3.1.1 Delete (dry ice is not required).
4.1.1 Model 90 and model 75 flow meter calibration. The model 90 sample pump
inlet is attached to the outlet of the model 75 oven. Air is passed through the system at
the rate that will be used in sampling and for the total volume anticipated to be
sampled. If the flow meters on the 2 instruments do not agree within 0.01 liters,
then adjust the meter on the model 90 until agreement is within 0.01 liters. After
making any correction, run a full calibration again.
4.1.2 Sample train assembly. Assemble the probe (prefilter if needed), adsorber
tube, and teflon line to the inlet of the model 90. Attach a short (8 to 10 inches)
flexible line to the outlet of model 90. Have a completely clean evacuated tedlar
sample bag nearby for collection of sample to be analyzed.
4.1.3 Pretest leak check. Stopper the inlet of the probe and place the flexible tube
on the outlet of the model 90 in a small open container of water. Turn on the sampling
pump. For a satisfactory leak check, bubbling should cease within 1 minute. If the leak
check is unsatisfactory, tighten the fittings or change parts until a satisfactory leak
check is obtained. 4.1.4 Sampling train operation. Place the probe and the front portion
of the adsorption tube in the stack. If the stack has a temperature higher than ambient,
allow time for the probe to heat before starting the sample pump. Start the model 90
pump and adjust to the desired flow, usually about 90 ml/min. After about 0.1 liter
of sampling, or equivalent to the volume of air that is displaced in the sample system
before the flowmeter, remove the flexible tube from the outlet of the model 90 and
install the evacuated tedlar bag. This assures that gaseous components are undiluted by
the air originally in the sampling system. Record requested data on the data form during
the sample time. The sampling is usually done for 1 hour with a total of 5 to 6 liters
sampled. When sampling is complete, record the precise volume sampled. The
process may require different sample times or sample volumes. (Sampling form is
4.1.5 Post test leak check. Remove the tedlar bag and replace it with the flexible
tube. Stopper the probe and operate the same as the pretest leak check specified in
section 4.1.3. If the leak test is not acceptable, invalidate the sample.
4.2 Sample recovery. The tedlar bag is ready for direct analysis on the GC. The
adsorber tube shall undergo the following 2-stage preparation:
4.2.1 Sample purge. The absorber tube is placed in the Byron model 75 oven
with a clean tedlar bag attached directly to the tube. A volume of clean dry air is
passed through the adsorber tube while holding the oven temperature at about 130
degrees Celsius. The volume of air should be precisely the same as that sampled.
This purge is necessary to remove any CO2 on the sample tube, and the elevated
temperature is needed to assure CO2 removal from any absorbed water. The tedlar
bag is now ready for direct analysis on the GC.
4.2.2 Sample digest. The absorber tube, now free of CO2 and the lighter NMOs,
is now attached to an oxidation catalyst, and another tedlar bag is attached to the outlet
of the oxidation catalyst. A volume of clean dry air equal to that sampled is passed
through this system while the temperature on the sample tube is brought up to 600
degrees Celsius. If the sampled volume was less than 3 liters, a larger volume shall be
used in the digestion to assure completion. Usually a multiple of precisely 1.5 or 2.0 of
the sampled volume is sufficient. This third tedlar bag is now ready for direct analysis
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