A combined isopiestic and sub-boiling distillation method for the purification of hydrofluoric acid used for ICP-MS elemental analysis

摘要

Purification of hydrofluoric acid (HF) has been achieved by the combination of isopiestic and sub-boding distillation. For better yield and purity, the collection vessel's position is optimized. The distillation assembly is made from polyethylene which is available in any chemical laboratory. Impure acid (100 mL) is placed in a 1-L HDPE container and the collection vessel (PTFE beaker) containing 25 ml, pure water is kept inside the container on a perforated stand. The whole distillation set-up is heated in a water bath at 80 degrees C. After eight hours, 35 ml, of pure HF of similar to 40% strength is obtained from 100 ml, of impure 48% HF. The production of high purity HF can be increased by increasing the volume of the feed HF. The impurities in pure acid are preconcentrated in an in situ evaporating system and determined by ICP-MS after suitable dilution. The levels of impurity are in the sub-ng/g to ng/g range and the purity of the acid is close to a commercially available pure (Suprapur(R)) grade HF with respect to Cd, Co, Cr, Cu, Ga, In, Mg, Mn, Ni, Pb, Sr, and Zn.