Isotopic tracers

Radioisotopes are used in many settings to trace the flow of materials. Usually this is accomplished with an isotope with a short half life to avoid long term contamination. With the advent of gas chromatography--mass spectrometry, stable isotopes are increasingly being used for the same type of studies. Isotopic tracers, both stable and radioactive, are currently being used in hundreds of studies. Some typical examples are:

• field studies of soil nutrient and water movement,
• determination of carbon fixation pathway,
• plant water use efficiency and nitrogen utilization,
• measurements of metabolism and nutrient uptake,
• determination of climatically relevant heat exchanges between the atmosphere and oceans, and
• water current studies in oceans.

Isotope dilution is frequently used to assess the amount of non-radioactive materials in a sample. Isotope dilution is a quantitative analysis rather than a qualitative analysis. In an isotope dilution, a radioactive compound is released into an unknown mixture. After allowing time for mixing and even distribution, a sample is collected and counted. After correction for the half-time, the size of the initial mixture can be estimated by the calculating the amount of dilution of the isotope.

Many universities, including Texas [local] and Hawaii [local], support isotope dilution laboratories