Quantitative dc arc techniques are described for estimating thallium in two distinctly different types of geological material, granitic rocks and manganese nodules. Thallium is not normally detectable in granite with average concentration of about one ppm. A highly sensitive special procedure of direct excitation has been developed so that this element may now be estimated in granites and related rocks routinely. The thallium concentration in manganese nodules is relatively high (about 50 ppm), but interference from nickel must be drastically suppressed and sample extrusion prevented before a quantitative estimation can be carried out. Details are given of the solution to these problems using K2SO4 as the diluent.
J. P. Willis, M. Kaye, and L. H. Ahrens, "The Spectrochemical Estimation of Thallium in Granites and in Manganese Nodules," Appl. Spectrosc. 18, 84-87 (1964)