Multi-commutated flow system for inorganic selenium speciation in infusion tea samples by chemical vapor generation atomic fluorescence spectrometry.

This work proposes an automated strategy for the inorganic selenium speciation in infusion tea samples, employing an MSFIA-CVG-AFS system and sodium tetrahydroborate for chemical vapor generation. The selenium total is determined after an online prereduction step of selenium (VI) to selenium (IV) in alkaline media, using a UV reactor with a 15 W Hg lamp. Selenium (IV) is quantified directly on the sample, and selenium (VI) is determined by the difference between the total selenium and selenium (IV) concentrations. The optimization of the chemical parameters: hydrochloric acid - hydrobromide acid solution concentration, potassium iodide concentration, sodium hydroxide concentration, and sodium tetrahydroborate concentration was performed using a (24-1) two-level fractional factorial design. The validation parameters were determined for total selenium and selenium (IV), and the results found were: limits of detection and quantification of 0.05 and 0.18 µg L-1, respectively; a linear range of 0.18-5.0 µg L-1, precision expressed as the relative standard deviation of 2.1% for a sample number of 10, for both analytes. The system allows the speciation analysis with an injection throughput of 15 injections per hour. This analytical method was applied for inorganic selenium speciation in nine infusions of tea samples purchased commercially in supermarkets in Palma de Mallorca City, Spain. The concentrations of selenium (IV) and total selenium varied from 0.2 to 0.6 µg L-1 and 0.4-2.0 µg L-1, respectively. The accuracy method was evaluated using spike tests, and the recoveries achieved varied from 91 to 111%.

Chip-Based Spectrofluorimetric Determination of Iodine in a Multi-Syringe Flow Platform with and without In-Line Digestion-Application to Salt, Pharmaceuticals, and Algae Samples.

In this work, a flow-based spectrofluorimetric method for iodine determination was developed. The system consisted of a miniaturized chip-based flow manifold for solutions handling and with integrated spectrofluorimetric detection. A multi-syringe module was used as a liquid driver. Iodide was quantified from its catalytic effect on the redox reaction between Ce(IV) and As(III), based on the Sandell-Kolthoff reaction. The method was applied for the determination of iodine in salt, pharmaceuticals, supplement pills, and seaweed samples without off-line pre-treatment. An in-line oxidation process, aided by UV radiation, was implemented to analyse some samples (supplement pills and seaweed samples) to eliminate interferences and release iodine from organo-iodine compounds. This feature, combined with the fluorometric reaction, makes this method simpler, faster, and more sensitive than the classic approach of the Sandell-Kolthoff reaction. The method allowed iodine to be determined within a range of 0.20-4.0 µmol L-1, with or without the in-line UV digestion, with a limit of detection of 0.028 µmol L-1 and 0.025 µmol L-1, respectively.