SPEX CertiPrep Claritas PPT® Isotope Standards can be used for isotope dilution analysis and internal standards. The internal standard element must have similar characteristics to the tested/measured element(s) and not be present in the sample. Using isotope modification standards, the chemist can use less internal standard and have a higher intensity reading while avoiding interferences. Every Claritas PPT® Standard is supplied with a comprehensive SPEXertificate®.