Sodium fusion test
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The sodium fusion test is used in elemental analysis for the quantitative determination of elemental halogens, nitrogen and sulfur in a sample. It was developed by J. L. Lassaigne.
[edit] Theory
When an organic compound is heated strongly with sodium, any halogens, nitrogen, and sulfur will be converted into inorganic sodium salts such as sodium halide (for halides), sodium cyanide (for nitrogen), sodium sulfide (for sulfur), and sodium thiocyanate (for sulfur and nitrogen).
These inorganic salts can subsequently be tested using the appropriate qualitative tests.
[edit] Procedure
Place a piece of clean sodium metal, about the size of a pea into an ignition tube. Add a little of the compound (50 mg or 2 - 3 drops). Heat the tube on a Bunsen flame - gently at first, allowing any distillate formed to drop back onto the molten sodium. When charring begins, heat the bottom of the tube to dull redness for about three minutes and finally plunge the tube, while still hot, into a small beaker containing cold distilled water (6 mL) and cover immediately with a clean wire gauze.
The tube shatters, releasing the contents into the water. Any residual sodium metal will react to give sodium hydroxide. Stir the mixture, boil for 1 - 2 minutes, and filter hot through a fluted paper to remove char and broken glass.
The broken glass and char are filtered off and the aqueous solution is separated into three portions and tested for halides, cyanides, sulfides, and thiocyanates using the respective tests.
