Photochemical Vapor Generation for Colorimetric Speciation of Inorganic Selenium

Abstract

Gold nanoparticles (AuNPs) are widely used as optical probes in colorimetric detection, thanks to their high molar extinction coefficient. However, sample matrixes of high salinity or strong acidity/alkalinity often break the electrostatic repulsion of AuNPs suspension, or/and the surface functionality of AuNPs, causing strong and unfavorable interferences. Photochemical vapor generation (PVG) is an efficient technique for the sample matrix separation. Besides, it possesses distinct features of green reducing reagent, reduced interferences from concomitant elements, and direct speciation by the assistance of photocatalyst. Herein, we developed a photochemical vapor generation (PVG) method for the green and direct speciation analysis of inorganic selenium (i.e., Se(IV) and Se(VI)), by colorimetric or visual monitoring of unmodified AuNPs. The generated Se species from PVG were directed into the AuNPs solution for a reaction to take place, which produced a specific new absorption band at 600 nm for detection. The experimental parameters, including the concentration of organic acid, the sample flow rate, the concentration of AuNPs, and the flow rate of carries gas, were optimized in detail. Under optimized conditions, the limits of detection (LOD) for Se(IV) and Se(VI) were 0.007 and 0.006 μg mL −1 by UV−vis detection, respectively. It is worth mentioning that 0.08 μg mL −1 Se can induce an obvious color change, which can be directly observed with the naked eye. Relative standard deviations (RSDs) of 4.5% and 4.3% were obtained from seven replicate measurements of 0.15 μg mL −1 Se(IV) and Se(VI) standard solution, respectively. The developed assay has been successfully applied for the speciation of Se in a dietary supplement sample and environmental water samples including lake water, seawater, simulated water reference materials, and tap water.

Fabrication of functional group-rich monoliths for magnetic field-assisted in-tube solid phase microextraction of inorganic selenium species in water samples followed by online chromatographic determination

“…However, the LOD obtained in our study is lower than that obtained using DLLME-ETAAS 15 and SPE-LEP/OES, 32 and also lower than that obtained in approaches that use a UV detector. 13,16,28,33,34 In addition, our method gives a better E value than that achieved using SPME-HGAAS 31 and HF-LPME-HPLC/UV 13 processes, and is similar to those obtained in other studies. 12,15,17,27,30,32 A comparison of the data also indicates that our method requires less extraction time (including adsorption and desorption durations) than that required for SPE-LEP/OES 32 and CPE-UV/vis 16 processes, but longer than for other approaches.…”

“…It can be seen that the consumptions of sample and eluent in our method are lower than that needed in most reported approaches. 12,15,16,27,30–32,34 The linear range achieved in the current method is wider than those of ultrasound-assisted liquid phase microextraction-electrothermal atomic absorption spectrometry (UALPME-ETAAS), 12 dispersive LLME-ETAAS (DLLME-ETAAS), 15 magnetic SPE (MSPE-ETAAS), 30 SPE-hydride generation atomic fluorescence spectrometry (SPE-HGAFS), 17 SPE-liquid electrode plasma-optical emission spectrometry (SPE-LEP/OES), 32 and DLLME-UV/vis 13,28 and CPE-UV/vis spectrophotometries. 33 Typically, better sensitivity can be obtained when highly sensitive detectors such as ETAAS, HGAFS and OES are employed.…”

“…To further illustrate the features of the established approach in the analysis of Se( iv ) and Se( vi ), a comparison was made between the analytical characteristics measured using the current method and existing approaches 12,13,15–17,27,28,30–34 (Table S3†). It can be seen that the consumptions of sample and eluent in our method are lower than that needed in most reported approaches.…”

“…12,15,17,27,30,32 A comparison of the data also indicates that our method requires less extraction time (including adsorption and desorption durations) than that required for SPE-LEP/OES 32 and CPE-UV/vis 16 processes, but longer than for other approaches. 12,13,15,17,27–31,33,34 However, in the established method, the extraction step is online combined with a chromatographic quantification process. In the previous studies, the sample preparation procedure with detection step is offline.…”

Elemental Speciation Analysis in Environmental Studies: Latest Trends and Ecological Impact

“…Aside from microextraction approaches, an interesting alternative was recently presented by Ding and co-workers, based on the photochemical vapor generation of SeH 2 and its detection by UV-Vis spectroscopy after adsorption on Au nanoparticles [50]. In this case, the direct photovolatilization by addition of formic acid and UV irradiation allowed for the generation of SeH 2 from Se(IV) exclusively, whereas the addition of nano-TiO 2 allowed for the generation of the hydride from both Se(IV) and Se(VI), eliminating the need of any chemical pre-reduction stages.…”