Fully automated on-line flow-batch based ultrasound-assisted surfactant-mediated extraction and determination of anthraquinones in medicinal plants

Green Extraction Processes for Complex Samples from Vegetable Matrices Coupled with On-Line Detection System: A Critical Review

The detection of analytes in complex organic matrices requires a series of analytical steps to obtain a reliable analysis. Sample preparation can be the most time-consuming, prolonged, and error-prone step, reducing the reliability of the investigation. This review aims to discuss the advantages and limitations of extracting bioactive compounds, sample preparation techniques, automation, and coupling with on-line detection. This review also evaluates all publications on this topic through a longitudinal bibliometric analysis, applying statistical and mathematical methods to analyze the trends, perspectives, and hot topics of this research area. Furthermore, state-of-the-art green extraction techniques for complex samples from vegetable matrices coupled with analysis systems are presented. Among the extraction techniques for liquid samples, solid-phase extraction was the most common for combined systems in the scientific literature. In contrast, for on-line extraction systems applied for solid samples, supercritical fluid extraction, ultrasound-assisted extraction, microwave-assisted extraction, and pressurized liquid extraction were the most frequent green extraction techniques.

Systematic evaluation of sample preparation for fractionation of phytohormone salicylic acid in fresh leaves

The determination of salicylic acid (SA), an important phytohormone responsible for stress signaling in plants, is of great importance in agricultural studies. However, a critical evaluation of the procedures for the extraction of the analytes and hydrolysis of the conjugated forms of SA is lacking in the literature and the available alternatives are complex, time-consuming, and laborious. In this study, the sample preparation methods for SA fractionation were critically evaluated to develop a simpler and faster alternative procedure. Microwave-assisted extractions were carried out with 2.0 g of fresh leaves and 8.0 mL of a 75% v/v ethanol:water solution at 40 °C for 10 min, followed by alkaline hydrolysis using 100 μL of 0.1 mol L-1 NaOH at 80 °C for 60 min. Free and total SA were determined in crude and hydrolyzed extracts, respectively, by fluorimetry after chromatographic separation of the sample matrix under isocratic elution (25% v/v acetonitrile/phosphate buffer) using a C18 column. Recovery experiments using methyl salicylate and acetylsalicylic acid model compounds demonstrated that the soft microwave-assisted extraction did not decompose the SA derivatives and that alkaline hydrolysis was quantitative. The proposed procedure was successfully applied for fractionation of SA in sugarcane, corn, and soybean leaves with extraction and hydrolysis yields up to 70 and 20% higher than those achieved in previously proposed approaches, respectively. The developed procedure is a simple, fast, and reliable alternative for SA fractionation in crude extracts without sample clean-up, and utilizes dilute reagents and green solvents.

Optimization of Ultrasonic-Assisted Extraction and Purification of Rhein from Cassia fistula Pod Pulp

Rhein is used as an active ingredient in laxatives in medicinal herbal products and is a chemical marker for quality control purposes. Thus, a simple and effective method for the optimized extraction of a high amount of rhein from the fruit pulp of Cassia fistula was investigated using ultrasonic-assisted extraction (UAE). The response surface methodology was applied to find the most suitable parameters for optimizing the extraction process and to study the factors’ relationships with each other. The best conditions for ultrasonic extraction were the application of 1:40 g/mL solid-to-liquid ratio and 10% EtOH–H₂O as a solvent at 75 °C for 40 min. This method was compared to a conventional decoction in two variations. In these experiments, it was confirmed that the UAE was more favorable than the decoction methods. The resulting crude extract was further purified by liquid–liquid extraction with a basic pH adjustment, followed by recrystallization. High-purity rhein was obtained by using chromatographic techniques and nuclear magnetic resonance spectroscopy. Therefore, this study suggests that UAE is an efficient alternative method for the extraction of rhein from C. fistula pod pulp. The resulting optimized conditions can be applied as a useful tool for the large-scale industrial production of a rhein-rich plant extract.

Vapor permeation-stepwise injection simultaneous determination of methanol and ethanol in biodiesel with voltammetric detection

A novel vapor permeation-stepwise injection (VP-SWI) method for the determination of methanol and ethanol in biodiesel samples is discussed. In the current study, stepwise injection analysis was successfully combined with voltammetric detection and vapor permeation. This method is based on the separation of methanol and ethanol from a sample using a vapor permeation module (VPM) with a selective polymer membrane based on poly(phenylene isophtalamide) (PA) containing high amounts of a residual solvent. After the evaporation into the headspace of the VPM, methanol and ethanol were transported, by gas bubbling, through a PA membrane to a mixing chamber equipped with a voltammetric detector. Ethanol was selectively detected at +0.19 V, and both compounds were detected at +1.20 V. Current subtractions (using a correction factor) were used for the selective determination of methanol. A linear range between 0.05 and 0.5% (m/m) was established for each analyte. The limits of detection were estimated at 0.02% (m/m) for ethanol and methanol. The sample throughput was 5 samples h(-1). The method was successfully applied to the analysis of biodiesel samples.