Phone: 800-356-1688 or 814-353-1300
12
A less involvedmethodof cleaning the flow controller is touseaheating jack-
et or heat gun toheat the components of the assembled sampling train,while
purging the systemwithnitrogen.As organic compounds areheated anddes-
orbed from the interior surfaces thenitrogengas sweeps themoutof the sam-
pling equipment.
Preparing theCleanPassiveSamplingTrain forRe-use
After the sampling train components have been cleaned, reassemble the sys-
tem, check for leaks, set thedesired flow rate, and certify the sampling system
clean. Follow the procedures described previously in this guide. Package the
clean sampling train toprevent contactwith airborne contaminants.
VIII.Cleaning theCanister
Every air sampling canister,whether newor previouslyused,must be cleaned
and certified before it is used for sampling. Some laboratories batch test and
certify canisters, inwhich after cleaning, one canister out of 10 is tested and
certified clean. We recommend certifying each canister clean prior to use,
however, especially if there is potential for litigation.
Formanyyears therehasbeenmuchdiscussionas towhat constitutes aprop-
er procedure for cleaning canisters. US EPAMethod TO-14A has provided
guidance, and in the last 5-10 yearsmany automated commercially available
canister cleaning systems have evolved. Unfortunately, because these systems
are quite expensive, and some designs have limitations,many analysts design
theirown systemsandmethodologies forcleaningcanisters.Thecleaningpro-
ceduredescribed in this section is apractical approach thatwill ensure canis-
ters are suitably cleaned for ambient air sampling, whether you are using a
commerciallyavailablecleaning systemor a systemof yourowndesign.There
are minor differences when cleaning SilcoCan™ or SUMMA® canisters.We
will discuss these differences in this procedure.
AirVersusNitrogen
The two gases recommended for cleaning canisters are humidifiedultra-high
purity air and ultra-high purity nitrogen. The water in the humidified gas
hydrolyzes impurities in the canister and, according to theory,will occupy the
active sites on the interior surface, displacing the impurities and allowing
them tobe removed.Air is recommendedwhenoxidationof the interior sur-
face isdesired.Theoxygencontentof air,21%, is sufficient for this surfaceoxi-
dation; it is not necessary tousepureoxygen gas.Nitrogen is equally effective
for cleaning ambient air canisters, but, of course,nitrogenwill not oxidize the
surface of the canister.
HeatorNoHeat
Many user-designed canister cleaning systems do not heat the canisters.
Typically this doesnot create aproblemwhen cleaning canisters that areused
in ambient air collection, but as a safeguardwe recommendheating the can-
isters during the cleaning process.Compounds collected inmost ambient air
samples are in the low ppbv range, and can be removed from a canister by
multiple cycles of pressurizationwithhumidified air or nitrogen followedby
evacuation. If therearehigher concentrationsof contaminants in the canister,
however, heatmight be required to clean the canister satisfactorily.
Beaware that addingheat andhumidifiedgas toacanisterpotentiallycancre-
ate a steampressure vessel. Some commercial cleaning systems incorporate a
pressure release valve to ensure thepressuredoes not exceed thepressure rat-
ingof the canisters.
Aheatingoption canbe added to auser-designed canister cleaning systemby
using anoven, heat bands, insulated jackets, or an infrared source.
HandbookofAirToxics.
Sampling,AnalysisandProperties
This referencebookcontainsphysical andchemical
data for all the chemicals in the National
Toxicology Program’s Chemical Database and all
substances indicated in the US EPACleanAir Act
Amendments.
L. H. KeithandM.M.Walker, CRCPress LLC, 1995, 640pp.,
cat.#21373
