HPLC-MS : Chapter Eight

Chapter eight

Analysis of Carotenoids Using Atmospheric Pressure

Chemical Ionization Mass Spectrometry

Natasa Pajkovic and Richard B. van Breemen

Department of Medicinal Chemistry and Pharmacognosy, University of Illinois College of

Pharmacy, Chicago, IL 60612

Introduction

Carotenoids are naturally occurring pigments found in a wide variety of plants, algae and several lower organisms (1), and more than 600 naturally occurring carotenoids have been isolated and characterized (2). Due to an extensive conjugated polyene chain, carotenoids typically are bright yellow, orange, red, or purple with absorption maxima in the range of 400–500 nm (3). These polyisoprenoid compounds are synthesized by plants and .microorganisms and interact with chlorophyll during photosynthesis to absorb light and transfer energy (4–6). Another result of their conjugated polyene chain is the ability of carotenoids to quench singlet oxygen and free radicals and thereby protect plants from photooxidative damage (5,6). Carotenoids have been classified into two groups, hydrocarbon carotenes and oxygenated xanthophylls (7), and the structures of carotenes and xanthophylls that are common in the human diet are shown in Figure 8.1.

In addition to their protective functions in plants, diverse biological functions in humans have been attributed to carotenoids (8,9). Approximately 50 carotenoids are precursors of vitamin A, which is essential for vision, cellular differentiation, and embryological development (10). It has been suggested that carotenoids can function in humans as antioxidants and immunoenhancers (11), as well as prevent age-related macular degeneration (12), cancer (13), and cardiovascular disease (14). Because of these clinical effects, the importance of the detection and identification of carotenoids in natural sources, biological tissues, and clinical samples has been increasing during the last 10 years.

Because of their extended system of conjugated double bonds, carotenoids are usually unstable in the presence of light, heat, or oxygen (7). Therefore, the isolation, identification, and quantitation of these pigments can be challenging (15). Complex biological samples such as human serum, tissues, and plant material often contain compounds than can interfere with the isolation of carotenoids or mixtures of carotenoids with similar structures.