Dogs can detect narcotics and explosives. How do they do sense them by sniffing?

-Karthik Gurumurthy

Dogs that are trained to detect drugs often detect  the drug decomposition products . For example, methyl benzoate is one of the products which you get as a result of partial decomposition of cocaine.  If you look at the moelcule of cocaine, it has two ester linkages. Basic organic chemistry of esters have taught us that hydrolysis of esters  produces an alcohol and carboxyl acid. These again recombine to form a new ester such as methyl benzoate. Likewise Heroin, another drug is detected by presence of acetic acid vapor. This is again a decomposition product of heroin. While synthesizing illegal drugs, volatile solvents are used such as acetone, benzene in trace amounts. The sensitivity of dogs to these solvents is often the way by which these illegal drugs are detected. Same idea for detection of explosives.