Application of Total Reflection Long Capillary Cell to Determination of Fluoride in Drinking Water

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Abstract
Colorimetric determination of fluoride ion in drinking water was done with a long capillary cell (LCC) (length:0.7-4m). When a solution whose refractive index exceeds that of the cell material (Pyrex=1.474) is put into the capillary, a wave-guide(total reflection) cell is obtained, its transmissibility to source light is independent of cell shape. Color development was based on the la-ALC method: lanthanum-alizarin complexone was added to the sample. The fluoro-lanthanum-alizarin complexone which formed was combined with N, N-diethylaniline and extracted into isoamyl alcohol. Fluoride complex extracted to isoamyl alcohol was mixed with a mixture of carbon disulfide and acetone (the final refractive index of analyte solution=1.57). Extension of cell length longer than 1m provided highly sensitive colorimetry.Enhancement of absorption was O.5-2.5×103times in magnitude by using 4m LCC. Detection limit and recovery of this method were 10ng/l and 93-104% (for 50μg/l), respectively. The present method was applied to the determination of fluoride in drinking water collected around Tokyo.