0046im.jpg)
Guide for Characterization of Sites Contaminated with Energetic Materials
39
B. WATER EXTRACTION BY SALTING OUT
Low-Level Method (salting-out extraction)
1. Add 251.3 g of sodium chloride to a 1-L volumetric flask (round). Measure
out 770 mL of a water sample (using a 1-L graduated cylinder) and transfer it to
the volumetric flask containing the salt. Add a stir bar and mix the contents at
maximum speed on a magnetic stirrer until the salt is completely dissolved.
2. Add 164 mL of acetonitrile (measure with a 250-mL graduated cylinder)
while the solution is being stirred and stir for an additional 15 minutes. Turn off
the stirrer and allow the phases to separate for 10 minutes.
3. Remove the acetonitrile (upper) layer (about 8 mL) with a Pasteur pipette
and transfer it to a 100-mL volumetric flask (round). Add 10 mL of fresh aceto-
nitrile to the water sample in the 1-L flask. Again stir the contents of the flask for
15 minutes followed by 10 minutes for phase separation. Combine the second
acetonitrile portion with the initial extract. The inclusion of a few drops of salt
water at this point is unimportant.
4. Add 84 mL of salt water (325 g NaCl per 1000 mL of reagent water) to the
acetonitrile extract in the 100-mL volumetric flask. Add a stir bar and stir the
contents on a magnetic stirrer for 15 minutes, followed by 10 minutes for phase
separation. Carefully transfer the acetonitrile phase to a 10-mL graduated cylin-
der using a Pasteur pipette. At this stage, the amount of water transferred with the
acetonitrile must be minimized. The water contains a high concentration of NaCl
that produces a large peak at the beginning of the chromatogram, where it could
interfere with the HMX determination.
5. Add an additional 1.0 mL of acetonitrile to the 100-mL volumetric flask.
Again stir the contents of the flask for 15 minutes, followed by 10 minutes for
phase separation. Combine the second acetonitrile portion with the initial extract
in the 10-mL graduated cylinder (transfer to a 25-mL graduated cylinder if the
volume exceeds 5 mL). Record the total volume of acetonitrile extract to the
nearest 0.1 mL. (Use this as the volume of total extract [Vt] in the calculation of
the concentration after converting to L). The resulting extract, about 56 mL, is
then diluted 1:1 with organic-free water (with pH <3 if tetryl is a suspected
analyte) prior to analysis.
6. If the diluted extract is turbid, filter it through a 0.45-mm Teflon filter using
a disposable syringe. Discard the first 0.5 mL of filtrate and retain the remainder
in a Teflon-capped vial for RP-HPLC analysis, as in Sec. 7.4.
Previous Page
