ELECTROTHERMAL VAPORIZATION USING A TUNGSTEN FURNACE FOR THE DETERMINATION OF RARE-EARTH ELEMENTS BY INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

In electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) using a tungsten furnace, the effect of vaporizing parameters on signals and the performance of the ETV technique in the measurement of rare-earth elements (REEs) have been investigated. A mixture of argon and hydrogen was used as the carrier gas to transport sample materials to the ICP. In a transient signal observed, the signal appearance time and the peak time of oxide ions (MO+) were earlier than those of singly charged element ions (M+). The MO+/M+ ratio reached the minimum at an argon gas flow rate of 1.0 L min-1. Also, it increased as the heating temperature of the furnace rose, though the rate of increasing decreased with increasing hydrogen gas flow rate. The ratios for 11 REEs tested were in a range 10(-3) to 10(-5), 2 or 3 orders of magnitude smaller than those obtained by the conventional nebulization technique (NEB-ICP-MS). The precision for La was 1-2% at absolute amounts above 1 pg. The detection limits for 14 REEs were 0.0001-0.0006 ng mL-1, 1 order of magnitude better than those obtained by NEB-ICP-MS.