How to prepare water samples for inorganic/organic carbon analysis
- We require the use of 40mL pre-cleaned borosilicate EPA vials with septa caps, purchased from a major laboratory supplier; quality assurance grade is not necessary. Please order your EPA vials early; there is often several weeks delay.
- Number of replicate vials per sample:
Concentration only (ppm-C) = 1vial per sample
Inorganic 13C (DIC/TIC) only,with or without concentration = 2 identical full vials (no headspace) with extra septum
Organic 13C (DOC/TOC) only, with or without concentration = 2 identical vials (extra septum not necessary; a small amount of head space is ok)
Inorganic AND organic 13C (DIC/TIC & DOC/TOC) with or without concentration = 3 identical full vials all with the extra septum
- Extra septum:
Samples for DIC or TIC require an extra septum (PTFE-rubber, see info below) inserted between the top of the vial and the cap. The silcone/teflon septum provided with the EPA vials allow inorganic carbon to diffuse out unless the extra septum is used. The extra septum is not required for DOC or TOC; however if inorganic and organic carbon are required, please submit three identical full vials with extra septum (if re-running for DIC/TIC we must use a fresh vial). We used to recommend that the lighter coloured side of the extra septum (rubber) face the water, but it has recently come to our attention that the rubber might add a slight organic C contamination to the sample (A. Parkes, 2016, verbal communication). We now advise that you put the darker PTFE side against the water, unless submitting strictly for inorganic C. The lighter side of the septum can potentially affect the organic carbon.
PTFE-rubber, 22mm flexseal disc
In addition to your personal label on the vial, please label each sample cap from 1 to xx in the same order as each one is listed in the submission file. This helps us to quickly locate samples. Replicate vials should have the same number on the cap (i.e. the three replicate vials for the first sample in the sub file should all have "1" on the cap, etc.). Only enter this sample once in the submission file. Please include the number of replicate vials per sample that you are sending directly in the submission file.
Samples for DIC or DOC should be carefully and gently filtered to 0.45 um or less. Samples for TIC or TOC should NOT be filtered.
- Range of measurement:
We can analyse water samples ranging from about 0.5 to 100 ppm of carbon. The peripheral allows us to select a variable volume of sample according to the expected concentration (hence the importance of providing all pertinent concentration info). Please note: organic C and inorganic C concentrations can be vastly different. We must regularly re-run samples with varying volumes to target each one.
- Preservation agents:
Samples should remain refrigerated after sampling and kept cool but not frozen during shipping. We will transfer the vials to our refrigerator upon arrival. If the samples are refrigerated and analysed quickly it is preferable to not poison the waters for preservation. We do understand that in some cases it is necessary. If the waters are poisoned, it MUST be clearly stated in the submission file; include the type of poison as well.
- "Abnormal" water samples
"Normal" freshwater lake or river samples have ppm-C organic and inorganicwith less than 100 ppm. If your samples are out of the ordinary in any way (i.e. very high C concentrations, high salinity, organic contamination, very high or low pH, etc.), please contact us. We will let you know if we can analyse them. Our instrumentation is not adapted to extreme samples. If accepted, your high concentration samples can be diluted with deionised water for an extra charge. If your sample concentrations are below our minimum (0.5 ppm) there is nothing to be done; no isotopic data will be possible.
- Submission files:
- Only 1 media code per submission file.
- List each sample only once. Include the number of replicate vials per sample in the Comments column.
- List the type of water for each sample (e.g. lake, river, pond, sea water, ground water, etc.).
- Include the pH & salinity data for each sample if you have it; otherwise, give an estimate.
- Include the ppm-C (or mg/L) concentrations for the DIC and DOC of each sample if you have it; otherwise, give an estimate (helps enormously in estimating sample volume to use in analysis).
- If a preservation agent is used, include the type of agent and amount used in the general comments box.