Spectrophotometric determination of ammonium ion after solvent extraction with Cryptand(2.2.2)-dithizone system.

Abstract

Ammonium ion reacts with 4, 7, 13, 16, 21, 24-hexaoxa-1, 10-diazobicyclo[8.8.8]hexacosane, Cryptand(2.2.2), to form ammonium cryptate which is quantitatively extracted into chloroform as vermilion complex with dithizone. In this work the resulting vermilion complex was utilized for the spectrophotometric determination of ammonium ion. Twenty five milliliters of an aqueous solution containing ammonium ion was shaken with 25 cm3 of chloroform containing 1.0×10-3 mol dm -3 Cryptand(2.2.2) and 4×10-5 mol dm-3 dithizone in a separatory funnel. The mixture was shaken for 10 min by a mechanical shaker. After phase separation, the absorbance of the chloroform phase at 496 nm and the pH value of the aqueous phase were measured. The extracted species had a molar absorptivity of 1.0×104 dm3 mol-1 cm-1 at the absorption maximum of 496 nm. As Na+, K+ and several heavy metals were expected to interfere with the extraction process, a distillation step was introduced to remove these metal ions. A linear calibration curve was obtained up to 1 μg cm-3, the detection limit of the present method being 0.13 μg cm-3 of ammonium ion. The relative standard deviation of the measurements was 1.4% for 0.60 μg cm-3 ammonium ion standard solution. The present method was successfully applied to the analysis of several river water samples.