Hopkins-Cole reaction

From Wikipedia, the free encyclopedia
Jump to: navigation, search

The Hopkins-Cole reaction, also known as the glyoxylic acid reaction, is a chemical test used for detecting the presence of tryptophan in proteins.[1] A protein solution is mixed with Hopkins Cole reagent, which consists of glyoxylic acid. Concentrated sulfuric acid is slowly added to form two layers. A purple ring appears between the two layers if the test is positive for tryptophan.[2][3] Nitrites, chlorates, nitrates and excess chlorides prevent the reaction from occurring.[4]


  1. ^ R.A. Joshi (2006). Question Bank of Biochemistry. New Age International. p. 64. ISBN 978-81-224-1736-4. 
  2. ^ Debajyoti Das (1980). Biochemistry. Academic Publishers. p. 56. ISBN 978-93-80599-17-5. 
  3. ^ P. M. Swamy (2008). Laboratory Manual on Biotechnology. Rastogi Publications. p. 90. ISBN 978-81-7133-918-1. 
  4. ^ Chatterjea (1 January 2004). Textbook of Biochemistry for Dental/Nursing/Pharmacy Students. Jaypee Brothers Publishers. p. 51. ISBN 978-81-8061-204-6.