Electrochemical Vapor Generation Research Articles

Multielement electrochemical vapor generation system coupled with atomic fluorescence spectrometer for simultaneous measurement of trace levels of As and Hg in coastal seawater samples

BackgroundToxic elements As and Hg in coastal waters affect human health through the food chain even at trace levels. The simultaneous determination of As and Hg in seawater using electrochemical vapor generation (ECVG) with atomic fluorescence spectrometer (AFS) currently has technical bottlenecks. One is the need for a simple and efficient chemical reaction cell and corresponding parameters to generate both AsH3 and Hg vapors, and the other is a suitable preservation method of the mixed standard solutions. ResultsA novel, efficient, online ECVG device was developed and interfaced with a laboratory-built multichannel AFS. The electrolytic cell adopted Sn–Pb alloy as the cathode material to generate both AsH3 and Hg vapors by electrolysis, replacing the unstable reagent tetrahydroborate (THB) usually used in most traditional vapor generation methods. The AFS was equipped with a built-in H2 generator for fuel supply, instead of the conventional acid-THB system. A mixed standard solution of As and Hg was prepared and preserved using thiourea-ascorbic acid as a fixing agent for Hg and a prereduction agent for As(V). The method detection limits (LOD, 3σ) were 0.005 and 0.003 μg/L for As and Hg, respectively. The relative standard deviations (RSD, n = 8) of the spiked samples were 2.8 % (0.50 μg/L As) and 3.1 % (0.05 μg/L Hg), respectively. The recoveries of standard spiked seawater samples with different salinities ranged from 86.1 % to 115.3 %. SignificanceThe system has been successfully applied to the simultaneous analysis of As and Hg in the seawater samples collected from the Xiamen coastal area. The study results provide a sensitive, accurate, and efficient method to promote the development and utilization of simultaneous analysis of multielement in seawaters.

Rapid determination of Hg isotopes in low concentration water samples by flow injection-plasma electrochemical vapor generation

A new strategy for determining the Hg isotopes in low Hg concentration samples is proposed, utilizing the flow injection plasma electrochemical vapor generation (FI-PEVG) sampling technique coupled with MC-ICPMS.

Fast and highly sensitive Cd isotopic analyses in low-Cd complex samples with MC-ICPMS based on plasma electrochemical vapor generation

Cd isotopes have provided a powerful tool for better understanding Cd geochemical cycling in soil, water and biological systems. Conventional solution-based MC-ICPMS techniques used for Cd isotopic analysis typically requires time-consuming purification, which greatly limits the wide application of Cd isotope. In this work, a fast, highly sensitive and cost-effective Cd isotopic analysis method has been developed based on plasma electrochemical vapor generation (PEVG) coupled with MC-ICPMS. PEVG enhances sensitivity by more than 6 times compared with conventional pneumatic nebulization (PN) system, allowing Cd analysis to be carried out with samples as low as ∼ 13 ng. Usefully, the tolerance level for organic resin materials and matrix elements (Sn/In/Pd/Zr/Mo/Zn:Cd > 250:1) is greatly improved because of the excellent matrix separation capability inherent to PEVG. This allows simplification of the complex and time-consuming ion-exchange chromatography purification process, achieving a reduction of time by > 20 times compared to conventional two-step Cd purification process. The precision and accuracy of this method were first assessed by measuring NIST 3108 and BGEG-Cd standard under optimum conditions (δ114/110Cd of 0.00 ± 0.06‰ and −1.00 ± 0.06‰ (2sd, n = 25)). The method was also successfully applied to sensitive and fast determination of δ114/110Cd in various reference materials (soil, sediment, and basalt) and environmental samples (pyrite, galena, sphalerite, soils and tap water), validating the applicability of the proposed technique. Owing to the sensitivity, selectivity, low power, and low gas consumption of the PEVG, the proposed PEVG-MC-ICPMS technique provides a much faster and cost-effective approach for the accurate measurement of Cd isotopic compositions in low-Cd complex samples.

Highly efficient electrochemical gas reduction on a three-dimensional foam electrode: mechanism and application for the determination of hazardous mercury in complex matrix.

For the first time a nickel foam electrode (NFE) is appliedin the field of electrochemical vapor generation (EVG) to carry out the electrochemical vapor phase conversion of mercury. Systematical electrochemical and morphological research has demonstrated that the specific surface area of the NFE was several times larger than that of the metal/non-metal electrode with the same geometric size. At the same time, the 3D porous channel composed of multi-layer nickel wire ensures the full contact between reactant and interface. The evident enhancement of spectral signals on aNi electrode (283%), compared with Pt (27%) and graphite (109%), confirmed that the NFE effectively enhances the yield of mercury reduction. The NFE exhibits low limit of detection (0.017μgL-1) and awide linear range (0.2-20μgL-1) with recoveries of actual samples in the range 87.8-117% towards Hg2+. Although the NFE has no advantage in electronic transmission and catalytic performance, its excellent stability, especially anti-interference and other characteristics, is sufficient for the analysis of hazardous mercury in complex matrix including certified reference materials and real samples.

Determination of Cadmium in Water Samples by Electrochemical Hydride Generation Atomic Fluorescence Spectrometry Using Series Graphite Tubes as Electrolytic Cells under Constant Voltage.

An electrochemical vapor generation (EcHG) system to determine the cadmium content using atomic fluorescence spectrometry has been established. The EcHG system uses two serially-connected graphite tubes as two electrolysis cells and an AC to DC power wall plug adapter with the constant voltage mode as a power supply. The system did not have an ion exchange membrane and only needed a pump to transport the feed solution and waste. Under these optimized conditions, the detection limit (3σ) and the relative standard deviation were 0.05 ng mL-1 and 3.2%, respectively. The EcHG efficiency was 38.4 ± 2.2%. The proposed technique has been successfully applied to determine the cadmium in three certified reference materials for environmental water and two drinking water samples.

Increasing the sensitivity of electrochemical generation of volatile Te species

Vapor generation is a very sensitive sample introduction technique for the determination of hydride forming elements by atomic spectrometry. However, the drawback of Te determination using vapor generation methods lies in the low stability of the volatilized Te species. We report a sensitive method for the determination of Te(IV) based on electrochemical vapor generation and atomic fluorescence spectrometry. Transport losses were reduced and sensitivity of the method was improved by cooling the gas-liquid separator and by using a mix of Ar and H2 as the stripping and carrier gas. The limit of detection, repeatability and generation efficiency are 0.14 ng mL−1, 2.1% and 79%, respectively.

Highly efficient electrocatalytic vapor generation of methylmercury based on the gold particles deposited glassy carbon electrode: A typical application for sensitive mercury speciation analysis in fish samples

A gold particle deposited glassy carbon electrode (Au/GCE) was first used in electrochemical vapor generation (ECVG) technology and demonstrated to have excellent catalytic property for the electrochemical conversion process of aqueous mercury, especially for methylmercury (CH3Hg+), to gaseous mercury. Systematical research has shown that the highly consistent or distinct difference between the atomic fluorescence spectroscopy signals of CH3Hg+ and Hg2+ can be achieved by controlling the electrolytic parameters of ECVG. Hereby, a new green and accurate method for mercury speciation analysis based on the distinguishing electrochemical reaction behavior of Hg2+ and CH3Hg+ on the modified electrode was firstly established. Furthermore, electrochemical impedance spectra and the square wave voltammetry displayed that the ECVG reaction of CH3Hg+ may belong to the electrocatalytic mechanism. Under the selected conditions, the limits of detection of Hg2+ and CH3Hg+ are 5.3 ng L-1 and 4.4 ng L-1 for liquid samples and 0.53 pg mg-1 and 0.44 pg mg-1 for solid samples, respectively. The precision of the 5 measurements is less than 6% within the concentration of Hg2+ and CH3Hg+ ranging from 0.2 to 15.0 μg L-1. The accuracy and practicability of the proposed method was verified by analyzing the mercury content in the certified reference material and several fish as well as water samples.

Generation of Volatile Cadmium and Zinc Species Based on Solution Anode Glow Discharge Induced Plasma Electrochemical Processes.

In this study, a novel high efficiency vapor generation strategy was proposed on the basis of solution anode glow discharge for the determination of Cd and Zn by atomic fluorescence spectrometry. In this approach, a glow discharge microplasma was acted as a gaseous cathode to initiate the plasma electrochemical vapor generation of Cd and Zn. Cadmium/zinc ions could be converted into molecular species efficiently at the plasma-liquid interface from a supporting electrolyte (HCl, pH = 3.2). It was found that the overall efficiency of the plasma electrochemical vapor generation (PEVG) system was much higher than the conventional electrochemical hydride generation (EcHG) and HCl-KBH4 system. With no requirement for other reducing reagents, this new approach enabled us to detect Cd and Zn with detection limits as low as 0.003 μg L-1 for Cd and 0.3 μg L-1 for Zn. Good repeatability (relative standard deviation (RSD), n = 5) was 2.4% for Cd (0.1 μg L-1) and 1.7% for Zn (10 μg L-1) standard. The accuracy of the proposed method was successfully validated through analysis of cadmium in reference material of stream sediment (GBW07311), soil (GBW07401), rice (GBW10045), and zinc in a simulated water sample (GSB 07-1184-2000). Replacing a metal electrode with a plasma offers the advantage of eliminating potential interactions between the species in liquid and the electrode, which solves the issues associated with electrode encountered in conventional EcHG. The ability to initiate electrochemical vapor generation reactions at the plasma-liquid interface opens a new approach for chemical vapor generation based on interactions between plasma gas-phase electrons and solutions.

Application of chemical vapor generation in ICP-MS: A review

Chemical vapor generation (CVG) is an important sample introduction technique, and is widely used for atomic spectrometry for its enhanced sensitivity and selectivity. In the past 30 years, inductively coupled plasma mass spectrometry (ICP-MS) has become a widely used and the most sensitive instrument for (ultra-)trace element determination and elemental speciation. A review of applications of this state-of-the-art coupling of CVG and ICP-MS is presented. Discussion is focused on its applications for both element determination and speciation, including hydride generation, cold vapor generation, photochemical vapor generation, alkylation, and electrochemical vapor generation. In addition, recent studies undertaken isotope dilution calibration in CVG-ICP-MS for achieving improved accuracy and precision are summarized, and the future perspectives are discussed.

Speciation of Inorganic- and Methyl-Mercury in Biological Matrixes by Electrochemical Vapor Generation from an l-Cysteine Modified Graphite Electrode with Atomic Fluorescence Spectrometry Detection

A novel nonchromatographic speciation technique for ultratrace inorganic mercury (Hg(2+)) and methylmercury (CH(3)Hg(+)) in biological materials is developed and validated by electrolytic vapor generation (EVG) coupled with atomic fluorescence spectrometry (AFS). The studies show that CH(3)Hg(+) and Hg(2+) can be converted to Hg vapor efficiently on an l-cysteine modified graphite cathode, which has never been reported before. We observe that only Hg(2+) can be converted efficiently to Hg vapor at low current mode (0.2 A). While at high current mode (2.2 A), both CH(3)Hg(+) and Hg(2+) can be reduced efficiently. As a result, we successfully establish an exact and sensitive method based on the current control to detect mercury speciation for the first time. The factors of electrolytic conditions have been optimized, and the potential mechanism is discussed. Under the optimal conditions, the detection limits (3s) of Hg(2+) and CH(3)Hg(+) in aqueous solutions are 0.098 and 0.073 μg L(-1), respectively. The relative standard deviations for 6 replicate determinations of 2 μg L(-1) Hg are determined as 3.2% and 4.7% for Hg(2+) and CH(3)Hg(+). The accuracy of the method is verified through the analysis of certified reference materials (CRM, NRC-DORM-2), and the proposed method has been applied satisfactorily to the determination of mercury speciation in several seafood samples by calibration curve mode.

Electrochemical vapor generation of selenium species after online photolysis and reduction by UV-irradiation under nano TiO2 photocatalysis and its application to selenium speciation by HPLC coupled with atomic fluorescence spectrometry.

An online UV photolysis and UV/TiO2 photocatalysis reduction device (UV-UV/TiO2 PCRD) and an electrochemical vapor generation (ECVG) cell have been used for the first time as an interface between high-performance liquid chromatography (HPLC) and atomic fluorescence spectrometry (AFS) for selenium speciation. The newly designed ECVG cell of approximately 115 microL dead volume consists of a carbon fiber cathode and a platinum loop anode; the atomic hydrogen generated on the cathode was used to reduce selenium to vapor species for AFS determination. The noise was greatly reduced compared with that obtained by use of the UV-UV/TiO2 PCRD-KBH4-acid interface. The detection limits obtained for seleno-DL: -cystine (SeCys), selenite (Se(IV)), seleno-DL: -methionine (SeMet), and selenate (Se(VI)) were 2.1, 2.9, 4.3, and 3.5 ng mL(-1), respectively. The proposed method was successfully applied to the speciation of selenium in water-soluble extracts of garlic shoots cultured with different selenium species. The results obtained suggested that UV-UV/TiO2 PCRD-ECVG should be an effective interface between HPLC and AFS for the speciation of elements amenable to vapor generation, and is superior to methods involving KBH4.