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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. [ABSTRACT FROM AUTHOR]

Abstract: The analytical characteristics of a capillary design of the electrolyte cathode atmospheric glow discharge (ELCAD), operated with a W-rod anode at a discharge current of 70mA and a discharge voltage of 950V, were exploited through spatially resolved atomic absorption spectrometry (AAS) experiments. For this purpose, the ELCAD cell, placed on a platform adjustable with micrometer screws, was inserted into the optical path of a commercial line-source AAS instrument. A flow injection system was developed and applied to introduce 3mL of aqueous standards of a set of environmentally relevant metals (Ca, Cd, Cr, Cu, Na, Pb and Zn) into the plasma. The analyte atom distribution along the vertical axis of the conically-shaped ELCAD plasma (height: 3.5mm) is element specific. All the absorbance maxima are observed in the near cathode region (e.g., in the range of 0.5–1.0mm from the cathode), while the AA signal smoothly fades towards the anode. Several spectrochemical buffers (citric acid, EDTA, chlorides of Ca, Cs, La, Li, and Na) were studied for improving the sensitivity of the AAS determinations for Cr. A significant increase in the sensitivity (20%) was found only with the addition of 0.55% (m/v) La solution. The limit of detection data for Cd, Cu, Na and Zn are 3.4, 4.2, 9.2 and 0.9mgL−1, respectively. The AAS calibration curves for Cd, Cu, Na and Zn are linear up to 75, 200, 100 and 25mgL−1, respectively. [Copyright &y& Elsevier]