Electrically heated wire-loop, in-torch vaporization sample introduction system for inductively coupled plasma atomic emission spectrometry with photodiode array detection

Abstract

A new sample introduction system that can be used for the analysis of microliter volumes of liquids by inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The system consists of an electrically heated W wire-loop which is attached to a thermocouple ceramic insulator. Ceramic and wire-loop are inserted manually into the central tube of a modified ICP torch, with the top of the wire-loop positioned about 10 cm below the plasma. An inexpensive variac, which plugs into a wall socket, is used as a power supply. This in-torch vaporization (ITV) sample introduction system was characterized using an ICP optical emission spectrometer with a photodiode array detector. In this pilot study aimed at testing the validity of the approach, spectral interference effects arising from W emission lines are documented for Be, Cu, Mn, Sc, Sr, V, Y and Zn and preliminary analytical performance characteristics using an unoptimized wire-loop/torch design are presented. Calibration curves were linear for over three orders of magnitude for Sr, Y and Be; the non-linear calibration curves obtained for Cu were attributed to contamination from the power transfer cables, for Mg to contamination from the ceramic and for Ca to airborne particles adhering to the wire-loop. As well, Au-coated W wire-loops proved to be sensitive to Hg 0-vapor in air. Precision varied between 1.9 and 4.5% (10 μl injection of single element standards) and, estimated absolute detection limits were (in pg) Zn (710), V (20), Mn (10), Y (10), Sc (9), Be (1) and Sr (0.4).