Separation of microamounts of fluoride coexisting with large amounts of aluminium and silica by improved trimethylsilylating distillation

The previously reported distillation method for the separation of fluoride as trimethyl- fluorosilane is much improved. When hexamethyldisilazane serves as the silylating agent, interference of silica can be avoided and distillation is rapid at room temperature. Aluminum is effectively masked by pyrophosphoric acid. Almost all ions tested can be tolerated in 1000-fold molar amounts to fluoride. Over 98% recovery is obtained for 49 μg of fluoride in the presence of 80 mg of aluminum plus 200 mg of silica. Concentration of fluoride from very dilute (μg l^-1) solutions is easily achieved. Satisfactory results were obtained for standard rocks.