Sensitive, direct procedures for simultaneous determinations of iron and copper in serum, with use of 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (nitro-PAPS) as ligand.

We developed a direct, simple, and sensitive procedure for the simultaneous colorimetric assay of iron and copper in serum, using sodium dodecyl sulfate-ascorbic acid to dissociate iron and copper from transferrin and ceruloplasmin, respectively. We also use a new water-soluble reagent, 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol disodium salt (nitro-PAPS) and thioglycolic acid to eliminate interference from copper in the measurement of iron. Within- and between-run precisions of the present method were 2.5-2.8% for iron and 1.8-4.6% for copper. The proposed method is susceptible to interference by hemoglobin and lipemia, especially for the iron assay. Linear-regression analyses of results of the proposed method with those of the bathophenanthroline method for iron and of the atomic absorption spectroscopic method for copper correlated well (r = 0.996, Sy/x = 0.73 and r = 0.959, Sy/x = 1.11, respectively).