The Dille–Koppanyi reagent is used as a simple spot-test to presumptively identify barbiturates. It is composed of a mixture of two solutions. Part A is 0.1 g of cobalt(II) acetate dihydrate dissolved in 100 ml of methanol mixed with 0.2 ml of glacial acetic acid. Part B made up of is 5% isopropylamine (v/v) in methanol. Two drops of A are dropped onto the substance followed by one drop of B and any change in colour is observed.
The test turns phenobarbital, pentobarbital, amobarbital and secobarbital light purple by complexation of cobalt with the barbiturate nitrogens. The test, in a slightly different formulation, was developed in the 1930s by the Hungarian-American pharmacologist Theodore Koppanyi (1901–1985) and the American Biochemist, James Madison Dille (1928–1986).
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- Koppanyi, T.; Dille, J. M.; Murphy, W. S.; Krop, S. (1934). "Studies on barbiturates. II. Contributions to methods of barbital research". Journal of the American Pharmaceutical Association. 23 (11): 1074–1079. doi:10.1002/jps.3080231103.
- Dille, J. M.; Koppanyi, T. (1934). "Studies on barbiturates. III. Chemical assay of barbiturates". Journal of the American Pharmaceutical Association. 23 (11): 1079–1084. doi:10.1002/jps.3080231104.