Abstract: Disclosed herein is a novel compound which is excellent in solubility to water around a neutral range, stable in an aqueous solution state for a long period of time, and high in coloring sensitivity with a stable coloring development, and is represented by the general formula (I): ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which may be the same as or different from one another, represent lower alkyl groups, and X.sub.1 and X.sub.2 both represent --O(CH.sub.2).sub.n SO.sub.3 M in which M is a hydrogen atom, an alkali metal ion or NH.sub.4.sup.+, and n is an integer of 2-4, or either of X.sub.1 and X.sub.2 represents --O(CH.sub.2).sub.n SO.sub.3 M in whch M and n are the same meanings as given above and the other represents a hydrogen atom. This reagent is hardly susceptible of the influence of the serum components such as hemoglobin, bilirubin and so on due to its color having absorption on a longer wavelength side.

Abstract: A reduced form coenzyme can be determined by acting a peroxidase on a reduced form coenzyme in the presence of metal ions to generate hydrogen peroxide and measuring the amount of hydrogen peroxide colorimetrically.

Abstract: Peroxidic substances in a sample, e.g. one or more peroxidic substances in fats and oils or in an organic material, lipoperoxides in a living sample, etc. can be determined, directly in a sample or after extracting the lipoperoxides from a living sample with a solvent, by contacting the peroxidic substances with an oxidizable color reagent in the presence of a metallic compound produced from a metal which is able to have two or more valences to produce color, and measuring degree of coloring colorimetrically.