HPLC With Electrochemical and Photodiode Array Detection Analysis of Tocopherol Oxidation and Nitration Products in Human Plasma

Advances in analytical methodologies in the isolation, characterization, and quantitation of lipid-soluble antioxidants, such as vitamin E, have evolved since its discovery in 1922 (
1
). The primary purpose of vitamin E (tocopherol) and its tocopherol homologs is to act as free radical scavengers to control lipid oxidation in the body (
2
). The physiological and biochemical processes lipid-soluble vitamins possess are beneficial in preventing a number of degenerative diseases and conditions such as Alzheimer’s disease and Parkinson’s disease (
3
–
7
), cardiovascular disease (
8
–
10
), and cancer (
11
–
13
). Pharmaceutical, medical, as well as industrial disciplines have been interested in the clinical outcomes of tocopherol studies. Thus, a critical need exists to measure multiple tocopherols and their oxidation products simultaneously in human tissue (
2
,
14
–
19
). Our laboratory is interested in studying lipid nitration products in biological matrices primarily as biomarkers to determine the level of oxidative stress and tissue damage. 3-Nitrotyrosine has been determined to be a useful protein biomarker employed to measure oxidative stress based in previous publications (
20
–
26
). The most commonly measured nitrated tocopherol compound of interest is 5-NO
2
-γ-tocopherol (
2
,
19
,
27
,
28
). This and other tocopherol congeners of interest are depicted in Fig. 1 . High performance liquid chromatography (HPLC) with combined electrochemical and photodiode array detection (HPLC-ECD-PDA) is a relatively new, versatile and reliable chromatographic technique employed to generate high sensitivity and selectivity, reproducibility, and accuracy in the determination of tocopherol homologs.Fig. 1.
The chemical structures of the different tocopherol congeners discussed in the text.