An indirect determination of F by atomic absorption spectrophotometry was studied. F was precipitated as CaF
2, and Ca in CaF
2 which was separated by filtering was determined by atomic absorption analysis.
The results are as follows:
(1) The addition of excess CaCl
2 as a reagent for precipitation decreased the solubility of CaF
2 in the solution.
(2) The solution was boiled for formation of CaF
2, and CeCl
3 was added to the solution, after cooling to room temperature F
-dissolved in the solution was precipitated as CeF
3.
(3) When absorbance of Ca
2+was measured after HClO
4 dryness of CaF
2, and CeF
3, the presence of Ce
3+in CeF
3 increased absorbance of Ca
2+.
(4) The amount of F, when 20 mg or over, recovered by both Ca
2+ and Cf
3+ was about 96.5% actually, and the amount of F obtained from the absorbance of Ca
2+, which was increased by Ce
3+, was indicated twice as much as F (about 1.5%) recovered by Ce
3+, but the amount of F recovered as CaF
2 was about 95%, and as CeF
3 was about 1.5%. These values were nearly constant so that the effect of the increase of the absorbance was used in that condition for increase of value of F, and F could be determined as the recovery of about 98%.
(5) The method was successfully applied to the determination of F in the coating of the low hydrogen type of electrode, fluorides of alkaline earth metals, and cryolite.
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