se(VI) into Se(IV) in ultrasonic bath in acidic medium for 30 min at 85-90 °C. The results were in good agreement with those of HG-AAS. The Se(VI) level of the samples was calculated from the difference between amounts of total Se and Se(IV).
Highlights
Selenium is an essential trace element with only a small difference between toxic and essential levels
Phosphomolybdic acid (PMA), a heteropoly acid with three acid ionization constants, is a dye which is commonly used for sensitive detection of low molecular mass compounds such as alkaloids, phenolic species and steroids for visualization of complex biological structures in TLC
Because the developed method is based on a Se-activated indicator reaction and the final intermediate product is stable for fixed time of 20 min even at a temperature of 70 °C, this detection tool can be efficiently used for the fast, accurate and reliable analysis of selenium species
Summary
Selenium is an essential trace element with only a small difference between toxic and essential levels. Selenium concentration in fresh waters is usually around 20 μg L-1. Traces of selenium ranging from 0.01 to 10 μg L-1 are commonly found in community drinking water. The guideline level of selenium in drinking water set by the World Health Organization (WHO) was 10 μg L-1 3. As bioavailability and absorption strongly depend on chemical form in which the element is present, rapid, accurate and precise analytical methodologies for the qualitative and quantitative speciation analysis of selenium in foodstuffs are becoming more and more necessary[4]. Beverages may act as another important potential ingestion way to elements in our daily life[5]. As a popular nonalcoholic and healthy beverage, tea is massively consumed in the world[6]. The regular consumption of tea may contribute to the daily
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