21 C.F.R. § 172.399
Zinc methionine sulfate, CAS Reg. No. 56329-42-1, may be safely used in accordance with the following prescribed conditions:
(b) The additive meets the following specifications:
Zinc content—19 to 22 percent. C5H11NO2S “DL-methionine”—46 to 50 percent. Cadmium—not more than 0.05 part per million.
[46 FR 58297, Dec. 1, 1981]