SDSU Thesis Defense - 2008 Spring - Jennifer Piper

Column Matrix Effects in the Mass Spectrometer and the Effects on Isotope Analyses Jennifer Piper B.S. Candidate Department of Geological Sciences San Diego State University Advisor Dr. Aaron Pietruszka Mass spectrometry can be used to analyze radiogenic and stable isotopes in order to determine the concentrations of different isotopes in a sample, ages of rocks, and sample correlations. Multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has become the preferred method for isotope analysis compared to other methods because it is very precise, the plasma can ionize any element, and there is less time required for each analysis. One of the downfalls of isotope analysis using MC-ICP-MS is that it induces an instrumental mass-dependent fractionation (instrumental mass bias) that needs to be corrected for. This instrumental mass bias is primarily due to the extremely high temperatures of the plasma, which causes a spread in ion energy during ionization and transport within the mass spectrometer. Instrumental mass bias in the MC-ICP-MS can be corrected using one of two main techniques (1) standard sample bracketing (SSB) or (2) double spiking. SSB is commonly favored, but it is more susceptible to matrix effects that result in inaccurate results. Many different types of matrix effects in the MC-ICP-MS have been identified and corrected for. Spectral matrix effects, or isobaric interferences, result from the occurrence of an element that overlaps in mass with the isotope of interest. Non-spectral matrix effects can create differences in the measured isotope ratios of a sample and the standard. In a recent study, a new and possibly uncontrollable matrix effect was found that is thought to have come from the separation and purification of molybdenum using an anion exchange resin. It was shown that the collection of a pure Mo-free solution that had been passed through an anion exchange resin and subsequently added to a Mo standard appeared to be isotopically lighter than expected when compared to the same untreated Mo standard. http://www.geology.sdsu.edu/people/students/theses/spring2008/jennifer_piper.html

Google Video | May 12, 2008