Determination of Se(IV) in natural waters by adsorptive stripping voltammetry of 5-nitropiazselenol

Materials interacting with inorganic selenium from the perspective of electrochemical sensing

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(VI) to detectable Se(IV). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials…) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

Determination of Se(IV) concentration via cathodic stripping voltammetry in the presence of Cu(II) ions and ammonium diethyl dithiophosphate

The development of a methodology for the determination of Se(IV) concentration via cathodic stripping voltammetry is described in this work. The methodology is based on the formation of copper selenide (Cu₂Se), whose reduction signal at -0.60 V has been used as an analytical response to quantify the Se(IV) concentration in solution. The novelty of our methodology is the study of this system in the presence of a ligand such as ammonium diethyl dithiophosphate (ADTTP), which forms complexes with Cu(II) and Se(IV). The results showed that the presence of ADTTP plays an important role, increasing the sensitivity of the determination by almost a factor of two compared with the methodology in the absence of the ligand. The optimized conditions were pH 1.6 (phosphoric acid, 2.0 × 10^-2 mol L^-1), C_Cu(II) = 1.5 mg L^-1, C_ADTTP = 2.0 μmol L^-1, E_acc = -0.40 V and t_acc = 45 s. The detection and the quantification limits obtained were 0.065 and 0.21 μg L^-1, respectively, and linearity was maintained up to 4.0 μg L^-1 of Se(IV). The sensitivity was 10.26 nA L μg^-1. On the other hand, the relative standard deviation for 15 replicate measurements at 1.0 μg L^-1 of Se(IV) was 1.6%. The usefulness of the method was evaluated by determining Se(IV) in two certified reference materials (TMDW and TM-28.4) with relative errors of less than 2.0%. The proposed method was successfully applied to the determination of Se(IV) in spiked tap water and in a liquid pharmaceutical formulation with satisfactory results. The developed methodology presents a low detection limit, good repeatability, selectivity and linear range. Furthermore, the sensibility of the method was achieved by applying a short accumulation time (45 s).

Selenium contaminated waters: An overview of analytical methods, treatment options and recent advances in sorption methods

Selenium is an essential trace element for many organisms, including humans, but it is bioaccumulative and toxic at higher than homeostatic levels. Both selenium deficiency and toxicity are problems around the world. Mines, coal-fired power plants, oil refineries and agriculture are important examples of anthropogenic sources, generating contaminated waters and wastewaters. For reasons of human health and ecotoxicity, selenium concentration has to be controlled in drinking-water and in wastewater, as it is a potential pollutant of water bodies. This review article provides firstly a general overview about selenium distribution, sources, chemistry, toxicity and environmental impact. Analytical techniques used for Se determination and speciation and water and wastewater treatment options are reviewed. In particular, published works on adsorption as a treatment method for Se removal from aqueous solutions are critically analyzed. Recent published literature has given particular attention to the development and search for effective adsorbents, including low-cost alternative materials. Published works mostly consist in exploratory findings and laboratory-scale experiments. Binary metal oxides and LDHs (layered double hydroxides) have presented excellent adsorption capacities for selenium species. Unconventional sorbents (algae, agricultural wastes and other biomaterials), in raw or modified forms, have also led to very interesting results with the advantage of their availability and low-cost. Some directions to be considered in future works are also suggested.

Determination of mercury and selenium in herbal medicines and hair by using a nanometer TiO2-coated quartz tube atomizer and hydride generation atomic absorption spectrometry

The nanometer TiO(2) particle was coated onto the inner wall of a T-shaped quartz tube atomizer (QTA) and then was used as a new atomizer (NT-QTA) for the determination of Hg and Se by hydride generation atomic absorption spectrometry (HGAAS). After coating 67.4 mg TiO(2) on a quartz tube, the analytical performance of NT-QTA-HGAAS was compared to conventional QTA-HGAAS and it was improved as follows: (a) the linear range of the calibration curves was expanded from 10.0-80.0 ng mL(-1) to 5.0-150.0 ng mL(-1) for Hg, and from 10.0-70.0 ng mL(-1) to 5.0-100.0 ng mL(-1) for Se; (b) the characteristic concentration of was decreased from 2.8 ng mL(-1)/1% to 1.1 ng mL(-1)/1% for Hg and from 1.2 ng mL(-1)/1% to 0.8 ng mL(-1)/1% for Se; and (c) the interference from the coexistence of As on the determination of Hg and Se could be eliminated. The achieved technique was applied for the determination of Hg and Se in herbal medicines and hair.