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Drug Testing News
HOW GC-MS Drug Testing WORKS
by Nicholas Coffey, Chemist
People who routinely rely on drug testing results are largely
unaware of the
problems inherent in such tests. If the tests are used in a
holistic
informational context, with other indications of abuse being
considered they
may be more useful. However, reliance on GC-MS as 100%
reliable is
misguided at best. Why? The best way to appreciate the
limitations of the
GC-MS is to understand how it works.
The GC-MS is a hybrid of two technologies: the gas
chromatograph and the
mass spectrometer. The gas chromatograph is a device for
separating a
mixture of compounds according to their relative attractions
to a substrate
material called an adsorbent. Typically the adsorbent is
silica or alumina
gel lining in column inside the machine. The sample is
injected into a
stream of carrier gas inside the machine where it goes through
the column
which is heated by an oven. The separations occur on the
column. The
stream of compounds, now, in theory separated, pass by a
detector which
causes a signal to be emitted. This signal is usually picked
by and
electro-mechanical device to record it. It's important to
understand
that what is recorded is the relative retention times of the
compounds on
the column in the machine. There is no information about the
chemical
structure of the materials being recorded.
After separation on the column in the GC, the materials then
pass through to
the mass spectrometer. In this machine the materials are
destroyed in the
presence of a strong magnetic field. Fragments of the
materials are then
analyzed according to their molecular weight. The results are
compared
against databases which are built on the statistical
likelihood of
particular compounds to fragment in specific ways. Again,
there is never a
direct analysis of the material. The precision and accuracy of
the results
depend on the quality of the database used.
Thus false positives for opiates are common in patients taking
certain
antibiotics because the drug labs don't consider this source
of false
positives. Patients taking levofloxicin and ofloxacin were
given false
positive results four out of five times in tests of the method
and patients
using Cipro were attributed with false positives one in five
times (JAMA,
12/26/01). The problem was that the fragmentation patterns of
antibiotics
weren't in the databases so the next most likely match was
automatically picked by the software.
There are no laboratories currently operating outside of
academic settings
that have GC-MS operated by chemists with sufficient
experience to
analyze unknowns or unfamiliar compounds. Small wonder that.
It takes a
minimum of four years of graduate analytical chemistry and two
years of
medical school training in toxicology to gain the experience
required to
process pharmaceutical unknowns by GC-MS. Drug labs are
typically operated
by technicians who are supervised by a chemist or engineer
with a BS degree.
While these personnel are well trained enough to handle
routine compounds
found in the databases there shouldn't be any question as to
the
possibility of false positives emerging from these settings. A
certain
mystique has arisen about the GC-MS method among drug test
providers and
employee supervisors. The widespread belief in the
infallibility of the
method is wholly unjustified.
Our Note:
Wonderful, at last someone telling the truth, wonder who got
him upset enough
to do this. The gentlemen who invented the GC-MS is from the
UK, it was
invented for the military, pilots and public servants,
however, the insurance
companies got wind of it and then it trickled down to the
private sector.
Parliament was going to pass drug testing in the UK and the
inventor went
back and told them about the accuracy and asked that they not
do to their
people what the American Government has done to us, he made
himself a billionaire at our expense.
