Nd-YAG laser has significantly improved upon the more widely used 266 nm laser. With this technique, agreement with solution ICP-MS is generally within the laser precision.
Volcanic glass shards from ash layers present a greater challenge due to their smaller size.
Although LA spot sizes as small as 5 are possible, data quality generally suffers below 50 . In order to improve ablation characteristics at small spot sizes, we have explored the use of He instead of Ar as the ablation gas. As reported by others, He dramatically reduces the fall-out of ejecta on the sample surface. With time, however, the He signal decays and the Ar signal grows until they converge after 550-800 pulses into the sample. This behavior may result partly because less ejecta is produced as the pit deepens.