DETERMINATION OF CALCIUM IN WATER, URINE AND PHARMACEUTICAL SAMPLES BY SEQUENTIAL INJECTION-ANALYSIS

A sequential injection analysis system for the determination of calciu m in water, urine and pharmaceutical samples is proposed. The method i s based on the fast complexation reaction between cresolphthalein comp lexone and calcium with spectrophotometric detection. Baseline shift d ue to a background originating from coloured free reagent species, was eliminated by an optimised sequence of samples and reagents. The prop osed system is fully computerised and is able to monitor calcium in sa mples at a frequency of 43 samples per hour with a relative standard d eviation of <1.4%. The calibration graph is linear between 0 and 20 mg l(-1). The detection limit is 0.05 mg l(-1).