Tewari S.N., and J.D. Sharma. "Spot tests for cannabis materials" Bulletin on Narcotics, Vol 34 No 3 1982 pp 109-112
S. N. TEWARI and J. D. SHARMA
Forensic Science Uboratory, Utlar Pradesh, Lucknow, India
Sensitive and specific spot tests are described for the identification
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
 describe a method for marijuana screening based on the spot test, whereas
de Faubert Maunder  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  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
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,
1979, pp. 196 - 197.
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