US Patent 7820449 Test strip for creatinine determination

The present invention provides a novel test piece for creatinine measurement. The test piece includes a compound expressed by the following formula (1), a metal that forms a colored complex with the compound, and a buffer agent in a porous material. The amount of creatinine is determined by optically measuring a colored complex of the compound and the metal and evaluating the degree of inhibition of the colored complex formation by creatinine. In the formula (1), R1 represents H, SO3X, or COOX. R4 and R6 represent OH, SO3X, or COOX and may be either the same or different. R2, R3, R5, and R7 represent H, OH, Cl, Br, I, NO2, NO, or CH3 and may be either the same or different. Xs in the R1, R4, and R6 represent H, Na, K, or NH4 and may be either the same or different.