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In flow analysis, use of a steady and pulseless flow was considered essential for ensuring a reproducible handling of the flowing sample. To this end, peristaltic and syringe pumps have been the propelling device in the vast majority of the flow analysers. Recently, the number of applications involving pulsed flow has been increasing. Most of them refer to use of solenoid pumps, the essence of the so-called multi-pumping flow systems. This review critically discusses the characteristics, potentialities and limitations of the pulsed flow systems, emphasizing the main advantageous characteristics of the streams involved, such as high radial mass transference and good mixing of the fluids. Diverse contributions ranging from instrumentation development to analytical applications are presented., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A novel strategy for accomplishing zone trapping in flow analysis is proposed. The sample and the reagent solutions are simultaneously inserted into convergent carrier streams and the established zones merge together before reaching the detector, where the most concentrated portion of the entire sample zone is trapped. The main characteristics, potentialities and limitations of the strategy were critically evaluated in relation to an analogous flow system with zone stopping. When applied to the spectrophotometric determination of nitrite in river waters, the main figures of merit were maintained, exception made for the sampling frequency which was calculated as 189 h(-1), about 32% higher relatively to the analogous system with zone stopping. The sample inserted volume can be increased up to 1.0 mL without affecting sampling frequency and no problems with pump heating or malfunctions were noted after 8-h operation of the system. In contrast to zone stopping, only a small portion of the sample zone is halted with zone trapping, leading to these beneficial effects., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Abstract Mechanization of separation and preconcentration processes by flow analysis is noteworthy due to improved precision, low consumption of reagents and samples, as well as lower risks to the analyst, of analyte losses, and contamination. The low efficiency of gas diffusion may however limit the sensitivity of flow-based procedures involving gas-liquid separation. This paper deals with the evaluation of potentialities and limitations of a flow analyzer exploiting a new strategy for gas-liquid separation. The manifold comprised a lab-made syringe pump connected to a separation chamber and solenoid valves for solution management. Gas diffusion without barriers for phase separation was implemented inside the chamber under an air flux, followed by the transference of headspace towards an acceptor/derivatization solution inside the syringe. The innovation was exploited for the determination of dissolved inorganic carbon in natural waters. Sample and an acidic solution were aspirated to the chamber and the generated CO 2 was directed towards a bromothymol blue solution, whose color change was monitored by spectrophotometry. A linear response range was attained within 0.5 and 5.0 mg L−1, with limit of detection of 0.25 mg L−1, variation coefficient < 5% (n = 10), and sampling rate of 12 h−1. An 11.5-fold increase in sensitivity was attained with the proposed procedure in relation to the analogous membrane-based procedure. Results for the analysis of river waters agreed with those attained by the reference procedure at the 95% confidence level. Highlights • A general approach to increase efficiency of gas diffusion • Gas-liquid separation without any physical barrier • Twelve-fold increase in sensitivity in relation to the membrane-based procedure • Manifold comprising a single-syringe pump, a separation chamber and solenoid valves [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]