Simultaneous determination of free calcium, magnesium, sodium and potassium ion concentrations in simulated milk ultrafiltrate and reconstituted skim milk using the Donnan Membrane Technique

This study focused on determination of free Ca2+, Mg2+, Na+ and K+ concentrations in a series of CaCl2 solutions, simulated milk ultrafiltrate and reconstituted skim milk using a recently developed Donnan Membrane Technique (DMT). A calcium ion selective electrode was used to compare the DMT results. The study showed that the free Ca2+ concentrations measured by the DMT agreed well with calcium electrode data. Concentrations of free Ca2+, Mg2+, Na+ and K+ measured by the DMT agreed with concentrations predicted by existing ion speciation models. It is concluded that the DMT is suitable to measure various free metal ion concentrations simultaneously in complex milk-type systems.