What are the two most common chromogens used in Trinder-type glucose assays?

• A. p-aminoantipyrine and p-aminophenazone
• B. o-tolidine and tetramethylbenzidine
• C. NADH and FAD
• D. Ascorbic acid and bilirubin

Answer: (A)

In Trinder-type glucose assays, the visible color comes from a peroxidase-catalyzed reaction where hydrogen peroxide, generated from glucose, oxidizes two chromogenic substrates to form a colored product. The two chromogens used most commonly are p-aminoantipyrine (4-AAP) and p-aminophenazone (PAP). When H2O2 is present, these two compounds undergo oxidative coupling to produce a vivid quinoneimine dye, whose intensity is proportional to the amount of glucose in the sample. This paired approach gives a stable, easily measured color change suitable for spectrophotometric detection.

Other substances listed aren’t the chromogenic pair used in this glucose assay. For example, o-tolidine and tetramethylbenzidine are chromogens used in other peroxidase-based tests but not the standard Trinder glucose method; NADH and FAD are cofactors, not color-forming substrates; and ascorbic acid and bilirubin can interfere with readings rather than serve as chromogens.