Chromogen-reactive-indicator preparations containing A 3,3'-di(carbonyloxy- or sulfonyloxy-group-containing) benzidine derivative chromogen

In an analytical test, color change reagent preparation comprising a chromogen-reactive-indicator, peroxidase, an oxygen-oxidoreductase specific to a particular substance to be tested and for which there exists a specific oxygen-oxidoreductase, the improvement which consists in using as the chromogen-reactive-indicator constituent of said preparation a 3,3'-disubstituted-benzidine derivative selected from (a) those having the general formula ##STR5## wherein X is the divalent carbonyloxy or sulfonyloxy group, W is hydrogen or another cation compatible with the aforesaid other ingredients of said reagent preparation, the subscript n is 0 or 1, and (i) when X is the carbonyloxy group, A is a divalent alkylene chain with from 2 to about 7 carbons, and (ii) when X is the sulfonyloxy group, n is 0 when A is the divalent alkylene chain of from 2 to about 7 carbons, and n is 1 when A is straight chain trimethylene or tetramethylene, and (b) the acid addition salts of said disubstituted benzidine derivative, compatible with the aforesaid ingredients of the chromogen-reactive-indicator, when X is the carbonyloxy group.