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• Monitor Integrated Sampling Progress: It is a good idea to monitor the progress of the inte- grated sampling during the sampling interval. The volume of air sampled is a linear function of canister vacuum. For example, halfway (4 hours) into an 8-hour sampling interval, the canister should be half filled (2.5 L) and the gauge should read approximately 17 in. Hg. More vacuum than 17 in. Hg indicates that the canister is filling too slowly; less than 17 in. Hg and the canister is filling too quickly. If the canister is filling too slowly, a valid sample can still be collected (see Section 3:2.4). If the canister is filling too quickly because of a leak or incorrect flow controller setting, corrective action can be taken. Ensuring all connections are tight may eliminate a leak. It is possible to take an intermittent sample. The time interval need not be continuous. • Avoid Contamination: Flow controllers should be cleaned between uses. This is normally accomplished by returning them to the laboratory. For large air sampling projects, Air Toxics Ltd. has designed a field conditioning program for 24-hour flow controllers involving a purge manifold. This arrangement provides the sampler with scheduling flexibility, inventory control, and convenience in the field. Air Toxics Ltd. will provide the 24-hour flow controllers, a purge manifold, Teflon tubing, rubber ferrules, vacuum pump, and flow meter. The sampler will need to provide the certified nitrogen cylinder and the certified high pressure regulator. Call Client Services at 800-985-5955 if you are interested in the field conditioning program. • Keep Sampling Train Out of Direct Sunlight: The sampling train should be kept out of direct sunlight during sampling. There will be some minor flow rate drift if the temperature of the controllers is allowed to vary significantly. 3.2.6 Step-by-Step Procedures for Integrated Sampling These procedures are for a typical ambient air sampling application and actual field conditions and procedures may vary. Before you get to the field: 1. Verify contents of the shipped package (e.g., chain-of-custody, canister, particulate filter, and flow controller). 2. Verify initial vacuum of canister. When ready to sample: 3. Remove brass cap. 4. Attach flow controller to canister. 5. Open valve 1/2 turn. 6. Monitor integrated sampling progress periodically. AIR TOXICS L I'D. __ 14