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Introduction: Phenolic compounds are ubiquitous compounds found in all plants as their secondary metabolites. Phenols are becoming increasingly important particularly because of their beneficial effects on health., Objective: To provide a faithful calibration model for the simultaneous determination and quantification of phenolic acids, as salicylic, vanillic, p-hydroxybenzoic acids, eugenol and thymol in different extracts of medicinal plants, a comparative study was made between two methods of infrared measurements based on attenuated total reflectance (ATR) and transmission., Methods: Characteristic absorbance peak heights of mid-infrared spectra of individual phenolic acids were measured for the compounds. For partial least squares regression (PLS-R) calibration mixtures of phenolic acids, wavenumber ranges, spectra pretreatment and number of latent variables, were assayed to improve the prediction capability of models using different spectral preprocessing techniques after mean centring of infrared data. Plant extracts were prepared by using water/methanol and ethanolic extraction solvents followed by Fourier-transform infrared (FTIR)-spectrometry analysis. The concentrations of phenolic compounds contained in the extracts were obtained by using the best models selected of the PLS calibration., Results: PLS-ATR-mid-infrared (MIR) measurement provided the most accurate results and offers a good methodology for the determination of phenolic acids. The analysis showed that the rate of phenolic acids and monoterpenic phenols in extracts of medicinal plants is in the same range obtained with the Folin-Ciocalteu method, which confirm that the developed method using PLS is therefore, highly specific and selective., Conclusion: The simultaneous direct quantification of various phenolic acids in different plant extracts was possible with a fast and simple methodology based on PLS-ATR-FTIR analysis., (© 2020 John Wiley & Sons, Ltd.)

A procedure is proposed for the determination of the total amount of sterols in brown algae Bifurcaria bifurcata, Cladostephus hirsitus, Dictyota dichotoma and Cystoseira sedoides, globally determined as fucosterol, which is the major sterol contained in these algae. The method involves the use of cholesterol as reference standard and a correction factor of 1.259+/-0.003, which represents the ratio between the slopes of calibration lines obtained from fucosterol and cholesterol. The method provides precise and accurate results for the IR analysis of real samples.

An analytical procedure was developed for the determination of the total amount of sterols in the red alga Asparagopsis armata, globally determined as cholesterol, which is the major sterol contained in red algae. Samples, previously saponified with KOH were preconcentrated on DSC-18 solid phase cartridges (SPE) and eluted with dichloromethane stabilized with beta-amylene. Fourier transform infrared (FTIR) spectrometry was employed for selective detection at 1049cm(-1) with a baseline established between 1000 and 1079cm(-1). The results were compared to those obtained by high performance liquid chromatography (HPLC). The concentration obtained in actual samples from alga was 3.37% (w/w) by FTIR and 3.30% (w/w) by HPLC, showing a good comparability between the two methods.