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What is an isotopically enriched spike in isotope dilution analysis?

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Figure 1: An electron bombardment ion source in cross section. An electron beam is drawn from the filament and accelerated across the region in which the ions are formed and toward the electron trap. An electric field produced by the repeller forces the ion beam from the source through the exit slit. — mass spectrometry Figure 1: *An electron bombardment ion source in cross section.* An electron beam is drawn from the filament and accelerated across the region in which the ions are formed and toward the electron trap. An electric field produced by the repeller forces the ion beam from the source through the exit slit.

In the context of mass spectrometry and isotope dilution, an isotopically enriched spike—often simply called a spike—is a small, precisely measured quantity of an artificially enriched isotope added to a sample.123

This spike is typically a highly purified form of a low-abundance natural isotope, though an ideal spike consists of an isotope with a mass that does not occur in nature at all, such as lead-205 produced in a cyclotron.2

By adding a known amount of this tracer to the original material and thoroughly mixing them, researchers can determine the quantity of an unknown element by measuring the resulting ratio of natural to enriched isotopes in the mass spectrometer. This technique is a powerful analytical tool because it allows for the measurement of invisibly small amounts of material and ensures that the loss of a portion of the sample during preparation does not affect the final result. Additionally, the use of these calibrated tracers facilitates the detection and assessment of contamination during the analytical process.123