The Sakaguchi reaction between arginine and hypohalites in the presence of α-phenols (Fig. 1) has been extensively employed for the colorimetric determination of this amino acid  M.A Parniak, G Lange and T Viswanatha, Quantitative determination of monosubstituted guanidines: a comparative study of different procedures, J. Biochem. Biophys. Methods 7 (1983), pp. 267–276. Abstract | View Record in Scopus | Cited By in Scopus (8) and . There have been a number of modifications to the reaction for the determination of arginine to improve the color stability and sensitivity. The Sakaguchi reaction is much faster with hypobromite than with hypochlorite, but the colored product fades at a higher rate; however, this can be prevented by adding urea to remove the excess hypobromite . Although 1-naphthol was originally used as the chromogen, other phenols including 2,4-dichloro-1-naphthol , 8-quinolinol , 5-chloro-7-iodo-8-quinolinol , and thymol  (Fig. 1) have provided superior analytical figures of merit. We have found that the reaction between arginine and hypobromite is chemiluminescent , which has been used to develop an analytical procedure that is rapid, simple, and selective for arginine in the presence of other amino acids.