Liquid-Phase Microextraction or Electromembrane Extraction?

Abstract

Isolation of substances by liquid-phase microextraction (LPME) or electromembrane extraction (EME) is becoming more and more important in analytical chemistry. However, the understanding of the mass transfer in LPME and EME is limited, especially for highly concentrated samples. In this work, the mass transfer in LPME and EME from aqueous samples (0.5–200 mg L–1) was studied in terms of recovery, equilibrium time, flux, and mass transfer capacity. In both EME and LPME, high recoveries were achieved at low analyte concentration, and the recoveries decreased at high analyte concentration. For EME, the loss in recovery was partly compensated by increasing the extraction voltage (from 50 to 200 V), while the LPME recovery at high analyte concentration was improved by increasing the extraction time (from 30 to 180 min). EME was superior in terms of equilibrium time and flux, while LPME provided much higher mass transfer capacity especially for highly concentrated samples. Moreover, the recovery was much more sensitive to high analyte concentrations in EME than in LPME, and the EME recovery decreased significantly above 50 mg L–1, indicating that LPME could be used to isolate analytes in a wider concentration range than EME. We believe that this fundamental study will be of great importance for the selection of a suitable membrane-based microextraction technique.

Fully Automated Electric-Field-Driven Liquid Phase Microextraction System with Renewable Organic Membrane As a Front End to High Performance Liquid Chromatography

“…Moreover, dynamic LPME resulted in amelioration of the enrichment factors and shortening of the extraction times. Electric-field-driven LPME has also been recently seen as a viable option for expedient SLM extraction of ionizable or polar species, − also in micro/mesofluidic platforms. − Additional advantages of using an electric field are (i) improved selectivity for transfer of ionized species, (ii) efficient matrix cleanup, and (iii) modulation of the sample preparation process for potentially exhaustive extraction of target species. , …”

Nonaqueous Miscible Liquid–Liquid Electroextraction for Fast Exhaustive Enrichment of Ultratrace Analytes by an Exponential Transfer and Deceleration Mechanism

“…However, two important restrictions of current EFASP designs are the requirement for at least two immiscible phases and contact between at least one aqueous phase and the electrode . For example, electromembrane extraction (EME), the most studied EFASP technique in recent years, , features a liquid–liquid–liquid system that typically comprises aqueous donor and acceptor phases separated by a membrane (organic filter). − In supported liquid membranes (SLMs), the organic solvent is immobilized in the pores of a polymeric membrane, whereas free liquid membranes (FLMs) contain the organic solvent between two aqueous phases in a narrow channel . A further example is electroextraction (EE), in which two immiscible phases (i.e., aqueous and organic phases) are employed without membranes .…”

“…Regarding the second restriction, the use of an aqueous phase can adversely impact the accuracy, speed, and applicability of the method. For example, electrolysis , of the aqueous phase is a common and undesired process that leads to bubble formation and production of OH – and H + ions at the cathodic and anodic electrodes, respectively, consequently altering the pH of the donor and acceptor phases. ,, As the pH value governs analyte ionization, , even minor changes in the pH of the acceptor phase may lead to back-extraction through passive diffusion . Although the enrichment factor can be increased by using a small volume of the acceptor phase (e.g., microliter level), the ER is extremely susceptible to electrolytic byproducts. , Furthermore, the higher conductivity of salt-, acid-, or base-containing aqueous phases and the lower partial voltage in the circuit cause slow analyte transmission .…”

“…For example, electrolysis 8,10 of the aqueous phase is a common and undesired process that leads to bubble formation and production of OH − and H + ions at the cathodic and anodic electrodes, respectively, consequently altering the pH of the donor and acceptor phases. 8,24,25 As the pH value governs analyte ionization, 14,26 even minor changes in the pH of the acceptor phase may lead to back-extraction through passive diffusion. 10 Although the enrichment factor can be increased by using a small volume of the acceptor phase (e.g., microliter level), the ER is extremely susceptible to electrolytic byproducts.…”

Versatile Integration of Liquid-Phase Microextraction and Fluorescent Aptamer Beacons: A Synergistic Effect for Bioanalysis

“…24,25 In a typical LPME process, the analyte is first extracted from a sample into a supported liquid membrane (SLM) and further into an acceptor solution. 26 In this process, the low-level target in biological samples can be preconcentrated in the simple acceptor solution, making it a promising technique for future integration with FABs. So far, several miniaturized membranebased LPME setups including in-vial LPME, 27 solvent bar LPME, 28 hollow-fiber LPME, 29 and flat membrane-based LPME (FM-LPME) 30 have been developed.…”