common metal ions such as na ( + ) , k ( + ) , ca ( 2+ ) , mg ( 2+ ) , al ( 3+ ) , mn ( 2+ ) and anions such as f ( - ) , cl ( - ) , no ( - ) ( 3 ) , so ( 2- ) ( 4 ) , co ( 2- ) ( 3 ) , and po ( 3- ) ( 4 ) at the 4 mug/ml level or more do not interfere , but i ( - ) or cn ( - ) must be absent .
C0003075
anions
C0016327
f