US 3788814 A
Description (OCR text may contain errors)
United States Patent US. Cl. 23-232 R Claims ABSTRACT OF THE DISCLOSURE Compounds multiply-labeled with stable isotopes and highly enriched in these isotopes are readily capable of detection in tracer experiments involving high dilutions. Thus, for example, 0 0 provides a useful tracer for following atmospheric pollution produced as a result of fossil fuel burning.
Background of the invention The invention described herein was made in the course of, or under, a contract with the Us. Atomic Energy Commission. It relates to a method of tracing labeled compounds at high dilutions and more particularly to the use of compounds multiply-labeled with stable isotopes as tracers.
The use of labeled compounds in the determination of various chemical and physical phenomena are well known in the art. Such compounds are usually described as tracers and until rather recently have generally been labeled with radioactive isotopes. The literature does disclose the use of tracers singly labeled with a particular stable isotope. 'Ihe isotopes most often used for this purpose are C, N, and 0. See, e.g., Myerson and Fields, Mass Spectrometry and Carbon-l3 Labeling, Science 166, 325-8 (Oct. 17, 1969). Heretofore, the use of stable isotopes for labeling has been severely limited by their scarcity and cost. However, the Los Alamos Scientific Laboratory, operated by the University of California for the US. Atomic Energy Commission, is now producing a substantial amount of C, N, and O which are available for purchase through the Atomic Energy Commission.
Tracer compounds for following the spread and distribution of atmospheric pollutants and contaminants are continually being sought. Radioactive tracers are known to be capable of performing this task. See, e.g., Nickola et al., Inert Gas Tracer System for Monitoring the Real-time History of a Dilfusing Plume or Puff, J. Ap. Meteorology 9, 621-6 (1970). However, radioactive tracers are now in ill repute as atmospheric contaminants themselves. Tracer methods using stable isotopes have been applied to atmospheric pollution studies. Dequasie and Grey, American Laboratory (Dec. 19, 1970), report the use of 8 0 and 0 0 for tracing the course of pollutants in the Salt Lake City area. Unfortunately, the variation in normal abundance of stable isotopes has customarily imposed a limitation on their use in tracer experiments involving high dilutions. The problem has been that compounds singly labeled with stable isotopes are exceedingly difficult to detect at high dilutions such as normally prevail in the atmosphere.
Summary of the invention We have now found that by using compounds with several labeled positions, this difiiculty may be avoided. Examples of such compounds are organic compounds completely substituted with C and carbon dioxide made Patented Jan. 29, 1974 of C and 0. Isotopes useful for this purpose are not limited to those given by example herein but may be selected from the class consisting of those stable isotopes having an abundance less than that of the most commonly occurring isotope of the element located at each labeled position of the compound. If the compound itself is normally rare, a combination of chemical separationsuch as by gas chromatography-with mass spectrometry permits detection with very large dilutions.
Although in the process of this invention, various multiply-labeled compounds may readily be used as atmospheric tracers, we have found that the triply-labeled 0 0 is particularly desirable for this purpose. The particular virtues of triply-labeled CO over other multiply-labeled compounds for atmospheric tracing are that (a) it is a normal minor constituent of the atmosphere and is thus a harmless additive; (b) CO is a chemical which is easily separated from the air for analysis isotopically; and (c) although it has been shown to be stable for several days, it then begins to exchange isotopically with water and is transformed to being singly labeled in the carbon atom only, while the oxygen atoms return to normal abundance. The natural disappearance of this triply-labeled form prevents a local region from becoming permanently saturated with the tracer and permits sensitive detection to be resumed after a few weeks at most. Triply-labeled CO may therefore readily be used for monitoring the spread and dissipation of the plume from fossil fuel smokestacks.
The method of this invention is not limited to atmospheric tracing but readily may be applied to any situation in which the labeled compound will be highly diluted. It is thus applicable to problems in hydrology, biology, and chemical process technology as well.
Concepts underlying the invention Some simple concepts of mixing as applied to isotopic mixing and dilution problems are formulated as follows:
A mixture of two substances A and B has a mol fraction C given by &
NA+N1B N (1) where N N and N denote mols of A, B, and total substance, respectively. A second mixture of composition C is similarly given by N CA N 2) Now let N mols of the first mixture be combined with N mols of the second. Its composition is C N+ CAN N +N (3) For isotope problems involving high dilution, regard C as being normal abundance. The difference C "-C is the deviation from this value. By Eq. 3
EXAMPLE 2 Use of depleted isotope, C =0, C =0.01, C -C "=10- Then MAL N or 1:1000 dilution.
EXAMPLE 3 Triply-labeled CO from C and O The normal abundance of this molecule in CO, is (0.01) (0.002) (0.002) =4 10-. Suppose that variations of 1:100 are detectable, so that C C =4 1O* Start with pure triply-labeled CO C '=1. Then dilutions of N'/N of 4 10- are measurable in pure CO In the atmosphere, however, where CO represents 3X10- it would be possible to detect 12x10- of this tracer. Thus a cubic kilometer of air at this concentration requires 0.1 STP liter of tracer for detection.
DESCRIPTION OF THE PREFERRED EMBODIMENT Experiments were preformed with triply-la-beled CO (Example 3) to determine its useful lifetime as a tracer in air. The carbon dioxide-49 was prepared from C0 by the following reactions:
Five milliliters of the carbon dioxide (77% mass 49) were injected into an air-tight box, 16 cubic meters in volume, containing normal air at the local pressure and temperature, 580 mm. Hg and C., respectively. The air within the box was stirred with a fan for a few minutes. Samples of the air (6 1.) were taken before and periodically after the addition of the labeled carbon dioxide gas, by expanding the air from the box into an evacuated container. All of the carbon dioxide was separated from the sample by flowing the gas first through a trap cooled to -80 to remove the water and then through a trap cooled to 190 to condense out the carbon dioxide. The latter trap was pumped on to remove all noncondensable gases and then the carbon dioxide was distilled into a sample holder for analysis in a mass spectrometer for the intensities of masses 44 through 49.
4 The initial and final ratios of masses 44-49 for each run are listed in the table. The useful life-time of the carbon dioxide-49 in air depends on the moisture content of the gas. Other experiments with mixtures of C O O and C O O in a mass spectrometer show that the oxygens exchange very slowly when the gas is dry. The half-life of the 00 -49 tracer could be as long as 1300 hours under conditions as severe as run 3 with the use of sensitive mass spectrometer techniques.
TABLE Related Half- Time humidity Mass-44! lite Run (hours) (percent) Mass-49 (hours) 0.15 as 7 98X10- 330 21.6 33 7 66X10- 0.05 6 61X10' 81 21.8 74 5 25X10' 0.05 s 16X10' 26 5 28. 1 95 4 01X10' What we claim is:
1. A method of tracing in atmospheric applications involving high dilutions of a compound which comprises multiply labeling said compound with highly enriched stable isotopes selected from the class consisting of those isotopes having an abundance less than that of the most commonly occurring isotope of the element located at each labeled position, and detecting said highly enriched multiply-labeled compound.
2. The method of claim 1 wherein a mixture of said highly enriched multiply-labeled compound with naturally occurring analogs is produced from a sample by chemical or physical means and said highly enriched multiplylabeled compound is detected within said mixture.
3. A method of tracking movements of air which comprises adding-to it carbon dioxide having carbon highly enriched in C and having oxygen highly enriched in O and detecting the enriched multiply-labeled carbon dioxide.
4. The method of claim 3 wherein said multiply-labeled carbon dioxide is triply-labeled C 0 References Cited Kamen, Radioactive Tracers in Biology, Academic Chem. Abst., vol. 75, p. 393, No. 82326W (1971).
MORRIS O. WOLK, Primary Examiner T. W. HAGAN, Assistant Examiner U.S. Cl. X.R. 25Q303