7
To set the desired flow rate follow these steps:
1. Remove the protective cap from the back of the Veriflo™ Flow Controller
SC423XL body.
2. Connect either an evacuated canister or a vacuum source to the outlet of
the sampling train.
3. Connect a high quality calibrated flow meter (i.e., mass flow meter,
rotameter, GC-type flow sensor, e.g., Restek Flowmeter 6000, cat. #21622)
to the inlet of the train.
4. Apply vacuum by opening the canister or turning on the vacuum source.
5. With a 3mm hex (Allen) wrench, adjust the piston gap screw to achieve
the desired flow rate (Table 2). Between adjustments allow the flow to
equilibrate for several minutes.
6. Replace the protective cap onto the back of the Veriflo™ Flow Controller
body.
Cleanliness: Certifying the Sampling Train for Use
US EPA Compendium Method TO-14A/TO-15 requires that the sampling
train be certified clean prior to use. Certify the train by passing a humidified,
high-purity air stream through the train, concentrating the exit gas on a trap,
and analyzing the gas by gas chromatography / mass spectroscopy or other
selective detector. For the sampling train to pass certification the analytical sys-
tem should not detect greater than 0.2ppbv of any target VOC.
The certified sampling train should be carefully packaged in aluminum foil or
in a clean container for storage or for shipment into the field. Care in packag-
ing is critical. Careless handling could affect the preset flow rate. When the
sampling train is ready for sampling, prepare the canister.
IV. Preparing the Canister for Sampling
Preparing a canister for sampling involves certifying the canister clean, evacu-
ating the canister to final pressure for use, and identifying the canister. All
information acquired during these processes is needed for the chain of cus-
tody.
Certifying the cleanliness of the canister is important toward ensuring that
results reported are solely from the site sampled, and not admixed with residue
from a previous site or from contaminated laboratory air. To certify a canister
clean, fill the canister with humidified air, pass the air from the canister
through an adsorbent trap and analyze the adsorbent for target VOCs by
GC/MS or other selective detector. Two US EPA methods discuss canister cer-
tification: EPA Compendium TO-12 and EPA Compendium TO-14A/TO-15.
To comply with EPA Compendium Methods TO-14A/TO-15, the analytical
system should not detect greater than 0.2ppbv of any target VOC. To comply
with EPA CompendiumMethod TO-12 the analytical system, GC/FID, should
not detect greater than 0.02ppmvC hydrocarbons. Although batch certification
of canister cleanliness is a relatively common practice, we recommend certify-
ing and documenting each canister individually. Detailed cleaning instructions
are presented in Section VIII. Cleaning the Canister (page 12).
Figure 6
Conventional vacuum gauge
and high-accuracy test gauge.
Table 2
Flow rates for integrated sampling, using a 6-liter canister
and sampling on the flat portion of the flow curve for the flow
controller (Figure 5).
Sampling Period
(hours)
0.5
0.75
1
2
4
8
12
16
24
Flow Rate Range
(mL/min.) 133-167 89-111 67-83 33-42 17-21 8-10 5.6-6.9 4.2-5.2 2.8-3.5
Collected volume is 4-5 liters (flow = volume in mL / sampling time in min.).
