Abstract
Introduction
Laboratory method Apparatus
General analytical scheme for opium
Field test method
Absolute confirmation of opium
Results and discussion
Conclusions
Author: M.J. de FAUBERT MAUNDER
Pages: 71 to 76
Creation Date: 1975/01/01
Two new colour tests for opium are described. These may be used alone, as field tests, or in combination with traditional tests rapidly to confirm raw or prepared opium. Absolute confirmation of opium by thin layer chromatography is also useful in the determination of origins. An alternative chromogen to the Dragendorff reagents is described, although iodoplatinate remains the preferred chromogen.
Current United Kingdom legislation [ 1] makes a distinction between "raw opium" and "prepared opium". The analyst is, therefore, required to confirm which form is involved because of the absolute prohibition on prepared opium and its correspondingly more stringent penalties.
A survey of Her Majesty's Customs and Excise seizures over a period of years has revealed that the differences between raw and prepared opium are overlooked in some laboratories, and that erroneous identification of old raw opium as "prepared opium" is the rule rather than the exception. It is assumed that the brittle nature of old raw opium and its lack of a marked odour, coupled with the infrequency of encounter, lead to this situation, particularly if confirmation is confined to mere identification of morphine content. In these circumstances, the lay-experience of Customs officers is frequently more accurate than the analyst.
Many authentic samples, based partly on an international collection assembled over a number of years, are available for study, and methods for correctly identifying opium in its varied forms have been developed by the Laboratory of the Government Chemist from this collection. The methods are based, for the most part, on simple colour tests together with appearance and odour so that a laboratory can carry out a correct analysis without recourse to instrumental methods and reference samples. Where reference samples are available, thin layer chromatographic analysis can be carried out to study minor components in some detail and tentatively correlate sources of supply.
The methods presented here allow a rapid confirmation of the presence of opium. The thin layer technique is presented for completeness and will probably be found to be of more use in confirming that two opium samples are dissimilar, rather than that they are identical.
Whatman filter paper No. 1 (5.5 or 7 cm. diameter), or equivalent grade.
Spot tiles
Test tubes
Thin layer chromatographic apparatus, preferably small-scale or "S" tanks
* The author wishes to thank the Government Chemist for permission to publish this paper.
Commercial grade reagents are suitable:
Mayers - Potassium mercuri-iodide solutions; of the British Pharmacopoeia
Wagners - Iodine solution; of the British Pharmacopoeia
Marquis - I ml. commercial formalin solution (approximately 40% formaldehyde solution in water) in 100 ml. concentrated sulphuric acid (sg: 1.84)
Mecke - 1 g. selenious acid in 100 ml. concentrated sulphuric acid (sg: 1.84)
Froehde - 0.5 g. molybdic acid or sodium molybdate in 100 ml. concentrated sulphuric acid (sg: 1.84)
It may be necessary to warm to effect solution; the reagent should be colourless but usually develops a pale pink colour
Mandelin - 1 g. ammonium metavanadate in 100 ml. concentrated sulphuric acid (sg: 1.84)
2 N hydrochloric acid
5. g ferric sulphate in 100 ml. water
5 g. 4-dimethylaminobenzaldehyde in 100 ml. concentrated phosphoric acid (sg: 1.75): methanol: 1:1
Chloroform
Methanol
Iodoplatinate or alternative alkaloid chromogen
Cobalt thiocyanate chromogen: 5 g. cobalt thiocyanate in 50 ml. methanol diluted to 100 ml. with 2 N hydrochloric acid
5 g. mercuric chloride in 100 ml. water
The appearance and odour of both raw and prepared opium are usually diagnostic. Opium dross also has its own characteristic appearance (often "granular") and odour; for analysis, treat as "prepared opium".
Dissolve a small quantity in cold water (ratio 0.1 g. to 1 ml.) and filter: Note the characteristic appearance and odour.
Place a maximum of one drop of this solution 2. in each of four depressions in a spot tile and add 4-5 drops of one of the following reagents to each noting the speed and hues of transient colours. The following colours are diagnostic:
|
Reagent |
Colour after 1 min. |
|---|---|
|
Marquis
|
Pink to purple
|
|
Mecke
|
Green to blue green
|
|
Froehde
|
Strong violet
|
|
Mandelin
|
Muddy brown
|
Add 1 drop of 2 N hydrochloric acid to the remaining filtrate from 2. and add up to 5 drops of ferric sulphate solution. If there is a red colouration, split into two portions -
To portion ( a) add the same volume of 2 N hydrochloric acid and warm;
To portion ( b) add a few drops of mercuric chloride solution.
Opium gives a persistent red colour in both portions.
Dissolve a further small quantity of sample in warm 2 N hydrochloric acid (ratio 0.1 g. to 1 ml.) on a steam bath and filter; raw opium gives a characteristic red appearance and acrid odour.
Use this acid digest for the next two tests and for thin layer chromatography.
Mayers reagent. If opium is present, the acid digest gives an immediate gelatinous white precipitate.
Wagners reagent. Opium gives an immediate blackish precipitate.
Place about 1 mg. of suspect material on a filter paper and add one drop of improved hallucinogen reagent (2) (Reagent 9). A pink colour develops in the paper as the fluid spot dries, usually within 5 minutes.
Heat to boiling about 1 mg. of suspect material with a few drops of 2 N hydrochloric acid in a test tube. As with the Meta Duquenois test (3), a match or cigarette lighter provides adequate heat for a field kit. A red colouration, with some insoluble matter indicates raw opium; a clear brown solution indicates prepared opium. Both materials yield characteristic odours.
Further confirmation may be obtained from the solution derived in the previous test using any other published test, such as the Marquis test.
In routine practice, in experienced hands, the General Analytical Scheme tests constitute adequate confirmation of both raw and prepared opium. There may be circumstances where all of the tests are not a practical proposition, for example, in pipe residues, or where evidence of a common composition is required.
In these circumstances, examine a comparable amount of the sample and the reference standard by thin layer chromatography using comparable quantities of reagents and standardised conditions; the following system has been found suitable:
4 x 4 cm. "Chromagram" sheet 6060 (silica gel with fluorescent indicator), or its equivalent.
25 to 0.5 ?l. aliquots of the hydrochloric acid digest from stage 5 of the General Analytical Scheme.
Chloroform/methanol: 9/1 as the mobile phase.
Micro or "S" tanks in which equilibration is not essential.
Visualisation by iodoplatinate spray and by 360 and 254 nm. ultraviolet illumination.
The improved hallucinogen reagent [ 2] responds rapidly to all opium samples examined. Fresh raw and prepared opium yield a pink colouration within 2 minutes, whereas, except for opium dross, all other samples yield the colour within 5 minutes. With raw opium, the pink colour deepens to a purple within a further 5 minutes.
The mechanism of this reaction is obscure. The colour reactions of the hallucinogen reagent to pure opiates indicates that this is not the predominant mechanism. These colours are summarized in table I.
The Wasicky reagent also uses 4-dimethylaminobenzaldehyde in a strong acid. This responds to the opiates within 5 minutes [ 4] . Opium, in common with many natural products, contains tryptophan and related compounds and these give pink to purple colours with 4-dimethylaminobenzeldehyde in acid solution (Ehrlich reagents). Romieu, in 1935 [ 5] observed a red colour with tryptophan-rich tissue treated with concentrated phosphoric acid. Boctor [ 6] applied this reaction and found it to have comparable sensitivity to an Ehrlich reagent for tryptophan. This suggests that both reactions are operative.
The hallucinogen reagent is available in test kit form [ 7] and a test scheme there includes detection of opium, preceded by a routine screening for cannabis. This hallucinogen reagent is found to be more effective than the Marquis reagent as a first-action test since the opium does not need to be first brought into solution, as provisionally recommended in a UN draft scheme of field tests [ 8] .
TABLE I
Colour developed by the common opiates with the hallucinogen reagent (2)
|
Colour developed |
Minutes taken |
|
|---|---|---|
|
OPIATE
|
||
|
Morphine hydrochloride
|
faint pink
|
25 |
|
Codeine phosphate
|
pink
|
15 |
|
Thebaine hydrochloride
|
yellow
|
4 |
|
Papaverine hydrochloride
|
nil-
|
-
|
|
Papaverctum BPC
|
faint pink
|
20 |
|
Ethylmorphine hydrochloride
|
pink
|
25 |
|
Diamorphine hydrochloride
|
faint pink
|
40 |
|
Pethidine hydrochloride
|
nil
|
-
|
|
OPIUM
|
||
|
Prepared and fresh raw
|
pink
|
2 |
|
Old raw
|
pink
|
about 5
|
Confirmation of the tryptophan test is normally carried out by heating with dilute hydrochloric acid. The red colour and characteristic odour developed in boiling hydrochloric acid is found to be the simplest single test for raw opium. Further confirmation may be achieved with this solution using the Marquis test or the meconic acid test of Butler [ 9] , as further modified [ 8] . The comparison of raw and prepared opium is given in table II.
TABLE II
Distinguishing features of raw and prepared opium
|
Raw opium |
Prepared opium |
|---|---|
|
1. Appearance. Fresh opium is usually very sticky and may often have an outer covering of poppy leaves Stale opium is a brittle solid.
|
Prepared opium may be a treacly-like mass but is more often encountered in quantities of about 1 g. as a brittle solid wrapped in grease-proof paper.
|
|
2. Odour. If no obvious odour issues from the bulk material, crush a minute amount in the fingers..
Odour of poppies
|
Little or no odour ; odour of treacle most common.
|
|
3. Treatment with water.
|
Relatively little insoluble matter.
|
|
Copious insoluble matter.
Slow filtration Opium odour.
|
Filters readily.
No odour or a treacle odour; a meat extract type odour has sometimes been noted.
|
|
4. Test 3 of main scheme.
Colour tests are normally weak and slow to develop; they are best recognised by experience and by carrying out comparison tests at the same time.
|
Bright, strong colours
|
|
5. Treatment with hot 2
N hydrochloric acid.
Pink solution with some insoluble matter
Characteristic acrid odour.
|
Brown solution with little insoluble matter..
Less unpleasant odour, often "meaty"
|
It is generally stated that all reagents should be freshly prepared, but in practice, this is not found to be essential, although the speed and clarity of colour development for fresh reagents based on sulphuric acid is markedly better. The normal speed and colour development should be established for the reactions in Table II with the reagents in their original and stored condition, and due allowance made for the reagents immediately to hand if these differ. All reagents keep for at least one year at normal temperatures, but the Mandelin reagent tends to deposit a yellow precipitate; the supernatant liquid remains useful for some time.
In the thin layer chromatographic confirmation of opium, morphine is poorly extracted by most simple aqueous processes. The absence of a large morphine spot must, therefore, be expected. The use of the acid digest avoids additional preparation stages and yields a total alkaloid extract.
Reference spots of the major alkaloids may be run for comparison. A logical standard is Papaveretum BPC, dissolved in water. Amongst other differences, the alkaloids may run as salt complexes, leading to "ghost images". The use of basic plates, or a base component in the mobile solvent is recommended to avoid this.
The pattern of spots obtained on the thin layer chromatogram is a diagnostic feature for common origin confirmation. The minor components, most of which will be unidentified, are matched for Rf, colour and intensity and provide an effective "fingerprint". The morphine spot size varies according to the care taken in comparative extractions, and must not be used in the comparisons. Extra confirmation of common origin is provided by two dimensional tlc. In the example cited using chloroform/ methanol as mobile solvent, a solvent system containing a base is recommended as the second system as this will yield extra information if the alkaloids run as salt complexes in the first system.
As for the determination of the common origin of cannabis samples [ 10] , a suitable second solvent has been found to be 2% v/v diethylamine in toluene. A considerably higher proportion of diethylamine must be used if an absorbent other than "Chromagram 6060" (Proprietary silica gel on polyester sheets) is employed. Alternatively, more complex solvent mixtures may be required. The opiate resolving power of some of these is reviewed by Butler [ 9] . Stahl [ 11] has applied thin layer chromatography in a similar manner for the characterization of opium and its preparations. Both these authors use Dragendorff reagents as a chromogen. Iodoplatinate chromogens generally give better colour discrimination, but, for "Chromagram" sheets, both these reagents normally require dilution for optimum results. Where Dragendorff reagents must be used for economic reasons, an adequate colour discrimination and comparable sensitivity have been found with the improved cocaine test reagents [ 12] .
The optimum concentration is determined by the brand of absorbent and is not critical. Acceptable results may be obtained with reagent B [ 12] that is a concentration of cobalt thiocyanate ranging from 1 to 5% w/v in 2 N hydrochloric acid. Faster responses and improved spraying characteristics, are obtained with reagent A, in which the aqueous acid is replaced by a 1:1 mixture of 2 N hydrochloric acid and methanol. Again, the cobalt thiocyanate concentration is not critical and may range from 1 to 5 w/v depending on the absorbent. A concentration of 2.5 % specified in the list of reagents will operate efficiently for all absorbents, and need not be weighed accurately due to the wide reagent tolerance. In all cases, the plates should not be over-wetted or spot diffusion occurs.
A new colour test is presented as a suitable field test for opium, using a reagent already available in a test kit. A second colour test is suitable as a confirmatory test, and provides the simplest single test for raw opium. These, and other confirmatory tests, may be carried out with milligrame-sized samples. The residue from the second test is convenient in a laboratory for direct thin layer chromatographic confirmation of the field test.
Misuse of Drugs Act 1971, HM Stationery Office, London.
002M.J. de Faubert Maunder, J. Pharm. Pharmacol., 26 , 637, 1974.
003M.J. de Faubert Maunder, Bull. Narcot., 21 (4), 37, 1969.
004C.G. Farmilo, et al., Bull. Narcot., 4 (4), 16, 1952.
005M. Romieu, Comptes rendus Acad. Sci. Paris, 180 , 875, 1935.
006F. N, Boctor, J. Chromog., 67 , 371, 1972.
007Drug Test Kit, BDH Chemicals Ltd., Catalogue Number 32148.
008United Nations Report MNAR/2/74.
009W. P. Butler, United States Internal Revenue Service, Publication No. 341 (Rev. 6-67).
010M.J. de Faubert Maunder, J. Assoc. Public Analysts., 8 , 42, 1970.
011E. Stahl, Arzneim. Forsch ., 1969, 19, 194, 1969.
012G.V. Alliston, et al., ,4nalyst ., 97, 263, 1972.
