Programmable Millifluidic Platform Integrating Automatic Electromembrane Extraction Cleanup and In-Line Electrochemical Detection: A Proof of Concept

Electromembrane Extraction in Suspect Screening of Polar Organic Xenobiotics and their Metabolites in Human Urine: A New Approach to Enhance Compound Annotation?

Suspect and nontarget screening (SNTS) methodologies using human urine are invaluable strategies for understanding the human exposome. However, very polar organic compounds are often overlooked in those methods due to challenges in sample preparation and chromatographic analysis. Although "dilute-and-shoot" (DS) followed by mixed-mode liquid chromatography-high-resolution mass spectrometry (MMLC-HRMS) might be deemed suitable, complementary strategies are needed to enhance SNTS and expand compound identification. In this context, the potential of nonsupported microelectromembrane extraction (μ-EME) is thoroughly studied as a supplement to DS-MMLC-HRMS. It was demonstrated that μ-EME-MMLC-HRMS enables the refinement of suspect screening results from a 24 h pooled human urine sample. The selective extraction capability of μ-EME for charged analytes, compared to DS, allowed the identification of 24 false positives and 4 false negatives. The confidence level of 6 suspects was also enhanced through μ-EME interpretation. Moreover, nine suspects were identified exclusively in μ-EME experiments due to the urine cleanup provided by that technique. Notably, suspects containing carboxylic acid groups (phase II metabolites) and amines were particularly well-annotated by μ-EME employing selective extraction conditions for acids and bases, respectively. Thus, μ-EME proves to be a confirmatory dimension in MMLC-based SNTS approaches.

Dual microelectromembrane extraction as a tunable platform for the determination of antioxidant compounds with varied hydrophobicity in oral bioaccessibility assays of food commodities: a proof of concept

An automatic millifluidic dual microelectromembrane extraction (D-µEME) method as a front-end to HPLC-UV-Vis is herein proposed for the first time to facilitate the matrix clean-up of relatively polar polyphenolic acidic (PPA) antioxidants with a relatively broad range of lipophilicity (logP from -0.27 to 2.14) from simulated gastric extracts of oral bioaccessibility tests. The flow setup is amenable to handle microliter volumes of two distinct organic phases along with donor and acceptor phases unsupervised, conduct in-tube D-µEME in parallel without supporting membranes, and mix the two acceptor phases automatically prior to online HPLC-UV-Vis. The target antioxidants involve gallic acid, chlorogenic acid, 4-hydroxybenzoic acid, caffeic acid, and trans-cinnamic acid. Various solvents are explored to investigate their compatibility for simultaneous D-µEME, including 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and 1-nonanol, as well as deep eutectic solvents, e.g., thymol/6-methyl coumarin, and ionic liquids as additives to alcohols. Notably, 1-pentanol and 1-octanol exhibit the best performances in extracting the most polar (gallic acid and chlorogenic acid) and the least polar analytes (trans-cinnamic acid), respectively, notwithstanding both solvents are amenable to retrieve analytes with medium hydrophobicity (4-hydroxybenzoic acid and caffeic acid). The effects of the voltage, the extraction time, and the sample ionic strength on the extraction recoveries are also investigated in detail. Under the selected D-µEME conditions, the overall linear ranges span from 1.25 to 80 mg/L, with limits of detection ranging from 0.2 to 3.3 mg/L. The flow-based D-µEME is resorted to oral bioaccessibility assays in the gastric phase of the target compounds from eggplant, blueberry, and coffee bean extracts, with relative extraction recoveries ranging from 71.5 to 133.5%.

Enhancing the Concentration Capability of Nonsupported Electrically Driven Liquid-Phase Microextraction through Programmable Flow Using an All-In-One 3D-Printed Optosensor: A Proof of Concept

A versatile millifluidic 3D-printed inverted Y-shaped unit (3D-YSU) was prototyped to ameliorate the concentration capability of nonsupported microelectromembrane extraction (μ-EME), exploiting optosensing detection for real-time monitoring of the enriched acceptor phase (AP). Continuous forward-flow and stop-and-go flow modes of the donor phase (DP) were implemented via an automatic programmable-flow system to disrupt the electrical double layer generated at the DP/organic phase (OP) interface while replenishing the potentially depleted layers of analyte in DP. To further improve the enrichment factor (EF), the organic holding section of the OP/AP channel was bifurcated to increase the interfacial contact area between the DP and the OP. Exploiting the synergistic assets of (i) the continuous forward-flow of DP (1050 μL), (ii) the unique 3D-printed cone-shaped pentagon cross-sectional geometry of the OP/AP channel, (iii) the bifurcation of the OP that creates an inverted Y-shape configuration, and (iv) the in situ optosensing of the AP, a ca. 24 EF was obtained for a 20 min extraction using methylene blue (MB) as a model analyte. The 3D-YSU was leveraged for the unsupervised μ-EME and the determination of MB in textile dye and urban wastewater samples, with relative recoveries ≥88%. This is the first work toward analyte preconcentration in μ-EME with in situ optosensing of the resulting extracts using 3D-printed millifluidic platforms.

3D-printed stereolithographic fluidic devices for automatic nonsupported microelectromembrane extraction and clean-up of wastewater samples

BACKGROUND

There is a quest of novel functional and reliable platforms for enhancing the efficiency of microextraction approaches in troublesome matrices, such as industrial wastewaters. 3D printing has been proven superb in the analytical field to act as the springboard of microscale extraction approaches.

RESULTS

In this work, low-force stereolithography (SL) was exploited for 3D printing and prototyping bespoke fluidic devices for accommodating nonsupported microelectromembrane extraction (μEME). The analytical performance of 3D-printed μEME devices with distinct cross-sections, including square, circle, and obround, and various channel dimensions was explored against that of commonly used circular polytetrafluoroethylene (PTFE) tubing in flow injection systems. A computer-controlled millifluidic system was harnessed for the (i) automatic liquid-handling of minute volumes of donor, acceptor, and organic phases at the low μL level that spanned from 3 to 44 μL in this work, (ii) formation of three-phase μEME, (iii) in-line extraction, (iv) flow-through optical detection of the acceptor phase, and (v) solvent removal and regeneration of the μEME device and fluidic lines. Using methylene blue (MB) as a model analyte, experimental results evinced that the 3D-printed channels with an obround cross-section (2.5 mm × 2.5 mm) were the most efficient in terms of absolute extraction recovery (59%), as compared to PTFE tubing of 2.5 mm inner diameter (27%). This is attributed to the distinctive convex interface of the organic phase (1-octanol), with a more pronounced laminar pattern, in 3D-printed SL methacrylate-based fluidic channels against that of PTFE tubing on account of the enhanced 1-octanol wettability and lower contact angles for the 3D-printed devices. The devices with obround channels were leveraged for the automatic μEME and in-line clean-up of MB in high matrix textile dyeing wastewater samples with relative recoveries ≥81%, RSD% ≤ 17.1% and LOD of 1.3 mg L-1. The 3D-printed nonsupported μEME device was proven superb for the analysis of wastewater samples with an elevated ionic strength (0.7 mol L-1 NaCl, 5000 mg L-1 Na2CO3, and 0.013 mol L-1 NaOH) with recorded electric currents below 12 μA.

NOVELTY

The coupling of 3D printing with nonsupported μEME in automatic flow-based systems is herein proposed for the first time and demonstrated for the clean-up of troublesome samples, such as wastewaters.