Spot tests for cannabis materials


Results and discussion


Author: S. N. TEWARI, J. D. SHARMA
Pages: 109 to 112
Creation Date: 1982/01/01

Spot tests for cannabis materials

Forensic Science Laboratory, Uttar Pradesh, Lucknow, India


Sensitive and specific spot tests are described for the identification of cannabis materials. These spot tests are economical since they utilize minimal amounts of cannabis derivatives and chromogenic reagents. They yield satisfactory results when applied to the cannabis materials and are sensitive at less than 10 μg/ml. The described spot reactions are simple, highly reliable and reproducible.


Spot tests are very useful where the quantity of any drug to be detected is small. They have an edge over customary colour reactions which often fail not because the concentrations are different, but because the absolute quantity of the reaction product contained in one drop is not sufficient for it to be positively identified. A general account of such tests has been reported by FeigI [ 1] , [ 2] , but a perusal of the literature reveals that only a few researchers have employed spot tests for the identification of cannabis materials. Fiorese and others [ 3] describe a method for marijuana screening based on the spot test, whereas de Faubert Maunder [ 4] suggests the use of Fast Corinth V and 1-diazo-4-benzoylamine-2,5-diethoxybenzene with so-dium bicarbonate as chromogens for spot tests on filter paper. Recently Tewari and Sharma [ 5] reported on a series of specific and sensitive colour reactions for cannabis products. In view of the heavy abuse of these substances throughout the world, attempts have been made to develop a series of reliable and sensitive spot tests that may be effectively used for cannabis identification.



Amounts of 100 mg of cannabis resin, 1 g of the flowering tops (ganja) and 1 g of the cannabis leaves (bhang) were separately digested in 10 ml of chloroform with two drops of glacial acetic acid for 2 hours at room temperature. Each extract was filtered through Whatman paper No. 1 and evaporated at 35°C to dryness. Each residue was taken in 25 ml acetone and digested again with activated charcoal for about 1 hour to achieve decolourization. The extracts were filtered through Whatman paper No. 1, gently evaporated to dryness and each residue was placed in ethanol for spot reactions.

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For the conduction of spot tests, micro-quantities of cannabis solutions were spotted either on a thin-layer chromatographic plate of silica gel G or on strips of Whatman paper No. 1. After the spot dried, the sample was treated with chromogenic reagents (see table 1). One drop of one of the chromogenic reagents A was applied to the sample spot followed by one drop of chromogenic reagent B, C or D as shown in table 2. The colours either appeared instantaneously or developed gradually. The colour com- binations and sensitivity levels are indicated in table 2.

Results and discussion

Eight spot tests were introduced for the identification of different cannabis drugs. These spot reactions yielded satisfactory results with all cannabis materials tested in this study on both reaction surfaces, i.e. gel layer and filter paper strips. However, better results were obtained with the former. The spot test with cinnamaldehyde was the most sensitive, of the order of 0.1, 0.5 and 2.0 µg/ml respectively for cannabis resin, ganja and bhang. It instantaneously produced a red-orange colour, which was observed to vanish gradually. Other highly sensitive reactions were observed with dodecamolybdophosphoric acid and Fast blue salt RR which rendered fairly satisfactory results in the range of 0.1 - 4 µg/ml. Sensitivity was measured by repeated observations using different dilutions of the product.

The spot tests described were found to be a screening method superior to customary test tube colour reactions used for cannabis. The utilization of minimal amounts of drugs and chromogenic reagents distinctly effected meant the tests were economical in both materials and time. Moreover, the adsorption and localized fixation of the reaction product on the reactionsurface invariably facilitated the identification of and concentration limit for cannabis products as compared with classical colour reactions. This fact is highlighted in table 2. The tests described were all simple, reliable and reproducible.


The authors wish to thank the United Nations Narcotics Laboratory of the Division of Narcotic Drugs, Vienna, Austria, which supplied them with the authenticated samples referred to in the text. Thanks are also due to the Bureau of Police Research and Development for the award of a fellowship and financial assistance to J. D. Sharma.



F. Feigl, Qualitative Analysis by Spot Tests - Inorganic and Organic Application (Amsterdam, Modern Publishing Company, 1937).


F. Feigl, Laboratory Manual of Spot Tests (New York, Academic Press, 1943).


F. F. Fiorese and others, "Drug detection on the spot", Health Laboratory Science , vol. 9, No. 4 (1972), pp. 240 - 264.


M. J. de Faubert Maunder, "An improved procedure for the field testing of cannabis", Bulletin on Narcotics , vol. 26, No. 4 (1974), pp. 19 - 26.


S. N. Tewari and J. D. Sharma, "Specific colour reactions for the detection and identification of micro-quantities of cannabis preparations", Pharmazie, vol. 34, 1979, pp. 196 - 197.