The determination of morphine in opium

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The determination of morphine in opium
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Author: Ustik AVICO
Pages: 1 to 3
Creation Date: 1967/01/01

The determination of morphine in opium *

Ustik AVICO
Istituto Superiore di Sanité, Rome

Summary

The purification of the aqueous extract of opium by filtration through (acid) aluminium oxide makes it possible to obtain greatly improved results in the precipitation of morphine base with lime methods.

The proposed modification consists essentially in a complete morphine extraction followed by filtration through (acid) aluminium oxide: many analyses of this extract can be made with different methods (Mannich and lime method).

By means of this purification, a more complete precipitation of morphine with lime methods is obtained; in unfavourable cases, where opium samples contain a number of substances hindering precipitation, better results are obtained than by traditional methods, without introducing arbitrary correction factors.

The determination of morphine in opium

Although a great many methods have been proposed for determining the morphine content in opium-including methods based on the formation of condensation products and the weighing of those products [ 3] , [ 6] , [ 7] , [ 12] , on oxido-reduction [ 1] , [ 5] , [ 10] , on colour reactions [ 8] , [ 9] or on chromatographic separation-the official methods are exclusively those using lime (sometimes ammonia or borax) and based on the precipitation and weighing (or volumetric analysis) of the morphine base.

These past-mentioned methods, however, can produce widely divergent results, which are moreover nearly always underestimates.

The modification here proposed of the USP XVI and the Pharmacopœia Internationalis (first edition, 1951) methods makes it possible to obtain a reproducible result without introducing arbitrary correction factors, and a greatly improved approximation.

Sampling

Approximately 5 to 6 g of opium are weighed on a technical balance in a weighing bottle, the weight of which has been previously ascertained on an analytical balance; the opium is then weighed to the nearest mg (P).

The original of this article is in Italian.

Extraction and purification

The opium is triturated finely in a mortar, and 10 g of (acid) aluminium oxide (for chromatography) and 50 ml of water [ 11] are added gradually. The homogeneous mixture in the mortar is stirred at frequent intervals for approximately 15 minutes and is then transferred to a sintered glass filter 4 cm in diameter and 8 to 10 cm high, containing a column of 40 g of (acid) aluminium oxide (for chromatography) which has been previously washed with water until the filtrate is clear [ 3] . (It is advisable not to wash the column excessively because it will become clogged, which hinders subsequent filtration.)

Filtration is facilitated by slight suction and washing is continued, the upper layer of aluminium oxide being suspended each time with 10 ml of water. This operation is repeated until the filtrate no longer contains morphine (negative Guarino polyreaction [ 4] ). This result is arrived at after 300 to 350 ml of filtrate have been collected.

The filtrate is then transferred to a rotating evaporator, concentrated to a weight of slightly less than 180 g, and brought up to 180 g exactly by successive addition of water (S).

Determination of morphine by the Mannich method

A quantity of the filter solution (S) (which, in the case of some varieties of opium, may still be opalescent) equivalent to 1 g of opium is transferred, if necessary after quickly filtering it through filter paper, to a previously weighed 100-150 ml flask with a ground-glass stopper:

m = 180/P, where P is the weight of the sample.

This quantity (m) is precipitated by the Mannich method [ 12] by means of para-chlorodinitrobenzene, following the procedure briefly described below:

Water is added until the weight of the aqueous solution is brought up to 36 g; a solution of 0.25 g para-

chlorodinitrobenzene in 30 ml of acetone is then added. The solution is shaken and 4 ml of concentrated ammonia solution is added (26 B?; 28%).

The solution is shaken for a few minutes and allowed to stand in a cool place, away from light, for one night.

The precipitate is then collected in a small filter which has been previously weighed. It is then briskly washed (for 10 to 15 minutes), twice in 2 ml of acetone and twice in 2 ml of water.

The filter is then dried at 70-100°.

The weight of the precipitate multiplied by 63.2 gives the anhydrous morphine base content per 100 g of undried opium.

Determination of morphine and codeine

A quantity (p) corresponding to 4 g of opium is then taken from the remaining filtrate (S):

P
=
180.00 x 4/4
=
720/P

This is concentrated in a rotating evaporator working under a vacuum to less than 41 g. It is then transferred, without losses as before, to a weighed 150-200 ml flask with a ground-in stopper. The weight is brought up to 41 g and 1 g of Ca(OH) 2 is added.

The liquid is then shaken for about ten minutes and is filtered through a dry sintered glass G3 filter approximately 3-4 cm in diameter and 5-6 cm high without washing. The filtration process is speeded up with the help of slight suction.

From 25 g of the clear filtrate thus obtained the morphine is precipitated by the International Pharmacopœia methods which are briefly described below:

  1. Determination of morphine by the lime method

A quantity of 25 g of liquid is placed in a 100-150 ml flask with a ground-glass stopper and 2.5 ml of 90 per cent ethyl alcohol and 12.5 ml of ethyl ether are added. The mixture is shaken and 1 g of ammonium chloride is added. The mixture is further shaken (for 30 minutes, according to the International Pharmacopœia; but since this solution is purer, precipitation nearly always begins after a few minutes) until the morphine begins to precipitate. It is then allowed to stand in a cool place, away from light, for one night.

It is then filtered through a sintered glass G4 filter, care being taken not to cause much evaporation of the ether phase (which contains the codeine) during the filtering process.

The two filtered liquid phases are then transferred to a 100 ml separating funnel. The flask, the stopper and the filter are washed twice with 10 and 5 ml of ethyl ether which are poured into the separating funnel. They are then washed again with 1.5 to 2 ml of cold saturated aqueous morphine solution which is poured into the separating funnel.

The process of washing the flask, the stopper and the precipitate on the filter with 3 ml each time of morphine-saturated solution is continued, regardless of the successive filtrates obtained, until the Cl-ions disappear from the filtrate.

The flask, stopper and filter with precipitate are rapidly dried in an oven. They are then washed four times with 10 ml of hot methyl alcohol; the solution is passed slowly through the filter each time, so that the whole quantity of the morphine is dissolved.

The methanol solution is then titrated with 0.1 N hydrochloric acid or sulphuric acid, using methyl red as an indicator. When the solution turns orange 120 ml of freshly boiled and cooled water are added. The titration is continued until the liquid turns a pinkish-red colour.

The morphine content in grammes per 100 g of opium is calculated using the formula:

M
=
2.8533 x 41.00/25.00 x 4.000
ml
=
1.17 ml
  1. The determination of codeine

The two phases in the separating funnel are shaken up and separated. The aqueous phase is extracted with an additional 5 ml of ethyl ether and the ether phases are washed with 5 ml of water.

The residue is isolated from the combined ether phases after drying them with anhydrous sodium sulphate and evaporating the solution to dryness.

The codeine is determined by polarimetry or by the Bose method [ 2] from the resulting solution by dissolving the residue with an appropriate quantity of dilute hydrochloric acid.

Results and discussion

Of twenty samples tested, the table below shows the seven which, with the use of the traditional methods (see columns 3-4 and 6), gave the most divergent results.

A comparison with the results obtained using the change in method now proposed (see column 8) shows a striking improvement in the estimation obtained.

Results of analysis of the opium samples tested

 

International Pharm.

 

Proposed modification

No.
Origin
Mannich method
Corrected
Without correction
USP XVI
Mannich method
Lime methods
00
India ...
11.60 9.49 8.28
__
11.65 9.42
08
India ...
12.40
10. 11
8.91
_
11.13 10.25
13
doubtful.
11.40 3.73 2.52 7.56 11.40 9.18
14
Turkey...
13.83 7.38 6.17 11.25 14.10 12.11
17
India...
11.58 9.27 8.06
-
12.27 10.41
18
India...
11.35 8.14 6.84 7.86 11.58 9.71
19
doubtful.
12.48 8.92 7.71 8.62 11.89 9.77

The proposed modification thus has the following advantages:

  1. quicker sampling, since weighing within strict

limits is not required;

  1. complete extraction of the morphine;

  2. more complete precipitation of the morphine with the lime method; without fixed correction coefficients (about 1.2 per cent with the International Pharmacopœia method and about 1.6 per cent with F.U. VII), the figures obtained are distinctly higher than with the other lime methods including USP XVI);

  3. consequently, in the most unfavourable cases, the actual morphine content can be determined within narrower: limits: the approximation on the low side provided by the proposed lime method and the approximation on the high side provided by the Mannich method;

  4. simultaneous approximate determination of any codeine present as such in the opium

Biological Laboratories

Istituto Superiore di Sanité

Bibliography

001

Bentley, K. W.; The chemistry of morphine alkaloids, 1954

002

Bose, P. C.; Jour. Sci. Ind. Res. 21 D, 386 (1962)

003

Fischer, R.; Folberth, K.; Arzneim. Forsch. 5, 66 (1955)

004

Guarino, S.; Arch. Sci. Biol. 31, 115 (1946)

005

Kieffer, L.; Ann. 103, 271 (1857)

006

Mannich, C.; Arch. Pharm. 273, 97 (1935)

007

Mannich, C.; Arch. Pharm. 280, 386 (1942)

008

Mariani, A., Guarino, S., Mariani, Marelli, O.; Annali Chim.41, 661 (1951).

009

Mariani, A., Vicari, C.; Rend. Ist. Super. San. 19, 240 (1956)

010

Pruner, G.; Rend. Ist. Super. San. 19, 492 (1956)

011

Pruner, G.; U.N. Document ST/SOA/SER.K/101 (1960)

012

Toffoli, F.; Rend. Ist. Super. San. 20, 155 (1957)