Chromatographic Determination of Total Selenium in Biofortified Allium sp. following Piazselenol Formation and Micro-Solid-Phase Extraction

Herein, a method based on selective piazselenol formation is applied for total selenium determination in biofortified Allium species. Piazselenol is formed by reacting Se(IV) with an aromatic diamine, namely 4-nitro-1,2-phenylenediamine, in acidic medium. Samples were digested in a nitric acid/hydrogen peroxide open system, followed by selenate reduction in hydrochloric acid. Reaction conditions were optimized in terms of pH, temperature, reaction time, and other auxiliary reagents for interference removal, namely, EDTA and hydroxylamine. For the extraction of the selectively formed 4-nitro-piazselenol, micro-solid-phase extraction (μSPE) was applied, and the analysis and detection of the corresponding complex was performed by HPLC coupled with DAD. An external standard calibration curve was developed (R2 = 0.9994) with good sensitivity, and was used to calculate the total selenium content from several Allium plants material, with good intermediate precision (RSD% < 16%). The accuracy of the method was evaluated using both, a comparison with an accepted reference method from our previously published data, as well as three certified reference material with recoveries between 84–126%. The limit of detection was determined to be 0.35 μg/g (in solids) and 1.1 μg/L (in solution), while the limit of quantification was 1.07 μg/g and 3.4 μg/L (in solution). Using the proposed method, selenium content can be quickly and accurately determined in several types of samples. In addition, this study present experimental conditions for overcoming the interferences that might be encountered in selenium determination using piazselenol.

Extractive separation of selenium for atomic-absorption determination in purified sulfur

The expanding use of sulfur in medicine, science and technology has tightened the requirements for the impurity composition, including the content of selenium in sulfur. Combined extraction-atomic absorption methods have been developed to determine selenium in purified sulfur. The possibility of using thiourea derivatives such as sodium diethyldithiocarbamate and diphenylthiocarbazone for the extraction of microgram amounts of selenium from sulfuric acid solutions was studied. Optimal conditions for the extraction of selenium from sulfate solutions are determined. Two procedures for selenium separation are proposed: extraction of selenium diethyldithiocarbamate with ethyl acetate from a solution of sulfuric acid with pH 3 or extraction of selenium dithizonate with chloroform from a 5.25 – 6.0 M sulfuric acid solution. The results of the extraction-atomic absorption determination of selenium in sulfur are compared for both procedures of selenium separation. The accuracy of the selenium determination in purified sulfur is confirmed by the method of varying sample weight. The optimal temperature-time parameters for the electrothermal atomic absorption determination of selenium are determined. The limit of selenium determination is 1 × 10–5 % wt. The values of sr in the range of selenium content 2 × 10–5 — 1 × 10–4 % wt. change from 0.10 to 0.12.