Purity enhancement of reagents is a requirement for the preparation of geological samples that are introduced into the University of Washington Thermal Ionization Mass Spectrometer. We describe production and analysis of repetitive sub-boiling distillation of laboratory reagents. Some of these techniques may be useful in the high-purity requirements associated with target making. Initial quartz-still distillation, prior to sub-boiling distillation in Teflon stills, is indicated for some reagents. Significant improvement in purity is obtained through two quartz-still distillations followed by a sub-boiling Teflon-still distillation; however, we find little further purification with additional two- or three-stage sub-boiling distillations in Teflon. For example, typical purities obtained for HCl are <0.12 parts per trillion (ppt) Rb, 1.4 ppt Sr, 0.37 ppt Nd, and 0.02 ppt Sm.