methods for impurity profiling of heroin and cocaine - United Nations ...

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-1,3dicarboxylic
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 isomeric
truxillines in illicit, refined, South American cocaine hydrochloride using capillary
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 approximately
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 internal
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.