Methods for impurity profiling of heroin and cocaine

Methods for impurity profiling

41

Method D2:

GC method, with derivatization, electron capture detection (ECD)

Sources: J. M. Moore and others, “Capillary gas chromatographic-electron capture

detection of coca-leaf-related impurities in illicit cocaine: 2,4-diphenylcyclobutane-1,3-

dicarboxylic acids, 1,4-diphenylcyclobutane-2,3-dicarboxylic acids and their alkaloidal

precursors, the truxillines”, Journal of Chromatography A, vol. 410, 1987, pp. 297-318;

J. M. Moore, J. F. Casale and D. A. Cooper, “Comparative determination of total iso-

meric truxillines in illicit, refined, South American cocaine hydrochloride using cap-

illary gas chromatography-electron capture detection”, Journal of Chromatography A,

vol. 756, Nos. 1-2 (1996), pp. 193-201.

Operating conditions: 

Detector:

ECD – 

63

Ni (Agilent 6890 GC)

Make-up gas:

argon:methane (95:5) at 35 ml/min

Column:

DB-1701* or equivalent, 30 m x 0.25 mm x 0.25 µm

Carrier gas:

Hydrogen at 40-45 cm/sec as measured at 90° C

Injection size:

1 µl, splitless, Merlin microseal septa

Temperatures:

Injector: 275° C

Detector: 300° C

Oven: 90° C for 1.6 min, 25° C/min to 160° C for 1 min,

4° C /min to 275° C, hold for 5 min 

Internal standard: µ-truxinic acid and aldrin at 200 pg/µl in isooctane

Sample preparation: To an amount of unadulterated sample equivalent to 50 mg of

cocaine base is added 100 µg of µ-truxinic acid (internal standard) followed by 0.5 ml

of boron trifluoride (BF

3

-MeOH from Pierce, Rockford, Illinois, United States); the

solution is heated for two hours at 95° C. Cool solution to -10° C and with mixing add

2 ml of ice water and 6 ml of 20% NaOH (also at 10° C). Immediately extract five

times each with 5 ml of ethyl ether. Pass the extracts through anhydrous Na

2

SO

4

into

a 25-ml volumetric flask, dilute to volume with dry ether.** Evaporate 2 ml of the

ether solution to dryness under dry N

2

and then add 200 µl CHCl

3

and heat at 75° C

for 3 min. Add 4 ml of anhydrous ether and 200 µl of 1M LiAlH

4

(ethereal solution

from Aldrich, Milwaukee, Wisconsin, United States). Reduce the volume to approxi-

mately 500 µl at 50° C then carefully add 5 ml of H

2

SO

4

, mix and extract three times

with 5 ml of ethyl ether, passing each extract through anhydrous Na

2

SO

4

, and then

reduce just to dryness under a stream of dry N

2

. Add 1 ml of CH

3

CN and 50 µl of

heptafluorobutyric anhydride (HFBA) and heat at 75° C for 10 minutes. Add 10 µl

of “clean” pyridine and heat for two more minutes. Cool and add 8 ml of aldrin inter-

nal standard solution and 5 ml of saturated solution of NaHCO

3

, mix and separate

phases by centrifugation. Separate isooctane and dry it over anhydrous Na

2

SO

4

.***

Reference chromatograms: see annex III, figures VI and VII.

*The use of a moderately polar column is required in order to effect the separation of all

11 truxilline isomers.

**Ethyl ether maintained over 5 Å molecular sieve.

***Moore and Casale note in their article [54] that they are currently using an unpublished

modification of this method that significantly reduces analysis time.

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Method D3:

GC method, without derivatization**

Source: James Wong, Bureau of Drug Analysis Services, Health Canada, Burnaby,

British Columbia, Canada.

Operating conditions: 

Detector:

FID 

Column:

DB-5 or equivalent, 25 m x 0.32 mm x 0.52 µm

Carrier gas:

Helium 

Injection size:

1µl, split 25:1

Temperatures:

Injector: 250° C

Detector: 310° C

Oven: 160° C, hold for 3 min, 3° C/min to 255° C, hold

for 1 min, 20° C/min to 295° C, hold for 10 min

Internal standard: None 

Sample preparation: Dissolve 200-250 mg of cocaine sample in 5 ml of 0.5N sul-

phuric acid, add 5 ml of glass-distilled CHCl

3

and thoroughly mix the two phases.

Centrifuge to separate phases and discard the aqueous phase. Add to the CHCl

3

solu-

tion 5 ml of 0.5N sulphuric acid, mix thoroughly, centrifuge and discard the aqueous

layer. Transfer the CHCl

3

layer to a clean tube and evaporate to dryness at 45° C

under a stream of dry air of nitrogen. Reconstitute the dried residue in 50 µl of ace-

tonitrile:toluene (1:9).

42

Methods for impurity profiling of heroin and cocaine

Rationale for use: Relatively complex method that employs a reduction step with li-

thium aluminium hydride. The use of the isomeric µ-truxinic acid* as an internal stan-

dard greatly enhances method reproducibility and precision. The aldrin internal

standard functions only as a GC check standard. The method provides a summed quan-

tity for each of the 10 isomeric diphenylcyclobutyldicarboxylic acids found in E. coca

products by reducing the truxillines, and their hydrolyzed counterparts, to their cor-

responding diols. Derivatization of the diols with HFBA and the use of a moderately

polar column allows for the separation of all 11 possible isomers and when coupled

with electron capture detection (ECD) provides more than ample sensitivity. 

Outcome: Indicates the country of origin and allows sample comparisons for discrim-

ination and evaluation of samples for case-to-case evidential purposes (linkage deter-

minations). Provides additional information required to confirm links between samples,

that is, the method should be used in conjunction with a major component analysis.

*The µ-truxinic isomer is frequently not detected or, when detected, is at ultra-trace levels in

coca extracts; hence, it is a near perfect internal standard for the other 10 isomeric structures.

**The Health Canada Laboratory uses this method, with identical parameters and sample prepa-

ration, also for heroin (method B2). However, as pointed out, wherever possible, and especially

for comparative forensic purposes, the use of dedicated instrumentation and optimized method-

ologies is always preferred.

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