Reduce pentavalent arsenic and inhibit the formation of SbH3.

The function of adding stannous chloride in the ancient Chua's method is:

Reducing pentavalent arsenic inhibits the formation of SbH3, forms zinc and tin, and generates H2 uniformly and continuously.

The principle of ancient Chua's arsenic determination method is:

After the sample was digested, the high-valence arsenic was reduced to trivalent arsenic by potassium iodide and stannous chloride, and then generated hydrogen arsenide with new ecological hydrogen generated by zinc particles and acid, and then generated yellow to orange spots with mercury bromide test paper.