Separation and Determination of Fluoride Ion at ppb Level in the Presence of Large Excess of Al(III) and Fe(III) by Using Sapphyrin

Masaaki TABATA, Tadayuki YAMADA, Jun NISHIMOTO
2002
Fluoride ion as low as 10 -6 mol dm -3 was determined by using [2,23-diethyl-8,17-bis(2-ethoxycarbonyl)-3,7,12,13,18,22hexamethylsappyrin (H 3 sap, sapphyrin)] in the presence of large excess of aluminum(III) and iron(III), and the fluoride-sapphyrin complexes were also extracted into chloroform with nitrate ion. The formation of the ion-pair complex of fluoride ion with the sapphyrin is given as H 5 sap 2+ + F -= (H 5 sap)F + at pH 1-4.3 and the equilibrium constant is 4.84±0.05 in logarithms.
more » ... 0.05 in logarithms. The extraction equilibrium of the fluoride sapphyrin complex is written as (F -) a + (H 5 sap 3+ ·2NO 3 -) o = (H 5 sap 3+ ·F -·NO 3 -) o + (NO 3 -) a and the extraction constant is 3.66±0.01 in logarithms at 25 ºC and I = 0.1 mol dm -3 (NaNO 3 ), where the subscripts a and o denote the chemical species of aqueous and organic phases, respectively. The fluoride-sapphyrin complex gives enlarged fluorescence intensity at 680 nm on excitation 450 nm. The present method is free from the interference of a 200-fold amount of aluminum(III) and a 2000-fold amount of iron(III) for the determination and separation of fluoride ion as low as 5x10 -7 mol dm -3 in the presence of 1,2-diaminocyclehexane-N,N,N',N'-tetraacetic acid. The present method was applied to determination of fluoride ion in various water samples (tap water, river water, rain water, underground water and hot spring water).
doi:10.14891/analscisp.17icas.0.i599.0 fatcat:4tqyv5nuvzcerl3ofisvc44uhq