BEPOM extraction

Last modified by Xwiki VePa on 2024/02/07 07:36

Step-by-step guides

Filter samples

  1. Prepare a 0.1 N NaOH solution (4 g NaOH + MilliQ in 1 L volumetric flask).
  2. Add 10 mL 0.1 N NaOH solution to each clean 15 ml centrifuge tube containing the POM filter.
    1. I recommend transferring the filter from the tube they were stored in to a fresh tube that has been rinsed with 0.1 N NaOH solution before extraction.
    2. Vortex/shake each centrifuge tube once the NaOH has been added.
      1. Important: make sure the POM filter is completely submerged after the tube has been shaken.
  3. Create 3 blank/control samples.
    1. Add NaOH to 3 cleaned centrifuge tubes that do not contain a filter.
  4. Put a batch of tubes in the refrigerator for 24 h.
  5. Add concentrated HCl to each bottle to adjust the pH=7 using 20-200 µL pipette.
    1. Add 0.1 N NaOH solution to neutralize if pH<7. Record both volumes added.
    2. When I neutralize, I usually add ~ 92 µL of concentrated HCl initially. This will over acidify, but if you immediately add ~100-200 µL of 0.1 N NaOH, it should have a pH of ~ 6-7.
  6. Filter the solution with a 0.2 µm filter and transfer to 25 mL polycarbonate bottles.
    1. Rinse these bottles with MQ or the NaOH solution prior to sample transfer.
  7. As soon as possible, take absorbance and fluorescence measurements.
    1. Use one of your filtered control samples as a blank.
      1.  You can use your blank to evaluate whether or not contamination has occurred during the extraction process.
  8. Acidify and dilute the sample with MilliQ water to 20 mL total volume and store for BEPOC and δ13C analysis.
    1. Make sure you record final volume of each sample! You will need to account for dilution when recording final BEPOC concentrations.

Sediment samples

  1. Prepare three (3) 0.1 N NaOH blanks as described above.
  2. Transfer approximately 1 mg OC (preferrably as wet/moist sediment) from homogenized sample into 15 mL centrifuge tube.
  3. Add 10 mL of 0.1 N NaOH to each sample. Vortex (or shake) for 1 minute to disaggregate particles and suspend in base solution.
  4. Refrigerate for 24 hours.
  5. After 24 hours, centrifuge samples.
    1. 2000-3000 rpm for 10 minutes.
    2. Decant the supernatant into clean tubes.
  6. Neutralize the base extract with concentrated HCl (do this in a fume hood).
    1. Add ~ 90 µL of HCl initially. If you over acidify, immediately add ~100-200 µL of 0.1 N NaOH, it should have a pH of ~ 6-7.
  7. Ensure final pH is ~7 (or near the pH from sample environment).
  8. Store samples at 4 °C in the dark until optical and OC analyses.

References

Brym, A., Paerl, H. W., Montgomery, M. T., Handsel, L. T., Ziervogel, K., & Osburn, C. L. (2014). Optical and chemical characterization of base-extracted particulate organic matter in coastal marine environments. Marine Chemistry, 162, 96-113.