Infrared Method for Distinguishing Optical Isomers of Amphetamine James A. Heagy U.S.Bureau of Narcotics and Dangerous Drugs, Box 3607.5, 4.50 Golden Gate Ave., San Francisco, Calif. 94102 EXPERIMENTAL
THENECESSITY to identify optically active drugs occurs frequently in forensic science. Quite often such drugs are identified as to the basic drug in question without determining the optical sign and indeed many drugs are found in both licit and illicit markets as only one isomer. Amphetamine and some other drugs, however, occur in the drug trade as d-, dl-, and I-isomers. A simple microcrystalline test ( I ) will distinguish dl-amphetamine from the d- or I-isomers but cannot distinguish d- from I-. The d- or I-isomers are distinguished by mixing the sample with the proper proportion of standard dor [-amphetamine and observing a positive test for dl-amphetamine. The polarimeter will, of course, distinguish the isomers but this instrument is not available in many labora-
A water solution of any amphetamine salt (10-50 mg) is made basic and the amphetamine extracted into methylene chloride. The methylene chloride is passed through anhydrous sodium sulfate into a small beaker and concentrated to ea. 2 ml by heating on a steam bath. A saturated solution of d-mandelic acid in methylene chloride is added several drops at a time until the amphetamine is neutralized as determined by a drop of solution on pH paper. The beaker is then covered for several minutes, allowing the d-mandelate salt to crystallize and the solution is filtered using suction and the crystals washed with a small portion of methylene chloride. After drying, a KBr disk of the crystals is prepared and the infrared spectra are run.
I
I
d- amphe tamine d-mandelate
\
h
d I- amphetamine d-mandelate
P
O
0
I- amphetamine d-mande l a t e
Figure 1. Infrared spectra of amphetamine d-mandelate salts in KBr between 800 and 600 cm-I
tories. A gas-liquid chromatographic method has also been developed (2) using N-trifluoroacetyl-(I)-prolyl chloride to form diastereoisomeric derivatives with d- and l-amphetamine. This author has developed a simple method by which three distinct infrared spectra can be produced for d-, dl-, and I-amphetamine as the d-mandelate salts.
(1) Methods of Analysis of the A.O.A.C. 10th ed.: 1965, William Horwitz, Ed., p 597. (2) Clyde E. Wells, J. Ass. Ojjic. Anal. Chem., 53, 113-115 (1970).
RESULTS AND CONCLUSION
The resulting spectra of the different isomers show several differences, the greatest being in the 800-600 cm-l region as illustrated in Figure 1. The differences in the three spectra are certainly sufficient to distinguish d-, dl-, and I-amphetamine. This method has been used successfully on several samples of illicit amphetamine tablets. Only impurities precipitated by mandelic acid will interfere and none have been encountered in samples. Other optically active drugs can probably be distinguished using d-mandelic or other acids. RECEIVED for review April 30,1970.
Accepted July 15,1970.
ANALYTICAL CHEMISTRY, VOL. 42, NO. 12, OCTOBER 1970
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