Use of an air/argon microwave plasma torch for the detection of tetraethyllead

A microwave plasma torch (MPT) is evaluated as an emission source for the quantitative determination of tetraethyllead. Both argon and air are explored as the central-channel (carrier) gas for the MPT, air being attractive if the MPT is to be used as a held-monitoring device or for on-line monitoring. With either carrier gas, the MPT provided detection limits in the ppt range (pg absolute if a pulsed injection technique is used), with the best sensitivity obtained with the pure-argon plasma. The best detection limits for tetraethyllead as the free lead were 0.012 ppb, competitive with the most sensitive emission-based techniques. The dynamic range of the MPT was determined to extend well beyond the upper-concentration range (linear over three orders of magnitude) of environmental importance. As a performance diagnostic, emission profiles for the MPT operated with air and with argon as the central-channel gas are compared and excitation temperatures are determined for each plasma, with iron serving as the thermometric species. (C) 1999 Elsevier Science B.V. All rights reserved.