Capillary electrophoretic determination of selenocyanate and selenium and tellurium oxyanions in bacterial cultures

Detection of Selenocyanate in Biological Samples by HPLC with Fluorescence Detection Using König Reaction

We developed a simple and sensitive HPLC method for the determination of selenocyanate (SeCN^-). The König reaction, which is generally used for the determination of cyanide and thiocyanate, was applied for the post-column detection, and using barbituric acid as a fluorogenic reagent made it possible to detect SeCN^- with high sensitivity. The limits of detection (LOD) and quantification (LOQ) were 73.5 fmol and 245.1 fmol, respectively. Subsequently, the amounts of SeCN^- in human blood and in cultured cell samples were analyzed, and no SeCN^- was detected in human whole blood. Interestingly, we have found that some of the spiked SeCN^- decomposed to cyanide in human whole blood. Ascorbic acid suppressed the decomposition of SeCN^- to cyanide by reducing the ferric ion, which is typically involved in SeCN^- decomposition. Then, SeCN^- was detected in cultured HEK293 cells exposed to selenite. The established HPLC method with fluorescence detection of SeCN^- is useful for investigating small amounts of SeCN^- in biological samples.

Sensitive, selective analysis of selenium oxoanions using microchip electrophoresis with contact conductivity detection

The common selenium oxoanions selenite (SeO3(2-)) and selenate (SeO4(2-)) are toxic at intake levels slightly below 1 mg day(-1). These anions are currently monitored by a variety of traditional analytical techniques that are time-consuming, expensive, require large sample volumes, and/or lack portability. To address the need for a fast and inexpensive analysis of selenium oxoanions, we present the first microchip capillary zone electrophoresis (MCE) separation targeting these species in the presence of chloride, sulfate, nitrate, nitrite, chlorate, sulfamate, methanesulfonate, and fluoride, which can be simultaneously monitored. The chemistry was designed to give high selectivity in nonideal matrices. Interference from common weak acids is avoided by operating near pH 4. Separation resolution from chloride was enhanced to improve tolerance of high-salinity matrices. As a result, selenate can be quantified in the presence of up to 1.5 mM NaCl, and selenite analysis is even more robust against chloride. Using contact conductivity detection, detection limits for samples with conductivity equal to the background electrolyte are 53 nM (4.2 ppb Se) and 380 nM (30 ppb) for selenate and selenite, respectively. Analysis time, including injection, is ∼2 min. The MCE method was validated against ion chromatography (IC) using spiked samples of dilute BBL broth and slightly outperformed the IC in accuracy while requiring <10% of the analysis time. The applicability of the technique to real samples was shown by monitoring the consumption of selenite by bacteria incubated in LB broth.

Simple, fast, and sensitive method for quantification of tellurite in culture media

A fast, simple, and reliable chemical method for tellurite quantification is described. The procedure is based on the NaBH(4)-mediated reduction of TeO(3)(2-) followed by the spectrophotometric determination of elemental tellurium in solution. The method is highly reproducible, is stable at different pH values, and exhibits linearity over a broad range of tellurite concentrations.

Biological interactions of selenocyanate: bioprocessing, detection and toxicity

The selenocyanate anion, SeCN(-), has been reported in wastewater from refineries whose petroleum comes from Se-rich marine shales. A metalloid-resistant bacterium was exposed to aqueous solutions of SeCN(-) to examine the relative toxicity of SeCN(-), and the results were compared with the toxicity of selenate and selenite and another G16 metalloid oxyanion, tellurite. We also determined the volatile organo-selenium species produced by bacterial cultures amended with selenocyanate anion, and we investigated a solid phase preconcentration technique for collecting SeCN(-) from aqueous samples with different ionic strengths and subsequent detection using capillary electrophoresis. The relative toxicity of SeCN(-) is comparable to that of selenate and selenite using the metalloid-resistant bacterium LHVE as the test organism. Tellurite was more toxic at all concentrations examined than all three selenium-containing anions, SeO4(2-), SeO3(2-), SeCN(-). Live cultures of LHVE amended with 1 mM NaSeCN produced volatile organo-sulphides and organo-selenides that could be collected in headspace using a solid phase microextraction fibre. The bioprocessing, i.e. the reduction and methylation of SeCN(-), is similar to that of selenate and selenite by other metalloid-resistant bacteria. An aqueous 1.0 mM solution of SeCN(-) could be captured from solution on solid-phase extraction (SPE) cartridges using an aminopropyl-based stationary phase. Selenocyanate anions, slowly pumped into a wetted SPE cartridge, were trapped on the cartridge's solid phase and were subsequently eluted, thereby providing an increase in concentration above that of the original SeCN(-)-containing solution. Preconcentration factors of 3.9 were achieved using a mixed sodium hydroxide/methanol elution solvent and by adding NaCl to aqueous SeCN(-) before loading on the SPE cartridge.