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Clinical Chemistry 17: 1016-1019, 1971;
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Clinical Chemistry, Vol 17, 1016-1019, Copyright © 1971 by the American Association for Clinical Chemistry

Improved Colorimetric Method for Assay of Amphetamines in Urine

Christopher S. Frings 1, Cecelia Queen 1, and Lowell B. Foster 1

1 Medical Laboratory Associates, 1025 S. 18th St., Birmingham, Ala. 35205.

The increasing abuse of drugs makes it imperative to have rapid, selective methods for their detection. Methods for amphetamines in which methyl orange is used as a reagent are subject to interference by a number of drugs. In the present modified, improved method, amphetamines combine with methyl orange to form a chromogen that follows Beer’s law at 515 nm to amphetamine concentrations of 10 mg/100 ml. Most interfering drugs are removed by pre-extraction into chloroform at pH 5.5. Of over 40 commonly used drugs, including organic bases and alkaloids, only amphetamine, dextroamphetamine, methamphetamine, and pentazocine HCl ("Talwin") react to produce a chromogen in this method. Recovery of amphetamine added to serum and urine is essentially 100%, as compared with aqueous standards taken through the entire procedure. The coefficient of variation is 8.9%. The method described, far more (but not completely) selective for amphetamines than previous methyl orange methods, is rapid, precise, and sensitive, which makes the method valuable in drug abuse screening programs—for which the speed is even greater, because only information on the qualitative presence or absence of amphetamines is required.


Key Words: methyl orange—drug complex • specificity • drug-abuse screening • extraction

Submitted on June 7, 1971
Accepted on June 30, 1971






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Copyright © 1971 by the American Association for Clinical Chemistry.