A method for internal standardization of cool plasma ICP-MS using one or more enriched stable isotopes includes introducing an enriched stable isotope of a chemical species to a sample containing a non-enriched isotope of the chemical species to form a sample and standard mixture. In implementations, the enriched stable isotope is introduced via an inline syringe addition to a flow of a sample solution containing a non-enriched isotope of the chemical species to be analyzed. The method also includes introducing the sample and standard mixture to an ICP-MS under cool plasma conditions. The method also includes determining an ionization amount of the enriched stable isotope by the ICP-MS. The method further includes correlating an ionization amount of the non-enriched isotope based on the determined ionization amount of the enriched stable isotope.