Methods for impurity profiling of heroin and cocaine



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Methods for impurity profiling

15

and, infrequently, even a significant amount of codeine. However, the analyst

should be careful when making this assessment as a dark brown (black) tar sam-

ple containing high O6MAM can arise from causes other than post-processing

hydrolysis. For instance, if a dark brown, tar-like sample contains high levels of

O6MAM along with significant quantities of O3MAM and little or no codeine, then

the sample could well have originated from a “homebake” process. Also the tar-

like dark brown heroin samples that originate in Mexico typically have a process-

ing-related O6MAM content higher than 6%, with 12% or greater (relative to

heroin) not being at all uncommon. It is thus not always a simple matter to dis-

tinguish between heroin samples that have undergone significant post-processing

hydrolysis and those samples where there was significant hydrolysis during pro-

cessing. Not surprisingly, the task of comparing two samples where one has under-

gone significant post-process hydrolysis versus one that has not undergone any

significant hydrolysis, although not impossible, is very much more difficult. There

are several publications included in the list of references [29-33] that will enhance

the reader’s understanding of the conditions necessary to produce O3MAM and

O6MAM.


Over time a properly prepared and stored heroin hydrochloride (or for that

matter cocaine hydrochloride) will not degrade in any significant manner. In this

context “properly prepared and stored” means fully hydrated +99.5% pure

hydrochloride salt containing no unbound water or acid and stored in the dark at

ambient temperature in a tightly sealed container. Obviously there are few prop-

erly prepared and stored drug samples in the illicit marketplace. As a result, some

degradation over time is common for illicitly produced heroin, in particular when

it is the free base, as the base is less stable than the hydrochloride salt. However,

for high-purity illicit heroin samples the rate of degradation (hydrolysis) is so slow

that it can be difficult to measure year-to-year. 

The analyst does need to exercise care in order to avoid hydrolysis of the

heroin when performing impurity profiling analyses. For instance, the hydrolysis

rate for heroin is markedly increased at extremes of pH (e.g. pH < 3 and > 10)

and as a result such routine tasks as liquid-liquid extractions need to be performed

carefully. Gas chromatography (GC) is an analytical tool frequently used in impu-

rity profiling and it can also result in hydrolysis of heroin and/or the trans-esteri-

fication of co-injection compounds. These problems are not limited to heroin,

since most esters are more or less subject to these reactions, as is evidenced by

the well known formation of O6MAM when morphine and aspirin are dissolved

in methanol and co-injected into a gas chromatograph. It is for these reasons that

GC methods utilizing direct dissolution into an injection solvent may not provide

as rigorous a result as do impurity profiling techniques that incorporate a deriva-

tization step. The previous two paragraphs apply equally to illicit cocaine. 

GC analysis of heroin without the use of a derivatization step will result in

the formation of three injection port artefacts. One of these compounds has not

been identified (MW = 381), while the others are 15,16-didehydroheroin [34] and

O

6

-monoacetylmorphine. An injection of a heroin sample, in the absence of a



derivatization step, will nearly always result in the production of some quantity


16

Methods for impurity profiling of heroin and cocaine

of O


6

-monoacetylmorphine in the injection port, where the amount so produced

is a function of injection port temperature and the quantity of activation sites with-

in the injection port. The unknown compound and 15,16-didehydroheroin* are

usually observed at trace levels (< 0.2% relative to heroin) and chromatograph

immediately after heroin on a 100% methylsilicone column. The presence of either

of these two compounds at a level greater than 0.2% relative to heroin may sug-

gest the need for injection port maintenance.



2.

Methods for the determination of major components

Methods for the determination of major impurities frequently incorporate quan-

tification of the primary analyte, that is, heroin. The remaining components in the

sample may or may not be quantified and, if not, the response of these remain-

ing components is typically set up as a ratio relative to the primary analyte. These

methods are often referred to as screening methods, or ratio methods. In actual

fact nearly all impurity profiling methods are ratio methods. A ratio method is

one where the various components of the sample are separated, generally using a

chromatographic technique, concomitant with the tabulation of response measure-

ments followed by determining the ratios of the response measurements against

either an added internal standard or a common sample component. Major impu-

rity analyses are typically used to eliminate samples from comparison that are

clearly different from other samples under examination or to obtain an indication

of the heroin sample origin, that is, South-East Asia, South-West Asia, Mexico

or South America.**

All of the following methods are equally applicable to heroin base and heroin

hydrochloride, although sample preparation may be different for base and

hydrochloride samples. All methods should be regarded as guidance. In general,

minor modification to suit local circumstances will not normally change the valid-

ity of the results. However, any modification must be carefully validated to ensure

that the results have not been compromised. The analytical chemist should also

be aware that not all methods described below are suitable for all types of heroin

sample and that the probability that the method used provides a correct conclu-

sion can vary significantly depending on both the method employed and the exact

nature of the sample.

*Produced in the injection port from the precursor 

ͬ

16,17


-dehydroheroinium hydrochloride.

**For a description of chemical characteristics of heroin samples from different source regions, 

see the United Nations manual Recommended Methods for Testing Opium, Morphine and Heroin

([6], pp. 8-11).




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