BEPOM extraction
Last modified by Xwiki VePa on 2024/02/07 07:36
Step-by-step guides
Filter samples
- Prepare a 0.1 N NaOH solution (4 g NaOH + MilliQ in 1 L volumetric flask).
- Add 10 mL 0.1 N NaOH solution to each clean 15 ml centrifuge tube containing the POM filter.
- 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.
- Vortex/shake each centrifuge tube once the NaOH has been added.
- Important: make sure the POM filter is completely submerged after the tube has been shaken.
- Create 3 blank/control samples.
- Add NaOH to 3 cleaned centrifuge tubes that do not contain a filter.
- Put a batch of tubes in the refrigerator for 24 h.
- Add concentrated HCl to each bottle to adjust the pH=7 using 20-200 µL pipette.
- Add 0.1 N NaOH solution to neutralize if pH<7. Record both volumes added.
- 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.
- Filter the solution with a 0.2 µm filter and transfer to 25 mL polycarbonate bottles.
- Rinse these bottles with MQ or the NaOH solution prior to sample transfer.
- As soon as possible, take absorbance and fluorescence measurements.
- Use one of your filtered control samples as a blank.
- You can use your blank to evaluate whether or not contamination has occurred during the extraction process.
- Use one of your filtered control samples as a blank.
- Acidify and dilute the sample with MilliQ water to 20 mL total volume and store for BEPOC and δ13C analysis.
- Make sure you record final volume of each sample! You will need to account for dilution when recording final BEPOC concentrations.
Sediment samples
- Prepare three (3) 0.1 N NaOH blanks as described above.
- Transfer approximately 1 mg OC (preferrably as wet/moist sediment) from homogenized sample into 15 mL centrifuge tube.
- 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.
- Refrigerate for 24 hours.
- After 24 hours, centrifuge samples.
- 2000-3000 rpm for 10 minutes.
- Decant the supernatant into clean tubes.
- Neutralize the base extract with concentrated HCl (do this in a fume hood).
- 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.
- Ensure final pH is ~7 (or near the pH from sample environment).
- 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.