Abstract: A number of analytical challenges hinder the accurate identification and quantification of per and polyfluoroalkyl substances (PFAS) in the environment. These challenges include the lack of reference materials for PFAS as well as the ionization variability due to matrix interferences in electrospray ionization. In this externship, I plan on addressing these challenges by evaluating major matrix characteristics of environmental water samples and their relationship to the ionization efficiency. The observed relationships will be used to develop a preliminary statistical model for the semi-quantitation of PFAS without reference materials. Through collaboration with the United States Environmental Protection Agency, I will gain expertise from mentors, Dr. Sobus and Dr. McCord, in using cheminformatics for solving analytical problems. The semi-quantitation model developed as a result of the externship can be used to quantify transformation products of PFAS degradation studies, such as the nano bio-remediation techniques designed under the parent NIH grant, R01ES032717.