Radioisotope methods

The use of radiotracers is dependent on certain basic assumptions being fulfilled. The first assumption, mentioned above, is that the radioactive isotopes of a given element behave identically as the stable isotopes of the same element. Actually, this assumption is not exactly true. The difference in masses between radiotracer nuclei and stable nuclei can cause a shift in the reaction rate or equilibria (the isotope effect). It is true, however, that in most cases the isotope effect does not significantly affect the utility of the radioisotope method. Since the degree of chemical bond stability due to vibrational motion is directly related to the square root of the masses of the isotopes involved, it is apparent that an isotope effect will be of significance only for elements of low atomic weight (at wt <25). 

Sokoloff L, Smith CB (1983) Basic principles underlying radioisotopic methods for assay of biochemical processes in vivo. In Greitz T, Ingvar DH, Widen L, eds. The Metabolism of the Human Brain Studied with Positron Emission Tomography. New York, USA Raven Press pp. 123-148. 

The number of disadvantages outweigh the advantages of radioimmunoassays and this leads to development of non-radioisotopic immunoassay methods. Many substances can be firmly attached to the antibody without changes in binding properties towards the antigen. This principle has been used in some methods to be competitive with radioisotopic methods. In order for alternate methods to function as alternatives to radioisotopic... 

Treatise on Analytical Chemistry, Part I Theory and Practice, 2nd ed., Vol. 14 (Eds. Ph. J. Elving, V. Krivan, I. M. Kolthoff), Section K, Nuclear Activation and Radioisotopic Methods of Analysis, Wiley, New York, 1986. 

Esters, Ethers, and Related Derivatives of Alcohols.— The long-recognized differences in reactivity of the 3a-, 7a-, and 12a-hydroxy-groups in cholic acid to acetylation (3a > 7a > 12a) have been attributed to conformational and steric effects [3a-equatorial 7a- and 12a-axial, and seemingly differentiated by greater steric hindrance at C(12), due to the side-chain]. A new investigation, however, shows that the reactivities of the monohydroxycholanic acids are in ratio 3a 7a 12a 97 1.0 1.5. ° A novel radioisotope method was used for... 

Serum folate concentrations should not be measured by the radioisotope method in patients taking trimethoprim (202). 

Insulin autoantibodies (lAAs) are present in more than 90% of children who develop type 1 diabetes before age 5, but in fewer than 40% of individuals developing dia-betes after age 12. Their frequency in healthy people is similar to tliat of ICA. A radioisotopic method that calculates the displaceable insulin radiohgand binding after the addition of excess nonradiolabeled insulin is recommended for lAA. Results are positive when concentrations exceed the mean +2 (or 3) standard deviations (SD) of healthy controls. An important caveat is that insulin antibodies develop after insrdin therapy, even in those persons who use human insulin. 

NAA and radioisotopic methods are less frequently applied to Ag than to Au determination. An example for the application of ultraclean laboratory techniques is described for the determination of silver and other chalcophile elements in Antarctic ice, by isotope... 

Dominik A, Mangini A, Muller M (1981) Determination of recent deposition rates in Lake Constance with radioisotopic methods. Sedimentol 28, 653-677. 

Vadas MA, Miller JFAP, Gamble J, Whitelaw A. A radioisotopic method to measure delayed-type hypersensitivity in the mouse. I. Studies in sensitized and normal mice. Int Arch Allergy Appl Immunol 1975 49 670-692. 

The decay rate (activity) of a sample is proportional to the number of radioactive nuclei. Nuclear decay is a first-order process, so the half-life does not depend on the number of nuclei. Radioisotopic methods, such as C dating, determine the ages of objects by measuring the ratio of specific isotopes in the sample. 

Excellent, comprehensive treatments of the principles and fundamentals of nuclear activation analysis - including applications fundamentals - are found in the following five consecutive chapters in the first edition of Treatise on Analytical Chemistry Finston (1971a) (Radioactive and isotopic methods of analysis nature, scope, limitations, and interrelations) Finston (1971b) (Nuclear radiations characteristics and detection) Crouthamel and Heinrich (1971) (Radiochemical separations) Seaman (1971) (Tracer techniques) and Guinn (1971) (Activation analysis). A series of seven similarly comprehensive chapters appeared in the updated second edition Lieser (1986), (Fundamentals of nuclear activation and radioisotopic methods of analysis) Herpers... 

Bowen HJM (1986) Introduction to radiotracer experiments. In Hiving PJ, Krivan V and Kolthoff IM, eds. Treatise on analytical chemistry, Part 1 (Theory and practice). Second edition. Vol 14, section K (Nuclear activation and radioisotopic methods of analysis), pp. 193-239. John Wiley Sons, New York. 

---