Sensitive, Selective Analysis of Selenium Oxoanions Using Microchip Electrophoresis with Contact Conductivity Detection

Abstract

The common selenium oxoanions selenite (SeO32–) and selenate (SeO42–) 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.

Pseudomonas moraviensissubsp. stanleyae, a bacterial endophyte of hyperaccumulatorStanleya pinnata, is capable of efficient selenite reduction to elemental selenium under aerobic conditions

“…The separation background electrolyte was recently developed to specifically target Se oxyanions with high selectivity and sensitivity (Noblitt et al . ). Detection limits are 53 and 280 nmol l −1 for selenate and selenite respectively.…”

Calibration‐free quantitation in microchip zone electrophoresis with conductivity detection

“…The average deviation was 6.2%, but there was a bias with faster migrating species deviating by larger amounts. Partial injection loading of late‐migrating species is an unlikely source of the disagreement, as the 40‐s injection time is 2.5–5.5 × longer than the calculated migration time from the reservoir to the injector, and just 30 s was previously shown to be sufficient for full injections on a similar system with slower analytes . Several potential pinched‐injection anomalies have been described previously , some of which could apply here.…”

“…The gated‐injection devices’ channel lengths (mm) were sample: 30, buffer: 15, waste: 60, separation: 72 (70 effective). The pinched‐injection microchip was identical to one previously described , except for the channel height and detection wires. Channel lengths (mm) were sample: 10, buffer: 10, waste: 30, separation: 72 (70 effective).…”

“…Analytes were 0.5–25 μM with a sulfamate (5 μM) internal standard. BGE 3 is from a selenium separation . Its composition was 42 mM nicotinic acid, 15 mM nicotinamide, 2.6 mM HEPBS, and 18 mM TDAPS.…”

Room-temperature phosphorescence probe based on Mn-doped ZnS quantum dots for the sensitive and selective detection of selenite

“…The RTP quenching response of the Mn-ZnS QDs to selenite in an aqueous solution is shown in Fig. [49][50][51] It can be seen that the proposed method showed lower detection limit than other analytical techniques. † As shown in Fig.…”