Analytical studies on illicit heroin. III. Auto-interference in the colorimetric determination of strychnine in illicit heroin samples.

The colorimetric determination of strychnine in illicit heroin samples, based on the reduction of strychnine followed by colour development with nitrite was checked. Interference by heroin was observed, as well as a strong interference by caffeine. It was concluded that results, based on this method, are not reliable.