Spectral detection of terminal ring quinones

Terminal ring quinones can be detected specifically by a simple spectroscopie method involving reaction of the quinone with quinaldinium or lepidinium salts in alkaline solution. Other types of quinones and carbonyl derivatives have given negative results. 3-Ethylrhodanine can also be used as a reagent, especially for terminal ring p-quinones. All of these colorimetric procedures are amenable to quantitation.