The colorimetric determination of calcium in silicate minerals

Abstract

Calcium in silicate minerals is determined in alkaline solution with glyoxal bis(2-hydroxy anil). At the pH of the reaction, aluminium, present as sodium aluminate, does not interfere, and co-precipitation of calcium with magnesium and iron is prevented by adding mannitol. Fifty micrograms of calcium can be determined in the presence of 3000 µg of magnesium and 2000 µg of iron, the calibration being linear between 0 and 80 µg of calcium.