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X.Conclusion
Awell designed and properly prepared passive sampling system helps ensure accurate, useful information is obtained from an air
samplingproject. In thisguide,wedescribe thecomponentsof the system,procedures for assembling the systemandpreparing it for
sampling, and the samplingprocedure.Cleaning systemoptions andprocedures for cleaning aused sampling train and canister for
certificationprior toa subsequent samplingarealsopresented.The following sectiondescribesRestekproductsdesigned tohelpcol-
lect and analyze air samples.
How toExtendCanister Life
What reduces canisterperformanceand longevity?Leakage is themost common reason for canister failure,but contamination
anddamage to the fused silica lining canalso send canisters to the scrapyardprematurely.Here are some tips toprotect your
investment:
1. Prevent leaks
Useproperhandling toavoid these3 leadingcausesof leaks.
a. Particles in thevalve
Youcanpreventparticles fromentering thevalvebyalwaysusinga2or7µmparticulate filterduringsamplingandonyour
canistercleaningequipment.Also,protect thevalve inletby replacing thebrassdust capwhennot inuse.TheEPA-recom-
mendedmetal-to-metal sealing valves provide the greatest inertness, but tend tobemore sensitive toparticulatedamage
thanothervalve types.
b. Galled thread fittings
Avoid galled thread fittings byusing a gap gauge toprevent overtighteningof compression fittings.Turningonly¼ turn
past finger-tight is another ruleof thumb topreventovertightening.Usebrass compression fittingson stainless steel,dur-
ing nonsampling activities, such as cleaning or calibration, tominimize threaddamage.Galled threadsmay also cause a
poor connection tovacuum/pressure gauges, resulting in inaccuratemeasurement andmisleading conclusion that canis-
ter leakageexists.
c. Overtightenedvalve
Canistervalvesaredesigned toclosesecurelywithhand tighteningonly. Overtighteningavalveclosurewithawrenchmay
damage thevalve seatwhere the seal ismade.
2. Reducecontamination
a. Segregate high concentration (ppm) cans and trace concentration (ppb) cans.Use dedicated canisters, or gas sam-
plingbags, for ppm level sampling, since it is extremelydifficult to remove impurities fromppm sampling to a level
suitable for trace sampling.
b. Clean the entire sampling train as you would the can to minimize introduction of contaminants into a clean can.
Maximum temperature is80 °Con thegaugeand90 °ConRestek’sVeriflo® flowcontroller.
c. High temperature (>100 °C) humidified air (steam cleaning) provides themost effectiveway to remove contamination
fromelectropolishedcans(TO-Can®or SUMMA® canisters), but candamage fused silica lined cans.See#3below for
proper cleaningof fused silica linedcans.
3. Avoiddamagetofusedsilica linedcans
Be sure to followmethod recommendationswhencleaningyour canisters toavoiddamaging the fused silica lining.Cleaning
studiesofSilcoCan®canistersusinghumidifiedairandheatat80°Cand125°Chaveshownreducedrecoveriesof sulfurcom-
pounds,when compared tousingnitrogenunder the same conditions. This irreversible damage is due tooxidationof the
surface, creating active sites thatmay affect the recovery of reactive or polar compounds. Strong acids andbasesmay also
result indamage to the internal can surface.
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