[4] She has been recognized as an outstanding scientist in the field of bioanalytical chemistry because of her work using mass spectrometry to study biomolecules.

Djerassi's lab examined electron ionization of molecules, studying basic mechanisms such as fragmentation and hydrogen transfer.

For her thesis research, Catherine made a series of deuterium labeled analogues of amines, alcohols, esters and amides.

They were successful in obtaining funding from the National Science Foundation for a CEC 21-110 double-focusing mass spectrometer for Fenselau to use.

[1][8] Although Fenselau and her second husband Robert Cotter both worked in mass spectrometry at Johns Hopkins, they chose to develop independent careers rather than a joint lab.

"[6] In 1987, Catherine Fenselau moved to the University of Maryland, Baltimore County (UMBC) to become chairperson of the Department of Chemistry and Biochemistry.

Research areas studied in the lab included biopolymer structure, ion thermochemistry, proton-binding entropies, glucuronide and glutathione conjugation, and possible mechanisms for acquired drug resistance.

The Fourier transform mass spectrometer used a strong magnetic field to trap and excite ions and measure the resulting electrical signals.

Appointed Chairperson of the Department of Chemistry at University of Maryland, College Park in 1998, Fenselau supervised the disassembly, transport, and reassembly of the complex instrument, moving it safely to her new lab.