Chengbin Zheng

Photo-induced chemical vapor generation with formic acid for ultrasensitive atomic fluorescence spectrometric determination of mercury: potential application to mercury speciation in water

A new photochemical reaction for mercury chemical/cold vapor generation (CVG) coupled to atomic fluorescence spectrometry (AFS) is described for the speciation analysis of inorganic mercury ion (Hg2+) and organic methylmercury (MeHg) in aqueous solution. The new CVG simply uses one reagent, formic acid only, to react with Hg2+ or MeHg in aqueous solution, under room natural light (Vis) or ultraviolet irradiation (UV), for the generation of cold mercury vapor, which is subsequently detected by AFS. In the presence of the UV, both Hg2+ and MeHg can be converted to Hg0 for the determination of total mercury; and only Hg2+ can be reduced to Hg0 with the Vis, thus determining Hg2+ only. Then, the concentration of MeHg can be calculated by subtracting the Hg2+ concentration from the total mercury concentration. The optimal conditions for the best CVG efficiency are discussed, together with the interference from transition metals. There exists no significant interference from as high as 100 mg L−1 Co2+ or Ni2+, and 50 mg L−1 Cu2+ for the determination of as low as 5 μg L−1 Hg2+. The new CVG minimizes the contamination sources and avoids off-line pre-oxidation of MeHg. A simple Hg2+ standard series can be used for the calibration of both Hg2+ and MeHg, eliminating the use of more toxic and more expensive MeHg standard series. The linear dynamic ranges of the calibration curves are up to 25 μg L−1 with the UV and 300 μg L−1 with the Vis. The limit of detection is 0.003 or 0.2 μg L−1 for total mercury with the UV or Hg2+ with the Vis, respectively. The accuracy of this method was validated by determination of mercury in one certified reference water sample. The new CVG is a simple, fast, green, highly selective, and ultrasensitive yet inexpensive method for the speciation analysis of Hg2+ and MeHg. It is expected to have similar applications in other analytical atomic spectrometric techniques.

Applications of chemical vapor generation in non-tetrahydroborate media to analytical atomic spectrometry

Chemical vapor generation (CVG) using tetrahydroborate(III) remains the most popular and successful derivatization procedure enabling gaseous sample introduction into analytical atomic spectrometers that are routinely used for the determination of trace and ultratrace amounts of hydride-forming elements as well as Cd and Hg. The number of elements amenable to tetrahydroborate(III)-derivatization has recently been extensively enlarged. Despite its many obvious advantages, drawbacks remain, such as significant interferences from transition metals. Consequently, many alternative approaches have been developed to overcome these shortcomings and to further expand the suite of elements amenable to CVG for sample introduction. This article reviews these non-tetrahydroborate-based approaches, including photochemical vapor generation (photo-CVG), borane complexes CVG, alkylation based on Grignard reactions and derivatization with NaBEt4, cold vapor generation with SnCl2, halide generation, electrochemical hydride generation, oxide generation, and generation of volatile chelates. Special attention is given to two newly developed CVG approaches: photo-CVG and reduction in the presence of cyanoborohydrides.

Temperature and nano-TiO2 controlled photochemical vapor generation for inorganic selenium speciation analysis by AFS or ICP-MS without chromatographic separation

A simple yet ultrasensitive UV photochemical vapor generation (photo-CVG) is proposed for the speciation analysis of Se(IV) and Se(VI). The new photo-CVG, which is based on Se(IV) or Se(VI) reacting with an organic acid under different reaction conditions, can be coupled to AFS or ICP-MS for the speciation analysis of Se(IV) and Se(VI) in real samples such as table salt and water samples without chromatographic separation. At low temperature, only Se(IV) can be photochemically converted to selenium volatile species, and this is used for its selective determination; however, by using boiling water bath together with nano-TiO2 as a catalyst, both Se(IV) and Se(VI) can be photochemically converted to selenium volatile species, thus determining the total of Se(IV) and Se(VI). Therefore, Se(VI) concentration can be calculated from the difference between the total and Se(IV) concentration. Optimal reaction conditions and instrumental parameters are investigated; and the interferences from transition metals and other ions, as well as the photo-CVG mechanism, are discussed. The limits of detection range from 0.02 to 0.1 ng mL−1, depending on the kind of organic acid and the detector. The accuracy of the method is validated by determining Se(IV) in certified reference water sample. Real samples including commercial table salt, waste water and mineral water were successfully analyzed. This is a simple, relatively green, highly selective and sensitive, yet inexpensive method for the speciation analysis of Se(IV) and Se(VI).

Recent Advance of Hydride Generation–Analytical Atomic Spectrometry: Part I—Technique Development

Abstract Hydride generation is the most popular and widely used chemical vapor generation technique and is interesting to analytical chemists as an effective sample introduction method, especially for elemental determination and speciation analysis by analytical atomic spectrometry. The present review provides a literature survey on the hydride generation technique coupled to analytical atomic spectrometry during the past several years, covering the literature on both tetrahydroborate-based hydride generation and non-tetrahydroborate-based hydride generation techniques. Development of other related methods coupled to hydride generation for better analytical performance of analytical atomic spectrometry is included as well.

UV Photochemical vapor generation sample introduction for determination of Ni, Fe, and Se in biological tissue by isotope dilution ICPMS.

A novel, sensitive method is described for the accurate determination of Ni, Se, and Fe in biological tissues by isotope dilution inductively coupled plasma mass spectrometry (ID ICPMS) based on sample introduction arising from online UV photochemical vapor generation (UV-PVG). Volatile species of Ni, Se, and Fe were liberated from a formic acid medium following exposure to a UV source. Sensitivities were enhanced 27- to 355-fold compared to those obtained using pneumatic nebulization sample introduction. Although precision was slightly degraded (a factor of 2) with ultraviolet photochemical mediated vapor generation (UV-PVG), limits of detection (LODs) of 0.18, 1.7, and 1.0 pg g(-1) for Ni, Se, and Fe, respectively, based on an external calibration, provided 28-, 150-, and 29-fold improvements over that realized with conventional pneumatic solution nebulization. Method validation was demonstrated by determination of Ni, Se, and Fe in biological tissue certified reference materials (CRMs) TORT-2 and DORM-3. Concentrations of 2.33 +/- 0.03, 5.80 +/- 0.28, and 109 +/- 2 microg g(-1) (1SD, n = 4) and 1.31 +/- 0.04, 3.35 +/- 0.18, and 353 +/- 5 microg g(-1) (1SD, n = 4) for Ni, Se, and Fe, respectively were obtained in TORT-2 and DORM-3, in good agreement with certified values.

Recent Advance of Hydride Generation–Analytical Atomic Spectrometry: Part II—Analysis of Real Samples

Abstract: As an extended discussion of Part I, this review provides a survey of the literature about the elemental and speciation analysis of hydride-forming and non-hydride-forming elements in real samples by using hydride generation–analytical atomic spectrometry based on the recently developed technique summarized in Part I, with emphasis on the sample pretreatment methods and interference elimination.

Versatile Thin-Film Reactor for Photochemical Vapor Generation

A novel thin-film reactor is described and evaluated for its analytical performance with photochemical vapor generation (TF-PVG). The device, comprising both the generator and a gas-liquid separator, utilizes a vertical central quartz rod onto which the sample is pumped to yield a thin liquid film conducive to the rapid escape of generated hydrophobic species. The rod is housed within a concentric quartz tube through which a flow of argon carrier/stripping gas is passed to remove and transport the generated species to a detector, which in this study is an inductively coupled argon plasma optical emission spectrometer (ICP-OES). The concentric quartz tube is itself surrounded by a 78-turn 0.5 m long quartz coil low-pressure mercury discharge lamp operating at 20 W. The performance of this thin-film photoreactor was evaluated through comparison of analytical figures of merit for detection of a number of elements undergoing PVG in the presence of formic or acetic acid with those arising from conventional solution nebulization under optimized conditions. The TF-PVG reactor provided sensitivity enhancements, of 110-, 120-, 130-, 250-, 120-, 230-, 78-, 1.3-, 16-, and 32-fold for As, Sb, Bi, Se, Te, Hg, Ni, Co, Fe, and I, respectively, and detection limit enhancements of 110-, 140-, 170-, 270-, 200-, 300-, 160-, 2.7-, 50-, and 44-fold for these same elements. Vapor generation efficiencies ranged from 20-100% for this suite of analytes. The utility of this technique was demonstrated by the determination of Fe and Ni in Certified Reference Materials DORM-3 (fish protein) and DOLT-4 (dogfish liver tissue).

Sample matrix-assisted photo-induced chemical vapor generation: a reagent free green analytical method for ultrasensitive detection of mercury in wine or liquor samples

A new and unique photo-induced mercury cold/chemical vapor generation (PI-CVG), which directly uses sample matrix as a reductant, was proposed for atomic fluorescence spectrometric detection of trace mercury in wine or liquor samples. The new method was thus termed as sample matrix-assisted PI-CVG. With the ultraviolet radiation (UV), the sample matrix (ethanol) can reduce mercury compounds or ions to atomic mercury, Hg0, which is subsequently swept (by argon carrier gas) into an atomic fluorescence spectrometer for the measurements. Under the optimized experimental conditions, the LOD for mercury was found to be 70 pg mL−1 with ethanol. The standard addition method was used for the real sample analysis to achieve the reagent free goal. The proposed method features high sensitivity, simplicity (no sample pre-treatment), rapidness, freedom of reagent (the sample matrix as the reductant), cost-effectiveness, and environmental cleanness. Indeed, this is the simplest approach to generate mercury vapor from alcohol-containing samples, and it is expected to have a wide application in the analysis of wines, liquors, and the like. Also, the PI-CVG can be coupled to other analytical atomic spectrometers.

High-Yield UV-Photochemical Vapor Generation of Iron for Sample Introduction with Inductively Coupled Plasma Optical Emission Spectrometry

A novel approach to the generation of volatile iron compounds (likely the pentacarbonyl) with high efficiency is described, wherein solutions containing either Fe(2+) or Fe(3+) and low molecular weight organic acids such as formic, acetic or propionic are exposed to a UV source. An optimum generation efficiency of 60 +/- 2% was achieved in 50% formic acid at pH 2.5 with an irradiation time of 250 s by use of a 17 W low-pressure mercury grid lamp. Compared to conventional solution nebulization, sensitivity and limit of detection were improved 80- and 100-fold, respectively, at the 238.204 nm Fe II emission line. A precision of 0.75% RSD was achieved at a concentration of 100 ng/mL. Photochemical vapor generation sample introduction was used for the determination of trace iron in several environmental Certified Reference Materials, including National Research Council Canada DORM-3 fish muscle tissue, DOLT-3 and DOLT-4 fish liver tissues, and SLRS-5 river water, providing analytical results in excellent agreement with certified values based on a simple external calibration.

Dielectric Barrier Discharge in Analytical Spectrometry

Abstract Dielectric barrier discharge is a nonequilibrium plasma, and its industrial application has been on a large scale. Similarly, its prominent features of high dissociation ability at low working temperature and low power consumption, simple and adjustable configuration, ambient working conditions, and long lifetime are favorable for developing a wide array of analytical devices as well. This review addresses the basics of dielectric barrier discharge and emphasizes their analytical applications in analytical atomic spectrometry, chemiluminescence, gas chromatographic detectors, ion source for mass spectrometry, and ion mobility spectrometry with 103 references.