What is the absorbance maximum for the Jendrassik Groff method?

• A. 600 nm
• B. 560 nm
• C. 450 nm
• D. 520 nm

Answer: (A)

In colorimetric bilirubin measurement with the Jendrassik-Grof method, you aim to detect the strongest possible signal from the colored reaction product. The azobilirubin formed in this reaction has a peak absorbance at a wavelength determined by the exact reagent mix and setup. In this question’s context, that peak lies near 600 nm, so measuring absorbance there gives the greatest sensitivity and the most reliable result. Reading at wavelengths away from the peak would yield a weaker signal and can be more affected by background color or turbidity. (Note that some protocols report maxima around 540–560 nm depending on reagent formulations and instruments; always follow the specific assay instructions.)