Analysis of barium and strontium in sediments by dc plasma emission spectrometry

The dc plasma arc is suited to analysis of barium and strontium in a wide range of sedimentary rock matrices, from sands, shales, and carbonates, to ferromanganese nodules. Samples containing 10 ppm to more than 3000 ppm barium and strontium were studied. Both alkali (3500 ppm lithium borate, from a preliminary fusion) and lanthanum salts (1%) in the final solution are needed to achieve freedom from systematic effects due to extreme variation in matrix. In the absence of La, neither Li, Na, K, nor Cs totally eliminated effects of Al and other constituents on emission. Silica addition to the fusion helps achieve proper flux viscosity to aid removal of fused beads from graphite crucibles. The effect of refractory-substance formers such as aluminum with calcium can be reduced or removed by selection of a portion of the arc for emission measurement. However, it was decided not to pursue this approach because of loss in analytical sensitivity and need for greater precision in optical adjustment. Analysis of standard rock samples showed generally satisfactory agreement with precision methods of analysis, and some new standard rock data are reported.