The role of liquid chromatography-mass spectrometry in the analysis of caffeic acid

Phenolic acids, one of the major classes of polyphenols, are widely distributed in the human diet, particularly in fruit, vegetables and beverages. Caffeic acid is a phenolic acid naturally occurring in many plant foods such as carrots, cabbage, tomatoes and several berries. It is also present in multiple beverages such as coffee, fruit juices and wine. Moreover, caffeic acid is one of the major active components in many traditional Chinese medicines. As a natural product, it possesses several biological and physiological activities. These activities include antioxidant, anti-mutagenic, anti-tumor and antiobesity effects. For these reasons, caffeic acid is also being developed into drug for sale, for instance for its use in the development of asthmatic and allergenic drugs. Although caffeic acid as well as other polyphenols are not essential nutrients, they are secondary metabolites synthesized by plants with bioactive properties, also known as phytochemicals, that may have an important effect on human health. For this reason, the interest in the analysis of this kind of compounds for the characterization of plant extracts is raising in the last years. Liquid chromatography coupled to mass spectrometry or to tandem mass spectrometry (LC-MS(/MS)) is one of the most frequently used techniques for that purpose, and the number of LC-MS(/MS) methods published in the literature dealing with the analysis of polyphenols, including caffeic acid, not only for their quantitative determination in food products and beverages but also for the characterization of foodstuffs and pharmaceutical preparations as a way to guarantee authentication regarding the natural product of origin is increasing. Additionally, LC- MS(/MS) techniques has also been used for the analysis of caffeic acid and its active metabolites in biological fluids to carry out pharmacological studies. Recently, high resolution mass spectrometry (HRMS) is acquiring also an important role in the analysis of caffeic acid, and polyphenols in general, and today several LCHRMS methods either using time-of-flight (TOF) or Orbitrap mass analyzers are described for the quantitative determination of these compounds as well as a fingerprint analysis for characterization, for instance in the case of herbal medicines. In this chapter the role of liquid chromatography-mass spectrometry in the analysis of caffeic acid will be discussed. LC-MS(/MS) chromatographic conditions, ionization sources, and MS and HRMS analyzers frequently used, as well as strategies for the structural characterization and the qualitative and quantitative analysis of caffeic acid, its active metabolites, and other phytochemicals will be discussed by means of relevant applications. Coverage of all kind of applications is beyond the scope of the present contribution, so we will focus on the most relevant applications published in the last years. \ua9 2015 by Nova Science Publishers, Inc. All rights reserved