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
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