Spectrophotometric Determination of Calcium with Dicyclohexano- 24-crown-8 and Propyl Orange by Solvent Extraction/Flow Injection Method

Calcium in water was determined by a spectrophotometric method involving flow injection coupled with solvent extraction. An ion association complex which formed between a calcium-crown complex ion and a dye anion was extracted into an organic solvent and the absorbance of the organic phase was measured after phase separation. Six derivatives of alkylaminophenylazobenzene sulfonic acid and tetrabromophenolphthalein ethylester were examined as counter anions with dicyclohexano-24-crown-8, and a mixture of benzene and chlorobenzene was examined as an extraction solvent. A suitable method for calcium determination in water was one with Propyl Orange and a (1+1 v/v) mixture of benzene and chlorobenzene. The carrier stream was distilled water, while the reagent stream was comprised of a dye anion and lithium hydroxide. The sampling rate was 20-30 per hour. The calibration graph was linear at concentrations up to 10-4M using samples of 100μl. The detection limit corresponding to a signal-to-noise ratio of 3 was 2×10-7M; the relative standard deviation was 0.99% for 10 injections of 5×10-5M calcium solution. Calcium in river water was determined satisfactorily by the proposed method.