STACK SAMPLING 1113
The EPA Test Method 16B and the other methods
incorporated by reference contain instructions, along with a
list of references. These should be read in detail before the
Method is attempted. As with all of these methods, testing
should be performed only by trained and experienced person-
nel using equipment and materials designed for this purpose.Test Method 17Test Method 17 is used for the measurement of particulate
emissions from stationary source using an in-stack filter. In
this method, unlike Method 5 in which the filter housing is
maintained at 250 25ºF, there is no control of the filter tem-
perature. This is important since particulate matter is not an
absolute quantity, but dependent on the temperature at which
it is measured. For example, some hydrocarbons are solids at
the Method 5 standard temperature, but would not be solid at
a stack temperature of 400ºF. However, controlling the tem-
perature of the filter can be difficult. Therefore, when par-
ticular matter is known to be independent of temperature, it
is desirable to eliminate the glass probe liner and heated filter
system necessary for Method 5 and to sample at the stack
temperature using an in-stack filter. This method is intended
to be used only when specified by the applicable regulation
and only within the applicable temperature range. Except for
the filter, this method is very similar to Method 5.
The EPA Test Method 17 and 5 write-ups contain detailed
instructions, along with a list of references. They should be
read in detail before the Method is attempted. As with all of
these methods, testing should be performed only by trained
and experienced personnel using equipment and materials
designed for this purpose.Test Method 18Test Method 18 uses gas chromatography (GC) to determine
the identity and concentration of organic compounds emit-
ted from stationary sources. This method is based on the
ability of a material in a GC column to separate a mixture
of gaseous phase organic mixtures into its component com-
pounds. An appropriate detector must be chosen to provide
a response when a compound of interest passes through it.
A chart recorder provides a plot of detector response versus
time. When a compound separated by the column passes
through the detector, the signal increases from the baseline
to a maximum then returns to the baseline; this is called a
peak. The time from when the mixed sample was injected
to the time of maximum peak height is the retention time.
The compounds are tentatively identified by comparison
of the retention time with that of known compounds. The
components are then quantified by comparison of the peak
height with that of known concentrations of the identified
compound.
There are many variables in gas chromatography,
making the GC a very versatile tool. However, these param-
eters require careful selection to provide the necessary sepa-
ration and quantification. They include: column material,column temperature, column packing material, carrier gas
glow rate, injection port temperature, detector type, detector
temperature, etc.
A presurvey is necessary before the actual sampling to
determine the VOCs present and their approximate concen-
tration. A presurvey sample is collected in an evacuated glass
flask, purged through a glass flask, or collected in a tedlar
bag. The sample containers are then heated to duct tempera-
ture to vaporize any condensed compounds. The optimum
chromatographic conditions for separation are determined.
If any peaks are not identified by comparison with known
samples, other techniques such as GC/mass spectroscopy
can be used for identification.
Based on the presurvey analysis, calibration standards
are prepared. There should be at least three standard con-
centrations bracketing the expected concentration for each
compound found during the presurvey. A calibration stan-
dard may contain more than one compound.
The final sampling can take four forms: integrated bag
sample, direct injection, diluted interface sampling, and the
adsorption tube procedure. For the integrated bag sample,
a tedlar bag is placed in a rigid container then filled by
evacuating the container. This sucks sample gas into the
bag, eliminating the possibility of contamination or absorp-
tion by a sampling pump. The bag should be heated to the
source temperature before analysis. The contents of the bag
are flushed through a heated gas sample loop on the GC.
An automated valve injects the contents of the loop onto the
chromatographic column. The resulting peaks are identified
by retention time comparison and quantified against the pre-
pared standards. Bags should be analyzed within two hours
of collection.
The direct injection technique does not permit inte-
grated sampling, however it does eliminate the possibility of
adsorption or contamination by the bags. All sampling lines
must be maintained at stack temperatures to prevent conden-
sation. The sample is sucked directly through the gas sample
loop. Analysis is the same as for bag samples.
The dilution interface sampling and analysis procedure
is appropriate when the source concentration is too high
for direct injection. The stack gases are diluted by a factor of
100:1 or 10:1 by the addition of nitrogen or clean dry air.
Adsorption tubes can be used to collect organic com-
pounds from stack gases. The selection of the adsorben
is based on the chemicals present in the stack gas. Once
a known volume of gas has been drawn through the tube
the tube can be taken back to the laboratory for analysis.
Tubes can generally be stored up to a week by refrigerat-
ing a sample. Once back at the laboratory, the adsorbent is
extracted with suitable solvent and the solvent analyzed by
GC. There are many variables that affect the efficiency of
the tube for collecting representative samples. The quanti-
tative recovery percentage of each organic compound from
the adsorbent material must be known. When the adsor-
bent capacity of the tube is exceeded, material will break
through the tube and not be collected. This is dependent on
the sample matrix, i.e. the amount of moisture and the effect
of other compounds competing for the adsorbent.C019_003_r03.indd 1113C019_003_r03.indd 1113 11/18/2005 11:07:17 AM11/18/2005 11:07:17 AM