Total analysis of an illicit or "street" narcotic sample by thin-layer chromatography
Author: Leopold MAY , Chi-li T. KUO
Pages: 35 to 36
Creation Date: 1972/01/01
Chi-li T. KUO Research Assistant, Department of Chemistry, Catholic University of America, Washington, D. C., 20017 (U.S.A.)
A procedure has been developed for the total analysis of an illicit narcotic sample using thin-layer chromatography. The sample is dissolved in water. Any residue is removed by centrifugation for further analysis. The clear solution is extracted with methanol-chloroform-ammonia solution. The organic and the aqueous phases are subjected independently to thin-layer chromatography. The results of the chromatography of the organic phase give the alkaloid constituents, and the results from the aqueous phase give the sugar constituents.
As the first step in a program to inform potential users and medical personnel of the occurrence of deleterious non-narcotic substances in illicit or "street" narcotic samples available to the public, a procedure for the total analysis of the sample was needed. The desired procedure was to determine all the constituents in the sample, be rapid, and require small amounts of the sample. The usual illicit sample contains the active narcotic drug and one or more diluents. These diluents may include alkaloids, sugars, and insoluble substances such as starch. Thin-layer chromatography (TLC) is a method that satisfies all these requirements. In addition, the previous work on the TLC of alkaloids, sugars, etc., was useful in evaluating the best procedures to be used.
The diluents in the illicit sample may be a single substance or a combination of several. The substances used as diluents have been sugars, for example, maltose, alkaloids (quinine) used in combination with the sugar, and water insoluble materials, such as starch. The basic procedure (see diagram) is based upon the solubility of all constituents in water and the subsequent extraction of the alkaloid or alkaloids with methanol-chloroform
(3:1) treated with ammonia [ 1] . Any insoluble material after extraction of the sample with water is removed by centrifugation and analyzed separately. TLC of both the aqueous and organic solutions are performed. The results of the application of the procedure to synthetic mixtures are described in this report.
For the total analysis of a sample, one mg of the sample is dissolved in a minimum of distilled water (usually about 1 ml) in a 15 ml centrifuge tube. If there is a precipitate, the suspension is centrifuged. The supernatant or the original solution is extracted with the methanol-chloroform (3:1) to which a small amount (1 or 2 drops) of aqueous ammonia has been added. After shaking, the two layers are separated using a medicine dropper. The lower or aqueous phase contains the water soluble materials such as sugars. The upper or organic phase contains the alkaloids.
Ten µl of the aqueous phase are spotted on a TLC plate and developed with butanol-acetone-water (40: 50:10) for one to one and one-half hours [ 2] . After drying the plate is sprayed with naphthoresorcinol (0.2 % alcoholic solution mixed with equal volume of 20 % sulfuric acid). The TLC plate is then dried for five to ten min at 100-105 °C. The sugars, if present, appear as purple spots.
The organic phase containing the alkaloids is spotted on the same type of TLC plate, but developed with chloroform-ethanol (9:1) solution for one to one and one-half hours [ 3] . The plates are air-dried, and the spots visualized with iodine vapor.
In these experiments, TLC plates coated with silica gel G, thickness of 250 microns were used. For example, Uniplate (Analtech, Inc., Wilmington, Delaware) were used without any further treatment.
The procedure involves the extraction of the aqueous solution of the illicit sample with methanol-chloroform-ammonia. After mixing, some of the organic solvents may dissolve in the aqueous phase. This would change the concentrations of the solvents in this phase and may change the behavior of the sugars on the TLC plate. To test this, the R F values were measured for the sugars dissolved in water and for an aqueous solution of the sugars that had been treated with the organic solvent. As can be seen from the table, the values of the R F are slightly higher after treatment of the solution with the ammoniacal organic medium.
Effect of extraction with methanol-chloroform-ammonia on R F of sugars in aqueous phase
aAqueous solution after extraction with organic solution.
To test the effectiveness of the extraction of the alkaloid into the organic phase, the aqueous layer of an alkaloid solution after extraction was spotted on a plate, and the chromatogram developed with the solvent system used for the alkaloid separation. No spots appeared on the TLC plate. Similarly, a water solution of maltose was extracted with the non-aqueous solvent. The organic extract was spotted on a TLC plate and developed with the solvent system used to separate the sugars. No spots appeared on this TLC plate indicating that under these conditions, none of the sugars are soluble in the non-aqueous phase. Thus, this procedure separates the two classes of substances (alkaloids and sugars) in the concentration range used (1 mg/ml).
To test the system using actual samples, a mixture of heroin hydrochloride (0.5 mg), quinine sulfate (0.5 mg), and maltose (1 mg) was prepared. After extraction, the TLC of the organic phase showed two spots at R F of 0.26 (heroin) and 0.39 (quinine). The TLC of the aqueous phase gave one spot at R F of 0.62, which is characteristic of maltose. The procedure was tried with a Methadon hydrochloride tablet (Abbot Laboratories). The residue after extraction with water was identified as starch with iodine. The TLC of the organic phase gave one spot at a R F of 0.17. One spot was also found upon chromatographing the aqueous phase at a R F of 0.57, which is characteristic of lactose in our solvent system.
The authors thank Dr. David Nurco of the State Department of Health and Mental Hygiene for suggesting the problem and his advice. We gratefully acknowledge the assistance and advice of the members of the U.S. Customs Laboratory, Baltimore, Maryland, particularly Messrs. Alvin Bober and Albert Mills, and that of Mr. Willard Washington of the Alcohol, Tobacco and Firearms Division of the U.S. Treasury Department, Washington, D.C.
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