Quantitative NMR analysis of L-Dopa in seeds from two varieties of Mucuna pruriens.

INTRODUCTION: L-Dopa, a key neurotransmitter used to treat neural disorders such as Parkinson's disease, is found in the seeds of the genus Mucuna at a sufficient concentration for possible commercial use. OBJECTIVE: To develop a simple and reliable method to extract L-Dopa from M. pruriens seeds in an aqueous medium and then quantitate this compound using a 1 H qNMR method (internal standard); and also to evaluate the accuracy and reproducibility of this method with an NMR calibration curve. METHODOLOGY: The extraction method of L-Dopa from M. pruriens was optimized. The quantitation with single point quantitative NMR (qNMR) and NMR calibration curve was based on the resonance properties of the main functional groups of the L-Dopa molecule, in particular the signals of the three aromatic protons, which were compared with the signal of an internal standard such as syringic acid. The accuracy (precision and trueness) and reproducibility of both NMR techniques were evaluated. RESULTS: The methods of single point qNMR and NMR calibration curve, applied to the seeds of two M. pruriens varieties, gave very similar L-Dopa contents: 3.0-3.2% and 3.0-3.1%, respectively. CONCLUSION: The statistical analysis confirmed the accuracy and reproducibility of this single point qNMR method (internal standard) for determining L-Dopa, as well as other commercial preparations of this species, without performing an NMR calibration curve.

Quantification of oleacein and oleuropein aglycone in olive oil using deuterated surrogates by normal-phase ultra high performance liquid chromatography with quadrupole time-of-flight mass spectrometry.

An analytical method for the analysis of relevant secoiridoid-based components in olive oil, oleacein and oleuropein aglycone, is described using for the first time deuterated surrogates. 0.2 g of sample was necessary to perform the analysis using liquid-liquid extraction and ultrasound-assisted extraction with a mixture of methanol/water (4:1, v/v). To avoid the formation of by-products, normal-phase ultra high performance liquid chromatography was chosen for the chromatographic separation. The selected mobile phase was a gradient mixture of tetrahydrofurane and hexane, and an ACE Excel 3 CN-ES column as stationary phase. The detection and quantification was performed with a SYNAPT G2-Si mass spectrometer. The calibration curves for oleacein and oleuropein aglycone were linear and quadratic, respectively. The validation was done at three levels of concentration. Relative errors from 0.1 to 10.5% and relative standard deviations lower than 9% were obtained. The method was applied to study different samples of olive oil.

Direct determination of phenolic secoiridoids in olive oil by ultra-high performance liquid chromatography-triple quadruple mass spectrometry analysis.

In recent years, a large number of biological properties and an important role in the organoleptic characteristics of olive oil have been attributed to phenolic secoiridoids, such as oleacein, oleocanthal, oleuropein aglycone and ligstroside aglycone. Consequently, quantifying them is of great interest for the olive oil sector. Currently, there is no consensus in which analytical method must be use to accurately determine these compounds in olive oil, mainly owing to the lack of reference standards for calibration. In this work, analytical standards of phenolic secoiridoids have been used to develop a quantitative and rapid analytical method by UHPLC-MS/MS, in which sample extraction is not carried out. Simple dilutions of the sample with dry tetrahydrofuran and dry acetonitrile were performed before analysing them. It is worth noting that under these conditions the generation of artefacts such as acetals and hemiacetals of the aldehydic forms is highly reduced. The detection and quantification was performed with a Xevo TQS tandem quadrupole mass spectrometer. The method was validated at four concentration levels and finally applied to six samples of extra virgin olive oil.