Tedlar bags can be an affordable alternative to Summa canisters. They are used for grab sampling (a form of whole air sampling) to take a "snapshot" of an air sample at a specific point in time; they can also be attached to a pump system to take a weighted sample over time. Tedlar bags are used in the following ways:
|How it works: The bag sits inside a sealed bucket. A small vacuum sucks air out of the bucket, creating a pressure differential. When the bucket valve is opened the bag inflates, filling automatically with air.||How it works: An evacuated bag that comes with handles. To take a sample, open the valve on the bag and carefully pull the handles to inflate the bag by hand. This is a proprietary system that is only available from certain suppliers.||How it works: The bag is connected to a pump which pulls air through the system and into the bag to take a sample. Like Summa canisters, the pump surface needs to be inert, which adds a step in terms of cleaning and setting up the system.|
|Advantages: Affordable. No direct contact with the vacuum; the sample is taken automatically when you open the valve||Advantages: Affordable; inflatable bags run about $40-60 apiece, vs. $100 for the bucket and $1000 for a pump system.||Advantages: Pump systems can be connected to flow controllers to take a sample over time. Good for taking calibrated samples.|
|Cost: $100-200||Cost: $40-60||Cost: $1000 and up|
Once the sample is taken, the bag is removed and sent to a lab for analysis.
- Gives you a "snapshot" of what's in the air around you
- More affordable than Summa canisters
- Can be built with parts from the hardware store (bucket monitor)
- Whole air sample: does not measure particles or biological compounds
- Sulfur compounds may react with metal fixtures or fittings in the sampling bags
- GC-MS testing is more expensive than other types of lab analysis
- Air samples degrade quickly in Tedlar bags (1-3 days). Depending on where you are taking your sample, you may need to use rush shipping to get it to the lab in time to analyze it
- Sample bags are sealed and may explode in depressurized cabins (airplanes)
This post is part of the Bucket Monitor project.
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Image credit UBC Micrometeorology CC-BY 2.0
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