No Air!

Collection of Volatile Organic Compound (VOCs) Water Samples

One of the most frequent sample types that the lab sees collected incorrectly are Volatile Organic Compound (VOC) samples, and unfortunately these samples must be rejected and recollected.

What are VOCs?

Volatile organic compounds (VOCs) are organic chemicals (containing Carbon) that have a high vapor pressure at room temperature. This high vapor pressure results from a low boiling point, which allows their molecules to evaporate from liquid to gas phase, a characteristic known as volatility.

Examples of VOCs are petroleum byproducts, including fuels such as gasoline and diesel; lighter fluid; fuel additives; solvents such as benzene and toluene; cleaning compounds such as dry-cleaning solution, degreasers, refrigerants and adhesives, just to name a few.

Visit https://www.epa.gov/ground-water-and-drinking-water and https://www.usgs.gov/mission-areas/water-resources/science/volatile-organic-compounds-vocs for more information.

Testing for VOCs

The EPA regulates the concentration of certain VOCs in drinking water, and Public Water Supplies are required to test for VOCs per the Safe Drinking Water Act (SWDA).  However, the EPA does not regulate private wells; private well owners are responsible for the safety of their water.  The MT Environmental Laboratory does this testing for public water supplies, along with offering a VOC screening test for private wells.  This testing looks for about 60 different VOCs.

Sample Collection

The requirement for collecting these sample is that there be no air bubbles inside the filled and sealed vial.  The reason for this is that these chemicals will easily evaporate out of the water sample and into any air within the vial.  Therefore, when the water is measured and tested, these compounds may not be detected, giving a false negative result. 

  1. Remove the aerator or screen from the cold water tap and run the water for several minutes until the water temperature has stabilized. Adjust the flow to about the diameter of a pencil.
  2. Remove the cap from a sample vial, keeping the vial upright to prevent spilling any preservatives. Hold the vial at an angle, pointing away from your face, and carefully fill it until it is nearly full. Be careful not to rinse out any preservative the vial contains.  Carefully complete filling the vial by putting water inside the cap and transferring it one drop at a time to the vial to form a meniscus. Someone holding a vial at an angle under a faucet. A vial filled with water with an arrow pointing to the meniscus
  3. Screw the cap on the bottle.
  4. Invert the bottle, tap against your other hand, and check for air bubbles. If any are present, add additional water to reform the meniscus, re-cap, and check again.a tube with an air bubble showing incorrect and a tube with no air bubble showing correct
  5. Shake the bottle vigorously for 1 minute.
  6. Repeat this procedure for the duplicate sample vial.

Place the samples in a cooler with the Trip Blank(s).  The samples must be chilled to 2-6°C immediately and kept at that temperature.  Keep samples away from direct light and gasoline or other solvent vapors.  Deliver them to the laboratory or ship them by courier or overnight express to the laboratory.  Enough ice or freezer packs must be included to keep the samples at ≤ 10°C, but they must be kept from freezing.