“…Ion exchange can be used as a basis for separating desired constituents from matrix elements which may interfere with estimation of the constituents by convenient techniques. Such elements as titanium, vanadium, molybdenum, rare earths, and gallium have been separated in this manner (1, 20, 69,110, 124, HI)• Solvent extraction for separation of metals has been used to an increased extent (41,74,105,156,157,169,172).…”