Potentiometric and spectrophotometric determination of calcium in the wet end of paper machines by flow injection analysis.
A spectrophotometric and a potentiometric FIA method were used to determine calcium in samples of back water from paper mills. The spectrophotometric method used the complexation reaction between calcium and o-cresolphthalein complexon. Optimum pH for the method was calculated theoretically. An ion-selective calcium electrode based on neutral carrier was used in the potentiometric method. The spectrophotometric method had a linear range between 10 and 250 ppm calcium and the potentiometric method between 10 and 300 ppm. Samples were acidified to pH 4 either before or after filtration. Total calcium was determined by a d.c. plasma emission method. Significant amounts of calcium were found to be bound both to the solid matter and to soluble complexes in the samples. The spectrophotometric method gave higher values than the potentiometric method but both of them gave lower values than the d.c. plasma emission method. Calcium concentrations in the range 30-250 ppm were found in the samples.
Nyman
J
J
Laboratory of Analytical Chemistry, Abo Akademi University SF-20500 Turku-Abo, Finland.
Ivasca
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