Isotope Dilution Mass Spectrometry

Isotope dilution mass spectrometry (IDMS) is an analytical technique based on the modification of the natural isotope composition of elements or compounds after the addition to the sample of an enriched isotope or an isotopically labeled form of the analyte. The isotope composition in the mixture, measured by Mass Spectrometry, provides the concentration of the analyte in the sample after simple calculations. IDMS has been regarded as a highly qualified primary method capable of providing accurate and precise results directly traceable to the International System of units. Additionally, IDMS is an essential tool in many research laboratories for the validation of analytical methods of lower metrological quality and for the certification of reference materials. In the last few years, many IDMS applications are being implemented in routine testing laboratories as the reduction of total analysis time and the increase in analytical quality provided by IDMS pays off the cost of the acquisition of isotopically enriched/labeled material. This chapter details basic theoretical and practical considerations required to successfully apply IDMS for the determination of elements and compounds. Special attention has been paid to explain the main factors affecting the accuracy and precision of the measurement of elemental and molecular isotopic compositions.