Characterization of Chemical Species in Lanthanide (III)-Alizarin Complexone (ALC)-Fluoride Solution Using ESI-MS

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).