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So if a sample of an illegal drug is
seized in a raid or is discovered being
smuggled at an airport, and the
investigators find for instance,
a white powder, how do they detect and
identify the illegal drugs?
Well, there's a number of chemical tests
that can be done, and these are
based on treating the unknown sample with
chemical reagents and looking for
particular colour changes.
For instance, the Marquis test gives a
red-purple
colour for heroin, and orange-brown colour
for amphetamines,
while the Scott test gives a blue colour for
cocaine.
But as we know from the lecture on
identifying particular compounds,
we really have to turn to chromatographic
and
spectroscopic methods to really prove what
these compounds are.
For instance, we can use thin layer
chromatography,
which we talked about in the earlier
lecture.
But we know that thin layer chromatography
is not very precise,
and if it's used can only ever be a
presumptive test.
What we need to do is to use more
sophisticated instrumentation,
the more sophisticated chromatographic
methods that we talked
about earlier, for instance, gas
chromatography and HPLC.
For identification of the compounds after
the chromatographic separation, we
would use
the infrared, and particularly looking at
the fingerprint region of the infrared
spectrum.
Then, the other technique for
identification
we can use is mass spectrometry.
And as you saw in that earlier lecture, we
can combine mass spectrometry with gas
chromatography and do GC-MS.
One of the ways that is used to detect and
identify
a drug in a body fluid such as urine, is
called immunoassay.
And this involves generating antibodies to
the drug
and setting up the immunoassay in such a
way that when the substrate, for instance,
cocaine or amphetamines or morphine,
binds to the antibodies, this chemically
triggers a colour change.
And that colour change can be very quickly
and simply observed by the investigator.
Well these techniques, the immunoassay
techniques have come in for a
certain amount of controversy, partly
because
of their very, very high sensitivity.
Perhaps that sensitivity can be too high,
and if not used properly, can give very
misleading results.
For instance, morphine.
There are immunoassays available for the
detection of morphine in urine.
So the assumption would be, that if
someone tests positive
using this method, then they must be a
heroin user.
But it's not necessarily so.
Morphine is produced by the plant papaver
somniferum,
and this is one of the poppy family.
It turns out that almost all poppies
produce morphine,
but all the other types of poppy produce
it in very tiny amounts.
And poppy seeds of course
are used to flavour for instance bakery
products, such as a poppy seed bagel.
So if somebody eats a poppy seed bagel,
there
will be trace amounts of morphine in their
system.
Not sufficient to have any effect,
but if the immunoassay test is not done
properly,
it can be sufficient to give a positive
result.
So someone may be condemned
as a drug user, whereas, actually, they
just had a poppy seed bagel for breakfast.
So, if we sum up what we've learned in
this lecture, there are three types of
illegal drugs.
Natural compounds, which are extracted
directly
from the organism that produces them,
such as morphine, cocaine and cannabis.
There are semi-synthetic compounds which
are obtained by chemical
modification of those natural compounds;
an example would be heroin.
And then there are the purely synthetic
compounds which are
made by chemical means, and an example
would be ketamine.
All of these can be detected and
determined using the techniques of
spectroscopy and chromatography that we
learned about in our earlier lecture.
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