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Field Sampling
This experiment will build on "Smoke
I" by having each student go into the field to sample environmental
tobacco smoke (ETS) with personal air monitoring pumps. To one
of these you will attach 2,4 DNPH impregnated SPE cartridges and
the other XAD-2 glass tube. The former will simultaneously derivitize
and adsorb aldehydes as they are pulled through the cartridge
while the latter will sorb nicotine. The targets of interest
are nicotine, formaldehyde and any other aldehydes that can be
resolved and detected. HPLC will be used to separate the formaldehyde
hydrazone from other interfering compounds and capillary GC with
nitrogen-phosphorous detection to selectively isolate and monitor
nicotine. Methodology
Air sampling.
The nominal sampling rates for the two cartridges are 500 ml/min
for the DNPH SPE cartridge and 1 liter/min for the XAD glass tube.
You will need to calibrate the air pump, in the laboratory, both
before and after you gather your sample by using a bubble meter.
The TAs will demonstrate how to do this and will also give you
some indication as to the total amount of air needed for the available
detection limits attainable with the instruments in the lab; typically
a sampling time of 1 hour at the above flow rates yields detectable
signals.
Location.
The purpose of this section VI is for you to carry out the sampling
of polluted air at a location of your choice. Each student group
will have to consider carefully the QA/QC issues involved in obtaining
a representative sample, having appropriate blanks and controls,
and maintaining sample integrity. The sample site should be chosen
carefully to illustrate some hypothesis that is being made. For
example if a smoke-filled bar is chosen for sampling perhaps the
control site would be a smoke-free restaurant. Although tobacco
smoke is likely the only source of nicotine it should be remembered
that there are innumerable sources of formaldehyde (see references
in Smoke I). Make sure to note as much about the sample location
as possible for later data analysis. Analysis. A lab period has been set aside for each group to extract the two analytes from their respective sorbents and measure each using the two chromatographic systems. The SPE cartridge will be eluted with acetonitrile (~5 ml) and diluted to the mark in a volumetric flask. The XAD tube will require a bit more work as there are two sections to the tube. The first and largest amount of XAD is the primary sorbent and you'll need to carefully remove this from the tube into an appropriate container containing the extracting solvent (ethyl acetate); be precise about the final volume of extracting solvent. The shorter section of XAD is the back-up sorbent and is there to indicate whether there was any "breakthrough" of nicotine during the air sampling. Please isolate this separately from the primary sorbent as it will represent a check on the sampling methodology. There, of course, should also have two DNPH cartridges attached to each other to provide the same assurance of no breakthrough but at this time we will not due to cost considerations. Upon obtaining each of the extracts proceed to the analysis step using the appropriate conditions/instruments that you are now familiar with. |
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