Abstract
Fundamental studies of this subject were carried out in the following method.
A new reagent “Nen-Thorin” (2-(1, 8-dihydroxy-3, 6-disulfo-2-naphthylazo)-benzene arsonic acid) (max. absorption, 500 mμ in an aq. solution of pH 2.3) was synthesised and complex of this reagent with thorium (max. absorption, 570 mμ at pH 2.3) was studied for the determination of F (<50 γ in 50 ml). The extinctions of both Neo-Thorin and its complex with Th are sensitive towards change in pH, but remain constant between pH 2.1 and 2.4, the extinction of the complex decreasing in proportion to the amount of F-.
Common ions, including Cl-, SO42-, PO43-, Al3+, Fe3+, Ca2+, and Mg2+, interefere. Any F in the sample is distilled from an H2SO4 soln. in the presence of SiO2.
(1) By using the Thorium-Neo-Thorin method, small amounts of fluorine may be easily determined.
Color of this reagent changes from red to purple with small amounts of fluorine ion. So that the visual qualitative test for flurorine possible. Realisable limit of fluorine is 1/100 p. p. m.
(2) After the plant tissue was mixed with CaO (3% by weight of dry sample) and a small amount of water, it was evaporated to dryness and the volatile matter was expelled at 250 to 300°C and then ignited at 650°C.
Maximum recovery of fluorine was 98.5%.
(3) A small amount of fluorine in animal tissue was satisfactory determined by the same procedure as in plant tissue. Namely, the sample was calcinated with CaO in proportion of 15 to 20% by weight of dry sample, charred at 350 to 400°C and ignited at 750°C. Maximum recovery of fluorine was 98.93%.
