CAPACITIVELY COUPLED PLASMA WITH TIP-RING ELECTRODE GEOMETRY FOR ATOMIC-EMISSION SPECTROMETRY - ANALYTICAL PERFORMANCE AND MATRIX EFFECT OF SODIUM-CHLORIDE AND POTASSIUM-CHLORIDE

A radiofrequency (r.f.) capacitively coupled plasma of low to medium power is described and characterized for atomic emission analysis of pneumatically nebulized sample solutions. The plasma is generated at 27.12 MHz in a torch with tip-ring electrode geometry, operated at 85-275 W with argon as support gas. The r.f. discharge is obtained at the tip of a sharp platinum electrode placed inside a quartz tube, while the second electrode is a ring outside the tube. The limits of detection for Li, Cr, Ca, Pb, Fe, Cu, Mg, Hg, Cd and Zn were in the ng ml-1 to mug ml-1 range. The introduction of NaCl and KCl, in concentrations up to 500 mug ml-1 in Na or K, produces an enhanced matrix effect for most of the elements, the highest values being obtained for easily ionizable elements. The matrix effect is less intense at higher power.