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Tewari S.N., and J.D. Sharma. "Spot tests for cannabis materials" Bulletin on Narcotics, Vol 34 No 3 1982 pp 109-112

Spot tests for cannabis materials

Forensic Science Uboratory, Utlar 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 ug/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 Feigl [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 sodium 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 2hours at room temperature. Each extract was filtered through Whatman paper No. 1 and evaporated at 35C 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.


    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 combinations 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 ug/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 ug/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 reaction surface 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. Shanna.


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

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

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

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

Tewari S.N., 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.

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