Quantitative determination of cocaine and heroin by Fourier transform infrared spectrophotometry

Cocaine hydrochloride salt (HCl) and heroin HCl were determined quantitatively by choosing a carbonyl absorption peak as the analytical peak and measuring absorbance versus concentration in standard KBr pellets. The effect of various additives and diluents such as starch, sugars, mannitol, caffeine, and procaine was also studied. Methods were devised to correct for interference contributions based on spectral subtraction of the interfering component or subtraction of the interfering spectral contribution based on absorbance ratios with a noninterfering spectral peak. In mixtures containing both the free base and the hydrochloride salt, the most satisfactory method for determining the concentration was by area integration of the two carbonyl peaks.