Search

Salicylic acid (SA) is an important stress signaling phytohormone and plays an essential role in physiological processes in plants. SA fractionation has been carried out batchwise, which is not compatible with the high analytical demand in agronomical studies and increases susceptibility to analytical errors. In this context, a novel flow-batch sample preparation system for SA fractionation on fresh plant leaves was developed. It was based on microwave-assisted extraction with water and conversion of the conjugated species to free SA by alkaline hydrolysis. Free and total SA were quantified by fluorimetry after separation by sequential injection chromatography in a C18 monolithic column. The proposed procedure is directly applicable to plant leaves containing up 16 mg kg−1 SA, with a limit of detection of 0.1 mg kg−1 of SA, coefficient of variation of 3.0% (n = 10), and sampling rate of 4 samples h−1. The flow-batch sample preparation system was successfully applied to SA fractionation in sugarcane, corn, and soybean leaves without clogging or increasing in backpressure. The proposed approach is simple, less time-consuming, and more environmentally friendly in comparison to batchwise procedures. [ABSTRACT FROM AUTHOR]

Salicylic acid is an emerging environmental contaminant, usually found at ng/L concentrations in natural waters. Its quantification usually involves liquid chromatography‐tandem mass spectrometry, which requires complex and costly instrumentation as well as time‐consuming sample pretreatment, typically involving large solvent volumes. In this work, sequential injection chromatography was exploited to develop a fast, green, cost‐effective, and highly sensitive procedure for fluorimetric determination of salicylic acid in natural waters. Analyte preconcentration directly on the chromatographic column (on‐column preconcentration) was exploited to improve detectability, yielding an enrichment factor of 122 (1.75 mL of sample) and takes only 8.5 min per determination. A detection limit of 20 ng/L, a linear response range from 0.06 to 5.00 µg/L, coefficients of variation lower than 3.0% (n = 10), and recoveries within 86 and 114% were estimated. The procedure was applied for the analyses of freshwater samples and results agreed with those obtained by liquid chromatography‐tandem mass spectrometry at the 95% confidence level. The proposed procedure encompasses in‐line concentration, isolation/separation, and detection, without the need for sample clean‐up, thus minimizing the consumption of organic solvents and risk of analyte losse. [ABSTRACT FROM AUTHOR]

A novel strategy for preparing polyethylene open tubular reactors coated with MnO2(s) was pioneered for flow analysis in order to minimize the inherent drawbacks of packed solid reagents. As an application, the determination of ascorbic acid in pharmaceuticals was selected. The method involved reduction of Mn(IV) by ascorbic acid, release of the formed Mn2+ion, reaction with formaldoxime, and spectrophotometric monitoring. The influence of flow pattern was investigated by using two similar flow systems relying on constant or pulsed flow delivered by peristaltic or solenoid pumps. With pulsed flow, system versatility and ruggedness were improved, and the analytical sensitivity (0.01143 L mg−1ascorbic acid), detection limit (0.6 mg L−1ascorbic acid), and sampling rate (60 h−1) evaluated compared to constant flow were improved by 2.1%, 40.0%, and 6.5%, respectively. At the same time, the reagent consumption (2.8 mg per determination) and analytical precision (relative standard deviation of approximately 2.5%) were maintained. One can conclude that the mixing conditions did not limit the analyte/reagent interaction. The results were in agreement with the British Pharmacopoeia method. [ABSTRACT FROM AUTHOR]

The main contributions of Brazilian researchers to the field of flow analysis are reviewed, with an emphasis on historical developments, conceptual aspects, system design, and analytical applications. Contributions after the advent of flow injection analysis are highlighted. Novel approaches (e.g. zone merging, zone sampling, zone trapping, multi-site detection, and multi-commutation), flow modalities (e.g. monosegmented flow analysis, flow-batch analysis, multi-pumping flow analysis), as well as the pioneering implementation of different detection techniques (e.g. potentiometry, turbidimetry, flame atomic absorption spectrometry, inductively coupled plasma-optical emission spectrometry, and gravimetry) and analytical steps (e.g. titrations, membrane-less gas diffusion, and electrolytic dissolution) are highlighted. Strategies to improve analytical figures of merit and the use of the flow analyser as a tool for teaching purposes are also discussed. Contributions from Brazilian workers in the context of system miniaturization, “green” chemistry, analysis of complex samples, novel strategies and materials for in-line analyte separation/concentration, and proposals for expert systems are also highlighted. The large-scale analysis of samples of agronomical, environmental, industrial, and clinical relevance is emphasized. [ABSTRACT FROM AUTHOR]

Review: 74 refs. [ABSTRACT FROM AUTHOR]