Sieg suggested we check out the UC Davis Isotope lab which nitrogen and carbon isotope sampling for pretty darn cheap ($8.50). Here’s the website and details: http://stableisotopefacility.ucdavis.edu/13cand15npricing.html.
In theory, we should be able to identify the source of the nitrogen (fertilizer versus from the air via soil biology). As a estimate of the biological activity of the soil, this is an effective and relatively inexpensive addition to our suite.
We would need to moderately grind, weigh, dry, and pack the sample before shipping so there is some minor prep work. It also takes about 10 weeks to get the result, so this will no provide immediate feedback!
I called the lab with some questions and here’s what I got back:
- How accurate does the weight need to be?
- depends on material
- if we need to calculate absolute %N and C of the sample, weighing down to .001g is suggested.
- However, if we’re just interested in the ratios of N isotopes and C isotopes, then we only need to get down to .1g. In our case, we’re really just interested in those ratios, not the absolute values.
- how mashed up does the sample need to be?
- again, depends…
- incomplete combustion isn’t the reason for grinding (that’s good), the reason to grind it is based on ensuring a representative sample, that’s all. In our case for plant material, that won’t require a ton of grinding - we just need to make sure the sample we’re submitting is representative of the object.
- Does it need any other prep work?
- Drying is important for shelf stability. You can freeze it, but you still need to dry to avoid mold growing. The water isn’t an issue from the standpoint of the test itself, it’s just bad because it can cause molding.
- For us, we could probably prep all samples, put them in the freezer, then once we have a full 96 well plate, dry them all together before shipping.
- What other factors do we need to know to reduce error?
- be care of nitrogen contamination (from nitrile gloves for example).
- avoid punctures in the capsule as powder and sample can come out.
- optimal sample weight should be ok. Doing dual C and N the calculator is good. Only N tends to overshoot