Abstract
The method for the quantitative analysis of fluoride anion employs a color change from purple-red to violet under the reaction of La(III)-alizarin-complexone(ALC) with the fluoride anion. We investigated the chemical species in a La(III)-alizarin-complexone(ALC) solution as well as its reaction solution with fluoride anion by using high-resolution mass spectrometry. As a result, the complexes present in a La(III)-(ALC) solution were estimated to be (La-ALC)4–6, and their structure was an annulation consisting of (La-ALC) units. In these three complexes, only the (La-ALC)4 complex reacted with fluorine ions to produce deprotonated complexes of [(La-ALC)4-H + LaF2] and [(La-ALC)4-2H + LaF]. This deprotonation of (La-ALC)4 caused the solution to vary from purple-red to violet. (La-ALC)5–6 complexes were not detected in a solution with excessive fluorine ions. This is because (La-ALC)4 decreasing with complexation with the fluorine ions is thought to be supplied from the degradation of (La-ALC)5–6. The same results were obtained in the system of Ce(III).
