Atoms of the same element (i.e. having the same atomic number) which differ in mass number are called isotopes of that element. The isotopes of an element are identical in chemical properties, and in all physical properties except those determined by the mass of the atom. The different isotopes of an element contain different numbers of neutrons in their nuclei. Nearly all elements found in nature are mixtures of several isotopes.

(Uvarov, E. B., d. R. Chapman, and A. Isaacs. A Dictionary of Science. Third Edition. Penguin Books Ltd., Harmondsworth, England, 1966.)

The term "isotope" was found in the following pages:

SCIX 2012 (FACSS 2012): The Great Scientific Exchange | EVISA's Agenda of Events
Instrument database: Innov-X Systems - Innov-X Inspector Series™
Chlorine speciation analysis in complex hydrocarbons using GC-ICP-MS/MS | EVISA's News
Tin and mercury content and speciation in red wine from different countries | EVISA's News
24. ICP-MS Anwendertreffen und 11. Symposium Massenspektrometrische Verfahren Elementspurenanalyse 2014 | EVISA's Agenda of Events
Instrument database: New Wave Research, Inc. - UP213 deep-UV YAG Laser Ablation System
Chromium speciation in solid matrices | EVISA's News
Liquid-liquid extraction in speciation analysis | EVISA's News
Instrument database: CETAC Technologies - GeoLasPro 193nm Excimer Laser Ablation System
Company database: Icon Services
Material database: American Elements - Zirconium 91 Oxide Isotope
Link database: Mineral Information Institute: Thorium
Material database: American Elements - Tungsten 183 Metal Isotope
Material database: American Elements - Copper 65 Oxide Isotope
ICMGP 2015: 12th International Conference on Mercury as a Global Pollutant | EVISA's Agenda of Events
Material database: American Elements - Lithium 7 Metal Isotope
Books and Special Issues on Elemental Speciation (published between 2016 and 2020) | EVISA's News
Instrument database: Elemental Scientific Inc. (ESI) - PC3-SSI Peltier cooled Spraychamber
EVISA Workshop on: Mercury speciation analysis - The basis for sound risk assessment, and optimized remediation strategies for contaminated soils, sediments and sludge | EVISA's Agenda of Events
Experts in Bioimaging came together in Münster, May 24-25, 2018 | EVISA's News