I． Definition of Isotopes

1．Isotope: nuclides with the same atomic number but differing in mass number.

2．Stable isotope:elements with the same proton number but different neutron numbers, and free ofradioactivity.

3．Labeled compound: acompound which is recognizable and can be used as a tracer by means of substituting radioactive and stable nuclides for one or several atoms of themolecule of compound.

4．Tracer: substance with certain distinct features and easy-to-recognize qualities. As long as asmall amount of it is mixed with or attached to another substance, the distribution and the location of the sample can be determined.

5．Abundance: the atomic(or molar) ratio between stable isotope and the element.

6．Natural abundance:natural existent abundance of a specific isotope in an element

7．Isotopic tracer: atracer which is the same with the traced element, but differs in atomic structure and energy state.

8.   Isotope dilution analysis: an analytical method for figuring out the content ofan element in the sample (or the substance) by means of adding to the sample acertain amount of the element’s isotope whose abundance is known (or asubstance containing the isotope), and testing its abundances in the sample both before and after the mixture.

9.   Isotope effect: physical and chemical differences of the atoms and molecules of an element’s isotopes due to differences in nuclei properties such mass andspin, etc.

10. Atomic mass: a neutral atom’s rest mass when it is in ground state.

11．u，atomic mass unit: one twelfth of a neutral ¹²C atom’s rest mass when it is in groundstate. 1u=1.6605655×10^-27kg。

12.L，NA:molecule number divided by substance mass. NA=N/n= (6.022045±0.000031) ×10 ²³mol-1。

13.M: mass divided by amount of substance. M=m/n，in which “m” refers to amount of substance, kg/mol。

14.Mole: amount of substance of a system, whose basic unit number is the same as0.012kg¹²C’s atomic number. Mole’s basic unit, which should bespecified clearly when mole is in use, can be atom, molecule, ion, and otherparticles, or specific combinations of these particles.

II  Introduction of StableIsotope

 So far, 274  types of stable isotopes have been found, butwith only a few of them such as²H、¹³C、¹⁵N、¹⁸O、²²Ne、¹⁰B inindustrialized production and widely application. Stable isotopes’ massdifferences contribute to the great differences in terms of nuclear spinproperty, and relative frequency and sensitivity of nuclear magnetic resonanceas well, which provide a technical basis for methods of testing stableisotope’s abundance such as mass spectrometry and nuclear magnetic resonancemethod, etc.

Stable isotopes as well as their compounds possess the samechemical and biological properties, and differ in nothing but their nuclearphysical property. Therefore, they can be used as tracing atoms, and made intolabeled compounds with stable isotopes. Based on their different propertiesfrom those of corresponding unlabeled elements, stable isotopes’ after reactivelocation, total amount and reactive amount can be tested through analyticalinstruments such as mass spectrometer and nuclear magnetic instrument, etc. Asa result we can know the theory, process and effect concerning the reaction.

Due to the fact that stable isotopes are free fromradioactivity, no special protection methods are required in processes such asseparation, synthesis of labeled compounds or application. Stable isotopes enjoysuch features as simple operation, safety in use and no radioactivity, and canbe directly applied to animals and human beings in terms of nutriology,clinical medical research and metical diagnosis, etc.