Methods for impurity profiling of heroin and cocaine

6

Methods for impurity profiling of heroin and cocaine

Impurity profiling applications fall principally into one of two overlapping

categories. They are tactical (evidential/judicial) and strategic (intelligence). An

example of a tactical application of impurity profiling is the establishment of dis-

tribution and/or trafficking links between multiple seized samples that have been

obtained at different locations or in the possession of different individuals. Strategic

uses can include the identification of synthesis methods utilized in clandestine lab-

oratories, the identification of chemicals, reagents and/or solvents employed by

those laboratories and, for drugs derived from botanical sources, a scientifically

defensible determination of the geographical origin of the sample.

In order to successfully apply impurity profiling results, all parties involved

need to understand both the goals and the limitations of the technique. First and

foremost, it must be understood that drug impurity profiling is not a stand-alone

technique, but rather a scientific approach that complements law enforcement

investigative information. A necessary requirement for the successful implemen-

tation of this work, therefore, is an information exchange mechanism that allows

continuous feedback between laboratory and law enforcement personnel. Not only

must the forensic chemist be very familiar with the chemistry of all target ana-

lytes, he or she must also fully understand the purpose of the investigation in

order to select the most appropriate analytical approach and interpret the results

correctly. 

The value of the analytical data obtained using impurity profiling procedures

is limited by several considerations, principal among them the limits imposed by:

(a)

The quality of the samples under investigation;

(b)

The quality of the information provided by law enforcement personnel;

(c)

The extent of the analyst’s knowledge of the relevant analytical and syn-

thetic (drug processing) chemistry;

(d)

Uncertainties arising because clandestine processing techniques and traf-

ficking practices are often not well known;

(e)

The availability and quality of a database of analytical results.

Nevertheless, and despite these limitations, drug impurity profiling studies can be

a valuable tool in support of operational investigations by law enforcement agen-

cies and are used successfully for that purpose.

B.

Analytical implications of heroin and 

cocaine manufacture and supply

1.

Determination of origin

The first and absolutely necessary prerequisite for the successful implementation

of any drug origin determination programme is the acquisition of relevant data sets

derived from drug samples obtained from all known sources. Such a compilation

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Aspects of drug characterization and impurity profiling

7

is generally referred to as an “authentic database”. Obviously the acquisition of

these authentic database samples directly from the growing fields and directly

from the illicit laboratories is a difficult, dangerous and costly task that in general

constitutes a primary impediment to creating a successful origin determination

programme for any illicit drug. 

For drugs derived from plant sources it is most often possible to assign geo-

graphical origin, if at all, in only the most tentative sense when the analytical

technique employed exclusively targets the major alkaloids. However, there are

notable exceptions, perhaps the most notable being those heroin samples originat-

ing in South-East Asia. The relative ratios of the alkaloids present in the major-

ity of South-East Asian heroin samples are distinctly different from those found

in heroin samples originating in other source regions. As a result, many South-

East Asian heroin samples can, with reasonable certainty, be distinguished from

those samples originating elsewhere simply by comparison of major alkaloid

analyses. On the other hand, many samples of highly refined heroin from South-

West Asia are impossible to distinguish even tentatively from heroin from South

America using only major alkaloid data. 

Fortunately, analyses of minor alkaloids, processing by-products and occlud-

ed solvents provide powerful and useful tools for both the determination of sam-

ple origin and trafficking links. Those laboratories fortunate enough to have the

capability of trace element and isotopic abundance analyses have two additional

powerful tools that are also applicable to both of these tasks. The abundances of

carbon

13

, oxygen

18

and nitrogen

15

(relative to the most abundant isotope) are a

complex interplay between latitude, altitude, the underlying sources for the target

elements and the overall biological fractionation events of the different isotopes

[8-13]. On the other hand, trace elements present in clandestine samples arise

almost entirely from inadvertent contamination of the sample from a myriad of

possible sources to even include the remote possibility that some of the contam-

ination is related to the soil in which the drug crop was cultivated. For both iso-

topic abundance and trace elemental analyses, proper interpretation of the

analytical data requires that the analyst have an in-depth understanding of the rel-

evant physical, chemical and biochemical principles. 

The analysis of trace elements using inductively coupled plasma-mass spec-

trometry (ICP-MS) has also been employed for sample comparison studies.

Additional criteria for the classification and the comparison of heroin samples

have been developed using ICP-MS to screen 96 samples of known geographical

origin for 35 elements [14]. The limitations of this approach arise from non-homo-

geneity of illicit heroin samples, from the lack of an appropriate database and

from those contaminations which are typically introduced through the addition of

cutting agents. At present there is a very limited understanding of the relation-

ships that may exist between the various observed elemental compositions versus

geographical origin, processing in the source areas and the process of cutting. 

Relative alkaloid ratios within samples are most closely associated with plant

varietal differences and, to a lesser extent, agronomic differences. An even more

important influence on the relative ratios of all alkaloidal constituents, to include

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