Both d15N and d13C can be analysed simultaneously if the sample can meet certain criteria. In order to achieve accurate results it is necessary to work within the linear response range of our isotope ratio mass spectrometers (IRMS). This necessitates having an absolute weight of 20 to 200 micrograms of nitrogen and 40 to 800 micrograms of carbon in a single weighed sample. If you know the elemental composition and the %C:%N ratio is less than 40 then it should be possible to weigh a sample within range. If this cannot be achieved then it is our practice to run nitrogen and carbon isotope analysis as two separate analysis runs.
Precision (as average standard deviation) on well prepared samples will generally be better than 0.3‰ for nitrogen and 0.2‰ for carbon. We report nitrogen results referenced to air and carbon to Vienna Pee Dee Belemnite (VPDB) and if required the %N and %C obtained from our total beam values.
Although we prefer to weigh your samples we are able to accept pre-weighed encapsulated samples for this service. We monitor our IRMS total beam values to ensure that the weight criteria is met and will inform you if there are any discrepancies.
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