Alizarine indicator paper

Plane one drop of the solution upon zireonium-alizarin-S test paper. A yellow eolour on the red paper indicates the presenee of fluoride. 

Strongly acidify about 2 ml of the fusion filtrate with glacial acetic acid, and boil until the volume is reduced to about one-half. Cool. Place one drop of the solution upon zirconium-alizarin red S test paper (2). A yellow colour on the red paper indicates the presence of fluoride. Large amounts of sulphates and phosphates may interfere with this test. 

A large number of metallochromic indicators have been proposed for the detection of the equivalence point for the titration of the rare earths with EDTA and other polydentate ligands. These include Alizarin Red, Arsenazo I, Xylenol Orange, Eriochrome Black T, and Murexide to name only a few. The structure, conditions under which these indicators can be used, possible interferences, and references to the original papers are summarized by Aladjem (1970), p. 287. 

Pipette 25 ml of 0 05M EDTA into a flask, add 100 ml of water and neutralise to congo red paper with 10 per cent sodium hydroxide solution. Add 10 ml of IM sodium acetate, 5 ml of 2M monochloracetic acid and 1 5 ml alizarin S indicator and titrate with the thorium nitrate solution to the bluish-red end-point. 

Tests for chlorine, bromine, and fluorine content in fluxes are required as per IPC-TM-650, TM 2.3.33 and TM 2.3.35. The presence of these materials cause a reduction in the SIR and can accelerate corrosion of the PCB conductors and assembly solder joints. A test for chlorine and bromine is conducted by placing a droplet of flux on a silver chromate paper, which turns yellow or white if the halides are present. Presence of fluorine is determined by adding a droplet of purple zirconium alizarin to the flux region. A change in color from purple to yellow indicates fluorine is present. 

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