Sampling of environmental water for low level tritium analysis
A. Explanation
Tritium in environmental samples will be determined with a limit of detection, of 0.1 T-units (TU) (0.3 pCi L-1). Rains and water vapor of the open air varies from 2 to 30 TU. Indoors, the atmospheric humidity may reach 10,000 TU from various luminescent dials. Exposure of the water to such air at any temperature might give badly erroneous tritium results.
B. Sample bottles
In the past we recommended using 1 liter. (1 qt.) glass bottles with “PolySeal”, caps for storage and shipping. With today's low tritium levels in outside air this may no longer be necessary. There have always been losses from bottles breaking during shipment. Except for extended storage (years) indoors, we now recommend the use of high density polyethylene bottles, such as U.S. Department of Transportation Spec DOT-2. The bottles should be clean and dry, preferably factory fresh. Please avoid the use of thin-wall milk jug style containers, because they can easily develop leaks during shipping and handling. They must have good caps. Hold a filled bottle upside-down and squeeze hard. No leakage is allowed. Remember that there are large pressure changes in air transport. Pack in sturdy boxes with plenty of cushion material. Camping coolers make excellent shipping containers. (Note: we do not return them, ref II.7).
If you use glass, each bottle should be bubble-wrapped or placed in its own cardboard compartment within the container. Additional packing material such as shredded paper, more bubble-wrap or “peanuts” can be used to fill remaining space. Double boxing with packing in between is also encouraged. Ordinary coolers, used in place of cardboard boxes, provide an extra degree of protection.
If transfer is to be made indoors, the dry bottles should first be filled with argon gas. See below.
C. Sampling procedure
- Sample transfer should be done outdoors, unless a specially vented room is available with ban on wristwatches.
- THE PERSON PERFORMING THE SAMPLE TRANSFER IS NOT ALLOWED TO WEAR A WRISTWATCH, COMPASS OR SIMILAR WITH LUMINESCENT DIALS OR SO CALLED “BETA” LIGHTS.
- Fill the bottle not quite to the neck with sample, leaving a few cm3 of air. Do not rinse. Overflow is not desirable. Replace and screw cap on tightly.
- Record bottle numbers on original field data sheets, and fill in information on bottle label.
- If sampling must be made indoors, never let the water be exposed to the air. Pipe the sample water into the middle of an argon-filled bottle (below the argon level). Do not pour the argon out before, by tilting an open bottle.
- Add nothing to the water sample. Do not filter, preserve or chill in any manner. Avoid freezing which may crack the bottle.
