Spectrophotometric Determination of Hydroxycinnamic Acids in Herbal Drugs. Part 2. Determination of Hydroxycinnamic Acids in the Presence of Polyphenolic Compounds (Review)

Abstract

INTRODUCTION. Polyphenolic compounds of various classes have pronounced absorption bands overlapping in almost the same ultraviolet region. This superposition of bands complicates the quantification of total hydroxycinnamic acids in herbal drugs by direct spectrophotometry without additional sample preparation.AIM. This study aimed to establish the possibility of quantifying hydroxycinnamic acids in herbal drugs by spectrophotometry in the presence of other polyphenolic compounds.DISCUSSION. This review analyses publications on analytical procedures for the spectrophotometric quantification of hydroxycinnamic acids that are based on the preliminary separation or chemical modification of polyphenolic compounds (combining the use of spectrophotometry, chromatography, extraction, Arnow’s reagent, etc.). The described sample preparation can help to resolve absorption bands in the spectra of polyphenolic compounds. The results of assessing the characteristic parameters of these analytical procedures (selectivity, sensitivity, labour intensity, etc.) can serve as a basis for searching novel approaches to the quantitative determination of hydroxycinnamic acids in plants.CONCLUSIONS. To determine the content of hydroxycinnamic acids in mixtures of polyphenolic compounds, analysts may use special sample preparation (combining spectrophotometry with chromatography and extraction) or chemical modification of the initial compounds. The acquired spectra could benefit from specific mathematical processing (derivative photometry and Vierordt’s method). However, even with the abovementioned approaches, it may not always be possible to increase the selectivity of an analytical procedure. Therefore, there is a need to further improve existing analytical procedures for the quantification of hydroxycinnamic acids and develop new ones.

Keywords

• hydroxycinnamic acids
• phenolcarboxylic acids
• caffeic acid
• cinnamic acid
• chlorogenic acid
• chicoric acid
• herbal drugs
• quantitative determination
• spectrophotometry
• chromatography–spectrometry
• extraction spectrophotometry
• arnow’s reagent
• differential spectrophotometry
• polyphenolic compounds