Subnanogram sensitive multimetal detector with atmospheric electrolyte cathode glow discharge
A capillary version of the atmospheric electrolyte cathode glow discharge (ELCAD) cell is described which could act as a multimetal detector for chromatographic or flow injection analysis applications. The sample that is fed into the cell is analyzed through cathode-sputtering of the electrolyte surface at the end of the capillary. In contrast to the earlier ELCAD cells having large electrolyte pool cathode of 2–3 cm diameter and 10 ml min−1 flow rate, the novel cathode flow system consists of a glass capillary of 1 mm id. This new cell has a volume of 15 µl and requires only 3.5 ml min−1 flow. Excellent discharge stability is achieved by using the “electrolyte wire” in an insulator capillary as a well defined central current route to the cathode layer of the discharge. Cathodic current density is substantially higher and the cathode fall value reaches 860 V, that is ∼50% higher than that at the large cathode pool surface. Fluctuation-dampened solution feeding provides further improvement in the position stability of the cathode layer of the plasma. Blocking of the anode glow emission in the plasma imaging optics greatly reduces the noise in the emission line intensity measurement. All these positive effects result in 0.5–1.2 ng absolute and 14–34 ppb concentration detection limits for Cd, Zn, Cu, Pb and Ni in a 37 µl injection volume.