Standards, AA, Quality Control Standard 21. Quality Control Standard 21 is a 125mL certified reference material set in a nitric acid matrix for stability. This standard is Traceable to NIST and manufactured in accordance with stringent Quality Assurance guidelines. One year Expiration. Contains: Pb 100, Mg 100, Mn 100, Mo 100, Ni 100, Se 100, Tl 100, Ti 100, V 100, Zn 100, Sb 100, As 100, Be 100, Cd 100, Ca 100, Cr 100, Co 100, Cu 100, Fe 100, Li 100, Sr 100 ug/mL