Patent ID: 8133739

Claim:
A reagent for determining lead concentration in a sample solution in the presence of calcium ions comprising (A) a water-soluble porphyrin derivative or a salt thereof represented by formula (1): wherein at least one of X 1 to X 4 represents any of the following groups: each of the rest of the group(s) represents a hydrogen atom, and R 1 represents an alkyl group, a sulfoalkyl group, a carboxyalkyl group, a hydroxyalkyl group, or a hydrogen atom; and each of R 2 and R 3 represents a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid residue, a phosphoric acid residue, or a trialkylammonium group, (B) at least one member selected from among polyacrylamide, polyvinyl alcohol, and polyethylene glycol, and (C) a calcium-ion-supplying compound.