Spectrophotometric determination of calcium with a flow injection system

The indirect spectrophotometric determination of 0.8–7.2 ppm calcium in the presence of magnesium, phosphate and sulphate by flow injection analysis (f.i.a.) is described. The method is based on the exchange reaction between the calcium and the zinc complex of ethylene glycol-bis(2-aminoethylether)tetraacetic acid (EGTA) in the presence of 4-(2-pyridylazo)resorcinol (PAR): Ca + Zn(EGTA) + 2 PAR ? Zn(PAR)₂ + Ca(EGTA). A home-made and a commercial flow injection system with a sampling rate of 80 h^?1, are compared. Results for water samples are in good agreement with those obtained by atomic absorption spectrometry.