13/08/2007 00:00:00
Something in the air, man
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Marijuana continues to be smoked all over the world, despite new health
warnings regarding its effects on the body. A study published this year
found that smoking one joint can restrict the air flow to the lungs by
as much as five cigarettes, while long-term pot smokers also develop
asthma and bronchitis symptoms and excessive lung inflammation.
Marijuana use also increases the risk of becoming psychotic. However,
emphysema is uncommon, unlike with cigarette smokers.
Despite its widespread enjoyment, marijuana smoking is banned in many
countries, although you would not think so walking along streets in the
major cities of western Europe where its characteristic odour pervades
the air. It is relatively easy to confirm that an individual has been
smoking the drug with established tests for blood, urine, saliva and
hair. They detect the principal psychoactive component
DELTA9-tetrahydrocannabinol (THC) and its metabolites by immunoassay or
mass spectrometric analyses (GC/MS and LC/MS).
In some countries, marijuana is smoked in private rooms tucked away in
entertainment buildings. In Taiwan, these are often in karaoke clubs
where customers gather to smoke mixed marijuana and tobacco leaves.
Although it is a fairly common practice, the police appear to be having
some difficulty in catching the smokers red-handed. During raids they
are finding that the culprits have fled, leaving an empty room with no
physical evidence of marijuana except for the smell in the air.
The word of a policeman in court carries some weight but it is much
stronger when backed by forensic data. So the police authorities in
Taiwan approached researchers from the Central Police University and the
National Tsing Hua University to devise a test for marijuana in indoor
air. The team, led by senior reporter Chung-Yen Pai decided to test for
THC, since earlier reports confirmed that this compound survives in
indoor air.
The first step was to find a reliable sampling device. The researchers
rejected several devices that had been used for environmental smoke
because they were deemed insufficiently cheap for routine forensic use
and too complicated to operate in the field. They settled on a
commercial personal air sampler pump and attached an adsorbent tube
packed with Tenax-TA. Samples were collected at 100 mL/min over 2 min.
For analysis, the tubes were detached and placed in the desorption
chamber of a GC injector and heated to release the trapped volatile
compounds. They were analysed by GC/MS with electron ionisation in
selected ion monitoring mode, using the GC retention time and three
characteristic ions (at m/z 314, 299 and 231) for THC confirmation. The
fragment at m/z 231 was used for quantification.
The THC in air from the illegal indoor smoking rooms is usually mixed
with tobacco smoke, so the team had to confirm that THC was detectable
in this atmosphere. The top 20 compounds found in the smoke of tobacco
and marijuana leaves contain 14 common to both plants. Significantly,
THC is a small but clearly visible peak in the total ion chromatogram of
marijuana smoke that is absent from cigarette smoke. For mixtures of
marijuana and tobacco leaves in ratios of 1:1 to 1:15, THC could be
detected in the air after all were smoked, except for the most dilute
samples.
The amounts of THC varied in marijuana smoke from 15 confiscated plants,
ranging from 8.2-1386.7 µg/m3. These variations are probably caused by
the fact that the leaves were from different cannabis species.
With detection and quantification limits of 100 and 125 ng/m3,
respectively, and a linear calibration range of 0.125-50 µg/m3, the
method was applied to air collected from a karaoke bar suspected of
marijuana smoking activity. Four smokers had been in a closed,
air-conditioned room for about 1.5 h before the police raid but all
escaped with their evidence. The air around a couch and table was sampled.
THC was detected in the air at 12.77 µg/m3, which was equivalent to
about 300 mg of marijuana leaves being smoked. The strongest peak in the
ion chromatogram originated from nicotine, confirming that cigarettes
were also smoked.
Positive results like this, that confirm marijuana smoking, can be used
to support further action by the police, such as applying for search
warrants and arresting suspects. Thereafter, standard testing of
biological fluids will establish personal use. With full validation, the
method could be used to provide evidence in court.
http://www.spectroscopynow.com/coi/cda/detail.cda?id=16877&type=Feature&chId=4&page=1
Source:
http://www.ukcia.org/news/shownewsarticle.php?articleid=12785
Author:
Spectroscopy Now via UKCIA
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