Date of Award
Doctor of Philosophy
Dennis C. Johnson
Pulsed electrochemical detection (PED) previously has been shown to provide a sensitive and reproducible response for many aliphatic organic compounds separated by high performance liquid chromatography (HPLC). Herein, advancements in the application of HPLC-PED to amine compounds are demonstrated. Chromatographic methods are provided for the separation of alkanolamines, amines and diamines. Alkanolamines and amines are separated on a multimodal column that combines reverse-phase and cation-exchange retention behavior, and the chromatographic results are compared to results from a C18 reverse-phase column. Diamines are separated on a low-capacity cation-exchange column;Because the voltammetric response for alkanolamines, amines and diamines is dissimilar at Au, the PED waveform is optimized for each type of amine compound. Cyclic and pulsed voltammetry at a rotating disk electrode are used to determine the best detection potentials. Using the optimized PED waveforms, the detection limits are 5.0 pmol (200 nM) for diamines, 2.5 pmol (100 nM) for amines, and 500 fmol (20 nM) for alkanolamines separated by HPLC. The reproducibility of HPLC-PED response is very good, with relative standard deviation for multiple injections found to be better than 0.5% for both amines and alkanolamines;A novel application of PED also is introduced, in which PED is applied to the ring of a rotating ring-disk electrode (RRDE). The PED waveform makes the ring capable of continuously monitoring processes occurring at the disk, and the technique is applied to aliphatic amines, alkanolamines and the amino acid, glycine. A description of the each compound's potential-dependent adsorptive behavior is provided. The results for ethylamine indicate that it has two adsorption states on Au, with one type being reversible and facilitated by co-adsorption of hydroxide, and the other through irreversible adsorption directly to the reduced Au surface. The maximum surface coverage for ethylamine on Au is estimated to be less than one monolayer, with 75% being reversibly adsorbed. By optimizing the PED waveform to promote adsorption, the HPLC-PED response for aliphatic amines is improved significantly.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
David Allen Dobberpuhl
Dobberpuhl, David Allen, "Pulsed electrochemical detection for the investigation and determination of amine compounds separated by high performance liquid chromatography " (1994). Retrospective Theses and Dissertations. 10693.