Evaluation of Calcium Binding Capacity of Chelating Agents in Calcium Carbonate Suspension and Effects on Calcium Distribution of Calcium Chelating Agents

In this study, the binding capacity of calcium ions of sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), trisodium citrate (TSC), and potassium oxalate (PO) were evaluated, and the calcium distribution in the presence of STPP and TSPP in CaCl2 solutions (50 mmol L−1) were investigated. Under conditions simulating industrial toothpaste, the concentration of fluoride in calcium carbonate suspensions (30 g/50 g) was measured by ion chromatography to investigate the effects of chelating agents on calcium ions. Among all the chelating agents, STPP and TSPP have the highest retention rate of fluoride, indicating better calcium binding capacity. Preliminary studies were carried out in CaCl2 solutions to investigate the influence of concentration and pH on the chelating performance of STPP and TSPP. The distribution of free calcium, chelated calcium, and precipitated calcium in CaCl2 solution in the presence of STPP and TSPP were investigated to reveal two different calcium-chelation mechanisms and laws for STPP and TSPP. This work has a positive guiding significance for the stabilisation of calcium and fluoride in toothpaste formula.