The flame-photometric determination of calcium in solutions of high sodium content

Abstract

A method is describeds for the flame-photometric determination of 0 to 50 p.p.m. of calcium in solutions containing 4 per cent. w/w of sodium. Calcium is adsorbed from 100 ml of solution on a column of sodium-form Chelex-100 chelating resin; sodium is selectively eluted with hydrochloric acid at pH 2·4. Adsorbed calcium is eluted with 2 N hydrochloric acid and the resin washed with distilled water. The eluate and washings are diluted to 100 ml and the calcium determined on a Unicam SP900 flame photometer.

Magnesium, zinc, nickel, barium, mercury, manganese, copper and iron, present separately in concentrations of 25 p.p.m. or collectively in concentrations of 5 p.p.m. each, do not interfere. Aluminium depresses the amount of calcium found.

The method has been used to determine calcium in simulated sea water.