Spectrophotometric determination of calcium in paper machine white water by sequential injection analysis

A sequential injection analysis method is developed for the determination of calcium in white water of a paper machine. The determination is based on the formation of a coloured complex between Ca2+ and o-cresolphthalein complexone, which is monitored spectrophotometrically. Parameters of the method were optimized in order to give a working range as broad as possible. A working range of 5–500 mg l−1 Ca2+ was achieved with a sample volume of 30 μ1. Preliminary tests of the method were conducted using off-line samples from different paper mills in Finland. The method developed was also tested in an on-line application at a paper mill which produces wood-containing paper grades.