Which stopping agent is used in the Jendrassik Groff method?

• A. Ascorbic acid
• B. Sodium acetate
• C. Methanol
• D. HCl

Answer: (A)

Stopping the color development is essential in the Jendrassik–Grof bilirubin method so you can measure a stable color. The principle is that bilirubin reacts with diazotized sulfanilic acid to form a colored azobilirubin product. Once the desired color is developed, a stopping reagent terminates further color formation and stabilizes the color for accurate spectrophotometric reading.

Ascorbic acid serves this role because it is a reducing agent that rapidly neutralizes the colored azo compound, effectively halting the reaction and preventing any further development of color. This keeps the absorbance stable at the measurement wavelength.

The other substances aren’t used as stopping agents: sodium acetate mainly acts as a buffer to control pH, methanol is a solvent, and HCl is involved in the diazotization step of the reaction, not in halting it.