Lonophore-based lithium ion film optode realizing multiple color variations utilizing digital color analysis.

Digital color analysis (DCA), utilizing colors themselves or digital information of colors, can not only be applied to various quantitative analysis using chromaticity coordinates but can also be used to develop suitable sensors for visual colorimetry based on the characteristics of human visual perception by virtual simulations based on digital color information. To achieve a clear visual color variation for lithium ion determination, we designed and prepared a color-changeable film sensor (film optode) by the use of two kinds of lipophilic dyes, KD-C4 and KD-M11, whose colors and pKa values are different. This film sensor is a plasticized PVC membrane containing the mixture of two kinds of dyes with the lithium ionophore TTD14C4 and the lipophilic anionic additive tetrakis-[3,5-bis(trisfluoromethyl)phenyl]borate sodium salt dihydrate. The simulation of the color variation using the mixed dyes was evaluated by plotting the values on a uniform chromaticity scale diagram in a*b* coordinates, after converting the tristimulus values of each dye into its L*a*b* values. When the lithium ion concentration was actually determined by the PVC film optode containing the mixed dyes whose molecular ratio of KD-C4/KD-Ml 1 was 3:1, the hues of red --> orange --> yellow --> green --> blue could be realized in the range of 10(-6)-1 M. This observed color variation was similar to the result of the virtual simulation based on DCA.