Study On The Binding Capacity Of Chelating Agents To Calcium Ion And The Chelating Process Of Polyphosphates

Fluoride ion with remineralization function is the main active ingredient in toothpaste to play the role of anti-caries.However,fluoride ion is prone to produce calcium fluoride precipitation in calcium carbonate toothpaste,which significantly reduces the fluoride ion content.In this paper,the effect of different chelating agents on the retention percentage of fluoride ion was studied under the condition of simulating industrial production of calcium carbonate toothpaste,and a new method to solve the above problems was provided.The traditional chelating capacity determination method is harsh and not accurate enough.In this paper,the effect of chelating agent concentration and p H on chelating ability and process were investigated without the need to separate chelated products.The specific content of this research is as follows:The calcium carbonate suspension was used to simulate the production conditions of industrial calcium carbonate toothpaste,and the effects of sodium pyrophosphate,sodium tripolyphosphate,sodium citrate,sodium gluconate and potassium oxalate and their concentrations on the retention percentage of fluoride ion and the concentration of free calcium ion were studied.The results show that,compared with the blank sample,the chelating agent has a greater improvement in the retention rate of fluoride ions and a stronger inhibitory effect on the activity of calcium ions.The binding capacity of calcium ions is in the following order:sodium pyrophosphate>sodium tripolyphosphate>potassium oxalate>sodium citrate>sodium gluconate.The calcium chelation process of sodium tripolyphosphate was studied by using calcium chloride solution as calcium source.The effects of concentration and p H of sodium tripolyphosphate solution on different forms of calcium in calcium chloride solution were investigated by combining measurement and calculation.The results show that sodium tripolyphosphate can rapidly reduce the concentration of free calcium ion and transform it into precipitation.When sodium tripolyphosphate is excessive,the precipitate gradually dissolves and forms soluble calcium-tripolyphosphate chelate,and the higher the p H,the higher the content of the chelate.Based on the experimental results,the solubility product of the precipitate was calculated to be 4.92×10^-33 and the stability constant of the chelate was 4.22×10⁶,which filled the blank of experimental data.The process of calcium chelation was studied with sodium pyrophosphate as chelating agent.The effects of concentration and p H of sodium pyrophosphate solution on the distribution of calcium species in calcium chloride solution were investigated.The results show that there are both precipitation and chelation reactions in the reaction of sodium pyrophosphate with calcium ion,but the content of chelated calcium is much less than that of precipitated calcium,and p H has little effect on this process.The characterization of the precipitates show that the concentration of sodium pyrophosphate has significant effects on the structure of the precipitates.Based on the experimental results,the solubility product of the precipitate was calculated to be8.76×10^-16 and the stability constant of the chelate were was 8.85×10⁴.