 |
 |
|
|
|
 |
|
|
|
|
|
|
|
What is the proper way to preserve drinking water samples for volatile analysis?
|
Sample preservation requirements depend on the analytical
method selected, such as the following:
- EPA Method 502.2 GC Drinking Water Volatile Aromatics Sample Collection, Dechlorination and Preservation
- If samples contain residual chlorine, and measurements of the concentrations of
disinfecting by-products (trihalomethanes, etc.) at the time of sample collection are desired,
add about 25mg of ascorbic acid (or 3 mg of sodium thiosulfate) to the sample bottle before
filling. Fill sample bottles to overflowing, but take care not to flush out the rapidly
dissolving ascorbic acid (or sodium thiosulfate). No air bubbles should pass through the
sample as the bottle is filled, or be trapped in the sample when the bottle is sealed. Adjust
the pH of the sample to <2, carefully adding one drop of 1:1 HCL for each 20 mL of sample
volume. Seal the sample and shake vigorously for 1 minute.
- EPA Method 524 GC/MS Drinking Water Volatile Organics Sample Collection, Dechlorination, and Preservation
- This method follows the same requirements as Method 502.2 except for the dechlorination
requirements. Method 524 suggests that 25mg of ascorbic acid be added to the sample bottle
before filling. If gases are not to be determined, sodium thiosulfate may be used to reduce
the residual chlorine.
- Federal Register Technical Notes on DW Methods October 1994 - Section IV Mandatory Method
Modifications -- EPA Methods 502.2, Rev. 2.0 (R16), 524.2, Rev. 4.0 (R3), and 551 (R15) in
Sample Acidification
- This Technical Note clarifies that samples must be acidified at the time of collection,
but after they have been dechlorinated. Acidification must not be delayed until the samples
are reviewed in the laboratory. These instructions supersede instructions implied or explicit
that may be contained in the methods.
|
|
|
|
|
|
|
