CRIMS Applications

The CRIMS technique allows stable isotopes to be used in a wide variety of tagging and tracing applications. It is clear that stable isotopes may be substituted in most applications where radioactive species are currently used. There are, however a large number of new applications wherein isotopic labeling is now practical. In many of these the use of radioactive material is inappropriate because of safety or economic concerns. These disadvantages are eliminated with the use of stable isotopes. A good example is the study of drug metabolism in children. In this case it would be difficult to justify injecting radioactive species into a child but the use of stable isotopes does not present any problems. Other examples include: the analysis of material degradation and concentration, studies of transport systems, and the tagging of manufactured materials. Isotope labeling is most advantageous when the form of the final chemical to be detected is unknown (as in metabolism) or when the species to be tagged is normally difficult to identify, separate, or detect (as with an internal standard).

Material degradation and concentration involves either the breakdown of a compound or the concentration of a material via some man made or natural process. The degradation of DDT to DDE is an example in which both of these events occur. First DDT degrades in to the more toxic DDE. This compound is then concentrated in raptors via the food chain. In addition to the degradation of pharmaceuticals and pesticides, stable isotopes are currently under consideration for monitoring the decay of materials such as explosives and pollutants.

The study of transport systems covers a wide range of applications. These may range from the atmospheric distribution of pollutants to the under ground flow of fluids (i.e. water or oil). The petroleum industry has made wide use of tracers to further the understanding of oil and water flows in sub surface oil deposits. In some cases tracers have been used to monitor the activity of compounds in process streams (U.S. Patent 4,966,711, 10/30/1990). Even the study of building air circulation is a candidate for stable isotope tracers.

Manufactured products are often tagged to help identify their source. Examples, included explosives, pharmaceuticals, and petroleum products. The use of stable isotopes clearly has the advantage as taggents because they eliminate the need to add extra materials that can effect the function or performance of the product. Stable isotopes also make an ideal internal standard because they will behave in almost exactly the same way as an unlabeled chemical.

The academic and patent literature includes a wide range of examples in which materials other than stable isotopes are used as taggents or tracers. With the availability of the CRIMS analysis method, the extension of many of these works to include the use of stable isotopes is possible. We suggest that the use of stable isotopes should be considered anytime tagging or tracing is required. This consideration is a simple process for anyone familiar with a specific application. Some examples of applications where the use of stable isotopes and CRIMS may be appropriate are included in the above references. These are, however, only intended to serve as examples and do not include all possibilities.

A list of the elements currently used in CRIMS is shown below. However, any element with a stable isotope is a CRIMS candidate.

H, C, N, O, P, S, Cl, Se, Br.

Note that the term stable isotope may include radioactive species with a relatively long half-life.

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