TITLE: Collecting samples for Dissolved Organic Carbon (DOC) analysis
AUTHORS: Krista  Longnecker

[DESCRIPTION]
This protocol describes collecting samples for Dissolved Organic Carbon (DOC) analysis. Dissolved organic carbon is operationally defined as the material that passes through a filter with a known pore size. Part numbers are in the materials section for GF/F filters (nominally 0.7 um) and PTFE Omnipore filters (we use 0.2 um for this protocol, many sizes are available).

This protocol assumes you are using Niskin bottles to sample water at a desired depth.


[STEPS]
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
1. The glass vials need to be combusted before use. 
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
1.1. Set aside the caps that were sent with the vials because they cannot be combusted.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
1.2. Wrap packs of glass vials in foil prior to combusting them.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
1.3. Combust the glass vials at 450 °C for at least 240 min.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
2. If you are using GF/F filters, they also need to be combusted before use. It is easiest to combust them in batches of ~25 in foil-wrapped glass petri dishes.

Omnipore filters cannot be combusted and are used as is from the package.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
3. Use electrical tape or lab tape to label the glass vials. Do not use too much tape as that causes problems with inserting the vials into the autosampler. We prefer 1/2 inch label tape, placed towards the top of the vial. Be sure to wrap the tape all the way around the vial in order to prevent the labels from falling off during sample processing.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
4. In the field, use gloves for all sampling.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
5. Place one filter (GF/F or Omnipore) into the polycarbonate filter holder. Make sure the filter is centered in the holder before tightening the two halves of the filter holder.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
6. Attach the filter holder to the Niskin using the silicone tubing.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
7. Open the top valve on the Niskin and press in the sampling nipple to begin the flow of water.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
8. As needed, vent air out of the filter holder using the valve on the top of the filter holder.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
9. Rinse the 40 ml glass vials 3x with sample water.
SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
10. After rinsing, fill each vial up to the shoulder with the sample (40 mL).

SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
11. Add 40 µL of 12 M hydrochloric acid to this vial.

SECTION: Collecting samples for Total Organic Carbon (TOC) analysis
12. Store the acidified samples at 4 °C in racks/boxes that keep vials from knocking into each other.