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

Methods for impurity profiling 33
Internal standard stock (ISS):* d 6 -acetone at 6 mg/ml, d 9 -2-chloro-2-methylpropane at
3.5 mg/ml, d 14 -n-hexane at 1.5 mg/ml, d 8 -isopropanol at 7.5 mg/ml and d 8 -toluene at
1.5 mg/ml in dimethylsulfoxide (DMSO).** All standards should be +99.5% pure.
22% sodium sulfate solution: 220 gm of +99% anhydrous sodium sulfate in one litre
of deionized water. Between use, store at room temperature.
Dilute internal standard solution (DISS): Add 100 µl of the ISS for each 100 ml of
22% Na 2 SO 4 solution. Prepare daily.
Standard stock solutions (SSS): Methanol, ethanol, acetone, isopropanol, n-butanol and
isobutanol at 0.4 mg/ml; methyl ethyl ketone, ethyl acetate, chloroform, methylene
chloride, 1,1,2-dichloroethane, ethyl ether, methyl acetate, cyclopentane, isobutyl
acetate, n-butylethyl acetate and 1,1,1-trichloroethane at 0.2 mg/ml; cyclohexane, benzene,
toluene, n-hexane, o-xylene, p-xylene, mesitylene and mesityl oxide at 0.08
mg/ml. Two additional calibrations solutions are created by making two 1:5 serial
dilutions.*** All dilutions are made using a solution of DMSO:water (5:1). Label the
solutions SSSH, SSSM, SSSL respectively from the highest to the lowest concentration
solution.
Calibration solutions: Add 5 ml of DISS to four 22-ml headspace vials, then add 50
µl of SSSH to the first vial, 50 µl of SSSM to the second vial and 50 µl of SSSL to
the third vial. The fourth vial is used as a run blank (standard zero point) as it contains
only the DISS. Immediately seal each vial tightly with a silicon/polytetrafluoroethylene
(PTFE)-lined cap.
Sample preparation: Accurately weigh approximately 50 mg equivalent of heroin base
into a 22-ml headspace vial, add 5 ml of DISS. Immediately seal each vial tightly
with a silicon/PTFE-lined cap.
Rationale for use: The method provides facile detection to the 0.00001% level and
reproducible quantification to the low 0.0001% level relative to the heroin content
and, with minor modification, is utilized for both heroin and cocaine samples. The
method requires a special injector device. Also requires the acquisition of appropriately
deuterated standard materials; however, a few millilitres of the standard materials
will last for a considerable period of time.
Outcome: Allows access to solvents trapped within the crystal matrices of samples
without decomposition of solvents or other sample components. The method provides
nearly comprehensive detection of all sample solvents and, very importantly, allows
the accurate assessment of the relative importance of the detected solvents.
*The internal standard stock is stable for up to two months if stored in the dark at -10° C
between uses.
**Deuterated standards were from the Cambridge Isotope Laboratories, 50 Frontage Rd.,
Andover, Massachusetts, United States.
***The calibration standards solutions were found to be stable up to four weeks if maintained
in the dark, at -10° C, between uses.