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

Abstract

Conventional electrical-field-assisted sample preparation (EFASP) methods rely on analyte transfer between immiscible phases and require at least one aqueous phase in contact with the electrode. In this paper, we report a novel nonaqueous miscible liquid–liquid electroextraction (NMLEE) technique that enables fast exhaustive enrichment of ultratrace analytes from a milliliter-level donor in a vial to a microliter-level acceptor in a tube. Miscible nonaqueous solvents are used for the donor and acceptor to overcome common EFASP problems such as high charge or mass transfer resistance, loss of analytes in the membrane phase, water electrolysis, back-extraction, bubble generation, and difficulties in the application of high voltage for fast migration. According to theoretical derivation and experimental verification results, the concentrations of analytes in the donor and their migration velocity in the acceptor both decrease exponentially with time, and the extraction recovery correlates linearly with the current variation. These mechanisms result in efficient enrichment by forming an analyte-enriched zone and allow the extraction progress and recovery to be monitored and estimated based on the current variation. NMLEE was coupled with liquid chromatography–mass spectrometry to analyze 10 amphetamine-type drugs, atropine, nortriptyline, and methadone in blood and urine samples. This method provided low limits of detection (0.003–0.1 ng·mL–1), satisfactory extraction recoveries (89.6–104.1%), and RSDs (<12.3% for intraday and <8.8% for interday), which met the requirements of the ICH guidelines. This study may contribute to the further development of EFASP methods for effective ultratrace analyses in forensic science.

Nonaqueous Electroextraction with Tunable Selectivity for Direct, Fast, and Exhaustive Enrichment of Per- and Polyfluoroalkyl Acids from Oils and Food Contact Materials

“…Herein, we first achieved this goal based on a nonaqueous electroextraction technique that we reported recently, which is termed nonaqueous miscible liquid−liquid electroextraction (NMLEE). 28 It was the first report on PFAA analysis, as well as oil sample analysis, using EFASP, introducing a powerful approach for routine oil analysis. Unlike EME, NMLEE is based on a totally nonaqueous two-phase system that is born to have good compatibility with water-insoluble samples (e.g., oily samples).…”

“…However, in NMLEE, the ability to sample cleanup and selectivity for analytes are still unclear and questionable. 28 In this study, we attempted to develop an NMLEE method that features high selectivity and inclusivity for PFAA extraction, as well as a universal calibration principle, without MMC or IS. Through further theoretical and experimental investigation into the extraction mechanism of 18 PFAAs and 11 FAs, the selectivity of NMLEE was discovered, which enabled NMLEE to specifically recognize and exhaustively extract PFAAs from a multitude of ICs, despite the concentration of ICs being more than 1000-fold than those of PFAAs.…”

“…NMLEE was first introduced in 2021, and it was confirmed to be an amazing mechanism of fast exhaustive extraction. 28 However, the aim of this study is to reveal and explain the hidden selectivity of NMLEE. The selectivity of NMLEE comes from the utilization of an electric field and, more importantly, its unique extraction mechanism.…”

“…The faster analytes move in DP, the more analytes are extracted in AP within a limited time, resulting in an increase in ER or a reduction in time consumption to achieve exhaustive extraction. Once analytes enter AP, they soon decelerate (tend to stop) and cluster into an analyte-enriched zone with a high enrichment factor, 28 making it possible to achieve similar extraction results of different PFAAs.…”

“…Further, E D can be calculated as eq 3 according to the relationship between the electric potential and field strength. 28…”