12
•
800-356-1688
CleaningMethod
1. Connectall canisters to thecleaning system, then releaseanypressurewithinanyof the
canisters.
Applyvacuum to the system toevacuate thecanisters.USEPAMethodTO-14A/15 rec-
ommendsevacuating the system to50mTorr for1hour, buta reducedpressureof -23
to -25 "Hg is sufficient forgeneral cleaning.
2. After thecanistershavebeenundervacuum forapproximately1hour, pressurize the
canisterswithhumidifiedairornitrogen*. Pressurizationwill dilute the impuritiesand
themoistairwill hydrolyze them.
Pressurizecanisters to5psig if theywillbeheated, or to30psig if theywillnotbeheated.
Proceed to step3when the systemhasequilibratedat thedesignatedpressure.
3. Heat thepressurizedcanisters to120–250 °C, dependingon the typeof valveon the
canisterbeingcleaned.Differentvalveshavedifferent temperature limits; consult the
manufacturer specifications for yourvalve type.Manycommercial cleaning systems
avoid thisconcernbyensuring thevalve isnotwithin theheatedzone.Thecanister
below thevalve isheatedbut thevalve receivesonly radiantheat.
Heat thecanisters filledwithhumidifiedair/nitrogen forat least1hour.
4. Re-evacuate thecanisters to remove thedesorbed impurities.
Allow thecanisters toequilibrate for1hour.
5. Determine if thecanistershavebeencleanedeffectivelyby followingtheprocedure in
CertifyingtheCanister
(p.13).USEPAmethodsrecommendtestingeverycanisteruntila
reliableprocedure isdeveloped.
Repeat steps1–5asnecessary; thenumberof cycleswill bedeterminedbyhowdirty
thecanistersareandhoweasily theyarecleaned.
We recommenddevelopingacleaningprocedure thatmatchesyour specific sampling
procedure, by testing thecanisters for cleanlinessaftereachcycleanddetermining the
numberof cyclesnecessary forproper cleaning.
If thecanistersarenotheated, thenumberof cycles required toclean thecanisters
mightbehigher.
6. Onceacanister isclean, prepare it for collectinga samplebyevacuating it to10–50
mTorr. If your system is leak-tight, youcando thisbyusinga roughingpump.
Manycommercial systems includeamoleculardragpump to reach final vacuumquickly.
*If you are cleaning any fused silica lined canisters, andwill be using heat, use humidified nitrogen, not air.
Cleaning any fused silica lined canisterswith humidified air and heat above 80 °Cmay damage the fused silica surface,
resulting in reduced recoveries of sulfur and other reactive compounds.
Website :
E-mail :
TelNo : 03 9762 2034 . . . inAUSTRALIA
