Automatic multicommutation flow system for wide range spectrophotometric calcium determination Original Research Article

An automatic flow system based on multicommutation concept is proposed to widen the linear concentration range for spectrophotometric calcium determination. The flow network was build up with three way solenoid valves to permit implementation of different sample processing conditions in order to achieve limited, medium and large dispersion degree without modification of the manifold configuration. Dilutions were carried out by changing both sampled volume and the analytical path length or applying zone sampling approach. The software was developed to control all steps of sample processing and to allow changing the manifold configuration in order to obtain suitable sample dilution. This condition was attained with up to 3 trials. A linear response from 0.250 to 1000 mg l−1, and a detection limit of 7 μg l−1 (99.7% confidence level) were achieved. The relative standard deviation was 0.83% (n=10) or better. The sampling rate was ca. 60 h−1 and 0.27 μg of the chromogenic reagent (3,3′-bis[N,N-bis(carboxymethyl)aminomethyl]-o-cresolphthalein) was consumed per determination. The procedure was applied to calcium determination in waters, plant materials, milk, antacid tablets, fertilizers and calcareous rocks. The results were in agreement with certified values or with those obtained with flame atomic absorption spectrophotometry at a 95% confidence level.