USGS logo

You are what you eat

Results | Food Web and its Function | Interesting Isotopic Studies

Food Web and its Function

How is your fingernail sample prepared and analyzed?

  1. About 1 milligram of your fingernail clippings will be put into a tiny tin foil capule, which will then be crushed closed.
  2. The tin capsules are loaded into an automated sampler which will drop the samples, one by one, in to a furnace heated to 1100 C where the sample is instantly combusted to CO2, N2, H2O, and other gases.
  3. A flow of helium then carries the gases through scrubbers that remove unwanted gases, and a gas chromatograph column that separates the remaining CO2 and N2 gases so that they can be separately analyzed (Figure 2).
  4. The gases then flow into the mass spectrometer where the isotope ratios of CO2 (13C/12C) and N2 (15N/14N) are measured.
  5. A computer controls the mass spectrometer, collects the data, and calculates the isotope ratios from the small voltages measured.
Fig. 2. Understanding how a mass spectrometer works. View larger image
Spectrometer
What is a food web?
Why study food webs?
Using carbon and nitrogen isotopes
Analyzing fingernails
Results | Food Web and its Function | Interesting Isotopic Studies

Please contact Carol Kendall (ckendall@usgs.gov) for questions and comments regarding this page.
This page was last changed in June 2003.
To the USGS Home Page
To the Water Resources Information Home Page