Electrolyte Cathode Discharge Research Articles

Direct determination of ultra-trace sodium in reactor secondary coolant waters and other waters by electrolyte cathode discharge atomic emission spectrometry

A simple, rapid and sensitive method has been described for direct determination of ultra-trace sodium in reactor secondary coolant waters and other waters by electrolyte cathode discharge atomic emission spectrometer (ELCAD-AES). This method obviates the need of any sample digestion except simple dilution followed by analysis of these waters. Direct analysis of the samples for their very low level sodium is found to be feasible by ELCAD-AES with 3% v/v formic acid without going for chemical processing/treatment like evaporation of matrix or separation and pre-concentration of sodium. The 3% v/v formic acid improves the detection limit of sodium which is found to be 0.5 ng mL−1. Repeatability of the method was found to be 8% whereas the accuracy was between 10 and 20% at ultra-trace levels. As the certified reference materials for these waters are not available, the method is validated with the corresponding results determined by graphite furnace atomic absorption spectrometer (GFAAS). The proposed method is found to be useful for direct determination of trace and ultra-trace sodium in reactor coolant waters, high purity waters and in tap and ground waters. Therefore, ELCAD-AES can be an alternative analytical technique to check ultra-trace levels of sodium and quality of the coolant waters for nuclear industries.

Temporal resolved atomic emission spectroscopy on a pulsed electrolyte cathode discharge for improving the detection sensitivity of Cu

Atmospheric pressure electrolyte cathode discharge plasma presents a great potential on detecting heavy metal pollutants. In this paper, a novel microsecond pulsed electrolyte cathode discharge was generated and coupled with temporal resolved atomic emission spectra to analyze Cu element, as one of the representative heavy metals. The waveforms of voltage and current, as well as optical emission spectra of discharge were investigated, and the experimental conditions were optimized. The spatiotemporal resolved spectra of Cu I (324.8 nm), OH (A2Σ–X2Π) and N2 (C3Πu–B3Πg) were diagnosed. The spatiotemporal distributions of gas temperature and electron density were calculated by the rotational temperature of OH (A) and the Stark broadening of Hβ (486.1 nm), respectively. It was found that the optimal detection sensitivity of Cu are obtained under the conditions of HNO3 solution with 1.0 pH value, 3.0 mL/min solution flow rate, 8.5 kV pulse peak voltage, and 100 μs pulse width. The interferences of spectral line of Cu I (324.8 nm) are mainly sourced by the spectral bands of N2 (C-B) and OH (A-X), which could be reduced by the temporal resolved spectra. The limit of detection of Cu was improved from 0.217 mg/L to 0.092 mg/L by acquiring spectra only in 25–100 μs, under the optimal conditions. Furthermore, the gas temperature and electron density play important roles in the spatiotemporal evolution of discharge and the improvement of detection sensitivity for elemental analysis.

A pulsed electrolyte cathode discharge used for metal element analysis by atomic emission spectrometry

In this paper, a pulsed electrolyte cathode discharge is generated for the purpose of detecting metal elements by atomic emission spectrometry in atmospheric air. The discharge image, and the waveforms of voltage and current are obtained for studying the discharge mode. To understand the mechanisms of metal atomic excitation, the plasma temperature and the electron density of discharge are obtained by the spectra of N2 (C-B, Δν = −2) and Hβ (486.1 nm), respectively. Also, the effects of the solution pH, solution flow rate, discharge gap, and discharge voltage on the emission intensities of Cu and Fe are discussed to acquire the optimal experimental conditions. It is found that the pulsed electrolyte cathode discharge is a kind of atmospheric pressure glow discharge, and it can analyze metal elements accurately and sensitively. The gas temperature and electron density play important roles in the improvement of emission intensities of metal elements.

Direct determination of impurities in high purity chemicals by electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES)

An ELCAD-AES method was reported for direct determination of metallic impurities in different high purity chemicals such as ammonium hydroxide, hydrogen peroxide and sulphuric acid. Direct analysis of these chemicals for their impurities was found to be feasible by ELCAD-AES without going for chemical processing/treatment like dilution or evaporation of matrix. 100% solutions of NH4OH and H2O2 chemicals produced stable ELCAD plasma, whereas 0.5% solution produced stable plasma for H2SO4. As standard addition calibration method to quantify impurities in these chemicals could not be useful, an alternative aqueous calibration method was examined and found to be suitable for their quantification by ELCAD-AES. As the certified reference materials for these chemicals were not available, the ELCAD-AES results were validated with the corresponding graphite furnace atomic absorption spectrometer (GF-AAS) results for NH4OH and H2O2 whereas for sulphuric acid they were validated with inductively coupled plasma optical emission spectrometer (ICP-OES) and supplier's results. ELCAD-AES method was free from matrix related problems and did not demand for the dilution of NH4OH and H2O2. The method was found to be useful for direct determination of trace and ultra trace metallic impurities in NH4OH and H2O2 pure chemicals and also for trace impurities in H2SO4 chemicals. Repeatability and accuracy of this method were found to be <10% and between 10 and 20% respectively. Thus ELCAD-AES could be an alternative analytical, rapid and direct analysis technique to check levels of metallic impurities (i.e. metal salts) and quality of these high purity chemicals for various industries.

Determination of cadmium in Zircaloys by electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES)

Variation of the emission signal of Cd with different volume ratios of formic acid. Error values (n = 4) are standard deviation values.

Determination of major to trace level elements in Zircaloys by electrolyte cathode discharge atomic emission spectrometry using formic acid

An electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES) method using formic acid is described for the determination of major to trace level of the elements Ni, Co, Fe, Mn, Mg, Cu, Cr, Pb, Ca in Zircaloys. The influence of HCOOH and CH3COOH to improve the sensitivity of ELCAD-AES for analyte determination is investigated. Sensitivity of ELCAD-AES was significantly improved with HCOOH for the determination of these elements. 20% (v/v) HCOOH was found to produce a maximum enhancement in the sensitivity of ELCAD-AES for the analytes. With 20% (v/v) HCOOH, improved detection limits were determined for Ni (5 ng mL−1), Co (9 ng mL−1), Fe (16 ng mL−1), Mn (7 ng mL−1), Mg (5 ng mL−1), Cu (6 ng mL−1), Cr (65 ng mL−1), Pb (10 ng mL−1), and Ca (8 ng mL−1). The improvement is 2-fold for most elements, 5-fold for Pb, and essentially unchanged for Cr. The use of HCOOH enabled the direct determination of analytes in Zircaloys by ELCAD-AES. The method has been validated by determining the concentrations of analytes Ni, Co, Fe, Mn, Mg, Cu, Cr, Pb, Ca in a Zircaloy certified reference material (Zircaloy-4 NIST-360b) and also in a Zircaloy sample which was analysed by glow discharge quadrupole mass spectrometer (GD-QMS). The precision expressed as a percentage relative standard deviation of signals of multiple analyses (N = 4) of the ELCAD-AES method was found to be between 2 and 10% for major (>0.1 wt%) and minor level ( 100 μg g−1) elements and 10–15% for trace level ( 10 ng g−1) elements. Depending on the levels of the impurities the relative error in accuracy of the ELCAD-AES method was found to be between 3 and 20%.

A Critical Review of Published Data on the Gas Temperature and the Electron Density in the Electrolyte Cathode Atmospheric Glow Discharges

Electrolyte Cathode Discharge (ELCAD) spectrometry, a novel sensitive multielement direct analytical method for metal traces in aqueous solutions, was introduced in 1993 as a new sensing principle. Since then several works have tried to develop an operational mechanism for this exotic atmospheric glow plasma technique, however these attempts cannot be combined into a valid model description. In this review we summarize the conceptual and technical problems we found in this upcoming research field of direct sensors. The TG gas temperature and the ne electron density values published up to now for ELCAD are very confusing. These data were evaluated by three conditions. The first is the gas composition of the ELCAD plasma, since TG was determined from the emitted intensity of the N2 and OH bands. Secondly, since the ELCAD is an atmospheric glow discharge, thus, the obtained TG has to be close to the Te electron temperature. This can be used for the mutual validation of the received temperature data. Thirdly, as a consequence of the second condition, the values of TG and ne have to agree with the Engel-Brown approximation of the Saha-equation related to weakly ionized glow discharge plasmas. Application of non-adequate experimental methods and theoretical treatment leads to unreliable descriptions which cannot be used to optimize the detector performance.

Influence of liquid temperature on the characteristics of an atmospheric dc glow discharge using a liquid electrode with a miniature helium flow

An atmospheric dc glow discharge using a liquid cathode and an axial miniature helium flow was generated stably between a nozzle anode and an electrolyte cathode (NaCl solution) in ambient air. Under low-current operation, the typical structure of dc glow discharges, i.e. a negative glow, a Faraday dark space and positive column, was observed. With increasing discharge current, the visible negative glow became weak and was replaced by an intense yellow-light emission, which was considered to originate from sodium atoms vaporized from the electrolyte surface by local heating due to ion bombardment from the glow discharge. To examine the effect of the liquid electrode temperature on the discharge characteristics, we controlled the electrolyte cathode temperature using an injection-type cooler or heater. The intensity of the sodium emission decreased when the electrolyte cathode was cooled, while it increased when the electrolyte cathode was heated. When a pulse-modulated dc voltage was applied, the sodium emission appeared with a delay relative to the inception of discharge, while nitrogen molecular lines appeared in the emission spectra and reached their peak intensities immediately. The temperature of the liquid cathode is an important factor in controlling the plasma–liquid interaction from the discharge and in resolving the detailed mechanism of the electrolyte cathode discharge.

Determination of Elemental Constituents in Different Matrix Materials and Flow Injection Studies by the Electrolyte Cathode Glow Discharge Technique with a New Design

An open-to-air type electrolyte cathode discharge (ELCAD) has been developed with a new design. The present configuration leads to a stable plasma even at low flow rates (0.96 mL/min). Plasma fluctuations arising from the variations in the gap between solid anode and liquid cathode were eliminated by providing a V-groove to the liquid glass-capillary. Cathode (ground) connection is given to the solution at the V-groove itself. Interfaced to atomic emission spectrometry (AES), its analytical performance is evaluated. The optimized molarity of the solution is 0.2 M. The analytical response curves for Ca, Cu, Cd, Pb, Hg, Fe, and Zn demonstrated good linearity. The limit of detections of Ca, Cu, Cd, Pb, Hg, Fe, and Zn are determined to be 17, 11, 5, 45, 15, 28, and 3 ng mL(-1). At an integration time of 0.3 s, the relative standard deviation (RSD) values of the acid blank solutions are found to be less than 10% for the elements Ca, Cu, Cd, Hg, Fe, and Zn and 18% for Pb. The method is applied for the determination of the elemental constituents in different matrix materials such as tuna fish (IAEA-350), oyster tissue (NIST SRM 1566a), and coal fly ash (CFA SRM 1633b). The obtained results are in good agreement with the certified values. The accuracy is found to be between 7% and 0.6% for major to trace levels of constituent elements and the precision between 11% and 0.6%. For the injection of 100 microL of 200 ng mL(-1) mercury solution at the flow rate of 0.8 mL/min, the flow injection studies resulted in the relative standard deviation (RSD) of 8%, concentration detection limit of 10 ng/mL, and mass detection limit of 1 ng for mercury.

Spectroscopic characterization of ion and electron populations in a solution-cathode glow discharge

The ion and electron populations of a glow discharge that uses an electrolytic solution as the cathode (an electrolyte-cathode discharge or ELCAD) were investigated. This paper presents the first determinations of electron number density, ionization temperature, and degrees of ionization in the ELCAD. Spectroscopic techniques were used to keep from perturbing the plasma, a range of conditions was explored, and two regions (the negative glow and the positive column) were observed. By using the Stark broadening of the hydrogen beta line, electron number densities near 8.5 × 1014 cm−3 for the negative glow and 2.5 × 1014 cm−3 for the positive column were found. From those results and measurements of the relative strengths of Mg neutral and ionic lines, ionization temperatures of 5000 K for the negative glow and 4600 K for the positive column were calculated. From these results, the degrees of ionization and norm temperatures were estimated for a variety of elements. Analytical implications of the study are discussed.

Investigations on the element dependency of sputtering process in the electrolyte cathode atmospheric discharge

Using a coupling of ICP with a closed electrolyte cathode discharge (ELCAD) cell as nebulizer unit it was possible to observe a well defined element dependency of the cathode sputtering process on the electrolyte surface. Investigating the ICP signal ratio referred to the pneumatic nebulization, the ELCAD sputtering produces about three times higher mass transport for Al, Cr, Pb and Cd than for Mg and Cu. B, Ba and Ca have an even lower signal while Hg shows a “super-sputtering” effect, having a 17 times higher signal with ELCAD than with pneumatic nebulization. Assuming that positively charged particles are forced back to the cathode by the 107 V m−1 field in the cathode dark space these observations fit to the model of stepwise charge neutralization by hydrolysis in the vapor-phase, which process is known in mass spectrometry. The sputtering process in the ELCAD can be described with a four-zone kinematic model of the cathode dark space.

Direct solution analysis by glow discharge: electrolyte-cathode discharge spectrometry

A new glow discharge atomic emission source was developed for the direct determination of metals in aqueous solutions by applying an atmospheric glow discharge in the air gap (2–6 mm) between an electrolyte solution cathode and a W-rod anode. Cathode sputtering of the solution surface and subsequent excitations occur when the pH of the solution is below 2.5. The spectrum emitted contains the basic atomic lines of the dissolved metals from K 769.9 to Zn 213.8 nm, ion lines of Mg and Ca and strong OH, NH and N2 bands. Boiling of the cathode pole can be avoided by use of a flow-through technique. The electron temperature was found to be around 5000 K. The calibration curves of line intensities versus metal concentrations were linear in the 1–50 ppm range and showed strong positive dependence on the discharge current and on the hydrogen ion concentration of the solution. Pulse modulated operation with time-resolved signal processing promises a substantial increase in the signal-to-background ratio. The flow-through electrolyte acts as a continuously renewed cathode pole, thereby enabling the continuous direct multi-metal assay of solutions. This report is the first discussion on the analytical characteristics of electrolyte-cathode discharge (ELCAD). spectrometry as a new technique for metal monitoring in aqueous solutions.