Frequently Asked Questions
WARNING: We DO NOT ACCEPT samples with enriched 14C (often used as a tracer). Any contamination of any amount of enriched 14C ("hot") material may cause thousands of dollars in clean-up and other costs. If you submit "hot" samples to this lab, you may be liable.
- Plan for a normal turn around time of about 3 months. We always try to get samples done sooner if at all possible.
- Yes, you can pay via credit card (VISA or Mastercard)
- A purchase order (PO) number is required only if your institution demands it.
How to pack samples for shipping.
- Include a copy of the submission form inside the box with your samples (and the reference number of the job if possible). Reception at times removes outer labelling and we are left with nothing to ID the samples.
- DO NOT SHIP GLASS-ON-GLASS!!! Either wrap each vial or bottle individually with bubble wrap or other padding, or make sure there is a layer of cardboard between each (if less than 50 ml) and that the content is packed tightly (no movement within the box or boxes).
- Make sure that lids will not vibrate loose; wrap lids with tape or Parafilm.
- DO NOT USE ICE CUBES for samples that need to be kept cool (not even in baggies). They melt, make a mess, and can destroy labels. A courier may refuse to handle a leaking package, especially if there is a preservative added to the samples.
- Insulate the entire shipment in cold weather to prevent freezing and breakage of liquid samples.
- If you are sending samples in duplicate or triplicate, it is helpful for us for them to be grouped together.
- Solid samples must be dry and powdered.
- Make sure lids are air-tight for all vials or bottles.
- Filters may be wrapped in aluminum foil, or put into wide-mouth vials (eg scintillation vials).
How much material do I weigh for CN analysis?
Since the %C is almost always larger than the %N, it is usually the %N that determines the amount of material to weigh.
In general, the equation 10 ÷ %N will give you the mg of material to weigh, targeting 100µg of N.
If that amount is larger than about 200 mg, it would be better to use 5 ÷ %N. We can even do 3 ÷ %N if needed.
If you have groups of material with quite different C:N ratios, it is best to put them in different submission files. Contact us if you need help deciding.
You must always include the %N and %C data in the submission forms, as well as the weights. We need to know the C:N in order to determine the dilution setting to use for the 13C analysis.
When the C:N is about 50:1, up to about 75:1:
Please contact someone at the lab to verify the amount of material you should weigh. At this point, a compromise is needed. We reduce the normal target of 100µg of N in order to also reduce the extremely high amount of C.
When the C:N is about 75:1 or more:
At this point it is strongly recommended to run for 15N and 13C in separate runs. The compromise is too great to get good data in a single run.
When running for 15N, we will use a CO2 trap to prevent the large slug of CO2 generated in the EA from reaching the IRMS.
The rules above still apply to the weights needed for 15N.
When running for 13C only:
A target of 300µg of C is optimal. (i.e. 30 ÷ %C). The general rule above applies to C in this case as well. We can use less material if needed, please contact us.
How to prepare waters for dic/doc or tic/toc 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 are often several weeks delay.
- Number of replicate vials per sample:
Concentration only (ppm-C) = 1 vial 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 now advise that you put the darker PTFE side against the water. The rubber side of the septum can potentially affect the organic carbon. (A. Parkes, 2016, verbal communication).
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 organic and inorganic C concentrations of 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 handle extreme samples. Deep ground waters tend to be very problematic. If accepted, your high salinity and/or 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.
Why do I need to worry about carbonates in my sediments or soils?
- Analysis of sediments or soils analysed for carbon is a bulk method. The EA cannot distinguish between inorganic and organic carbon.
- Even a very small amount of carbonate-C can change the organic carbon 13C signature. See table below.
|Relative % inorganic C
where 13Cinorg @ -5‰
where 13Corg @ -25‰
|5%||-24.0‰||1.0‰||4.2||Ballpark; in a rush.|
|2.5%||-24.5‰||0.5‰||4.1||Definite small effect|
|Yes. Real value!|
What method should I use to remove carbonates from soils or sediments?
- There is no perfect method.
- First you need to determine the type(s) of carbonate(s) present in your soil or sediment. Calcite is easy to remove; dolomite is possible to remove with more work. Anything more durable is extremely difficult to remove.
- Do a literature search to see what method others in your field have used. Make your choice based on this information, and on the type(s) of carbonate(s) present.
- Make sure to retain some untreated material to use for N analysis if desired; any treatment of the sediment or soil can affect the nitrogen signature. We strongly recommend running the N and C isotopes separately for best results.