10
•
800-356-1688
Procedures used in these chromatographic analyses generally include amulti-
point calibration, using gas standards. Therefore calculations of organic com-
pounds in collected samples are straightforward—only volumes analyzed and
dilution rates are needed to determine sample concentrations. High concen-
tration calibration gas standards are commercially available (e.g., 1 ppmv or
100ppbv).Toprepareanalytical standards, introduceanaliquotof stockmate-
rial into a canister anddilutewithhumidified air or nitrogen.After analyzing
the calibration standards,determine the response factor for eachanalyteusing
the peak area counts per concentration.
After analyzing the multipoint calibration standards and calculating peak
area/concentration response factors, analyze the “real world” samples. If an
“unknown” sample has not been diluted, apply the corresponding response
factor to each“unknown”analyte peak area to get the reporting limit concen-
trationof the“unknown”in the analysis (typically inppbv). If youhavedilut-
ed the canister to get apositivepressure, youmust apply thedilution factor to
theconcentrationvalues.This isdonebymultiplying the reporting limitby the
dilution factor.
VII.Cleaning thePassiveSamplingTrain
The cleanliness of the sampling train is critical to collecting accurate and rep-
resentative samples. Practices followed for cleaning passive sampling equip-
mentbetweenuses range frompurging the samplingpathwaywithhumidified
nitrogenor air formanyhours, toheating thepathwayduring apurge, todis-
assembling each component, sonicating the pieces in solvent (
except for the
critical orifice
), and oven baking the pieces prior to reassembly. The most
suitablemode of cleaningdepends on the concentrations of analytes of inter-
est, and contaminants, in the previous sample collected.
The particle filtermust be thoroughly cleaned betweenuses.Disassemble the
filter, then remove the larger particles from the frit by blowing particle-free
nitrogen through the frit from theoutlet surface toward the inlet surface.After
the larger particles are removed, sonicate or rinse the filter parts inmethanol
and then bake the parts in an oven at 130 °C to remove any residual organic
vapors.
The critical orifice and flow controller can be cleaned in either of two ways.
The firstmethod is to disassemble the flow controller and clean all themetal
partswithmethanol.Thiswill remove anyhighboilingpoint compounds that
have condensedonto thewetted areas of the controller.Heat the cleanedparts
in anoven at 130 °C to remove residual organic vapors.
Donot sonicate the
critical orifice.
Do not sonicate in solvent or bake any of the nonmetallic
parts, such as O-rings, or they will be damaged. Do not rinse the vacuum
gaugewithmethanol.Thevacuumgaugemaybeheated,but donot exceed80
°C; higher temperatures will damage the face and the laminated safety glass
lens. Heating to 80 °Cwill not affect the mechanical operation of the spiral
bourdon tube in the vacuum gauge.
A less involvedmethodof cleaning the flow controller is touse aheating jack-
et or heat gun toheat the components of the assembled sampling train,while
purging the systemwithnitrogen.As organic compounds are heated 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 the desired 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.
frequently
asked
question
Wherecan I findEPA
AirToxicMethods?
pdf filesofUSEPAAirToxic
Methodsareavailableat this
webaddress:
for
more
info
ASTMReferenceD5466Standard
TestMethod forDetermination
ofVolatileOrganicChemicals in
Atmospheres
(CanisterSamplingMethodology)
availableat
Website :
E-mail :
TelNo : 03 9762 2034 . . . inAUSTRALIA
