Surface Nanodroplet-Based Extraction Combined with Offline Analytic Techniques for Chemical Detection and Quantification

Abstract

Liquid−liquid extraction based on surface nanodroplets can be a green and sustainable technique to extract and concentrate analytes from a sample flow. However, because of the extremely small volume of each droplet (<10 fL, tens of micrometers in base radius and a few or less than 1 μm in height), only a few in situ analytical techniques, such as surfaceenhanced Raman spectroscopy, were applicable for the online detection and analysis based on nanodroplet extraction. To demonstrate the versatility of surface nanodroplet-based extraction, in this work, the formation of octanol surface nanodroplets and extraction were performed inside a 3 m Teflon capillary tube. After extraction, surface nanodroplets were collected by injecting air into the tube, by which the contact line of surface droplets was collected by the capillary force. As the capillary allows for the formation of ∼10 12 surface nanodroplets on the capillary wall, ≥2 mL of octanol can be collected after extraction. The volume of the collected octanol was enough for the analysis of offline analytical techniques such as UV−vis, GC-MS, and others. Coupled with UV−vis, reliable extraction and detection of two common water pollutants, triclosan and chlorpyrifos, was shown by a linear relationship between the analyte concentration in the sample solution and UV−vis absorbance. Moreover, the limit of detection (LOD) as low as 2 × 10 −9 M for triclosan (∼0.58 μg/L) and 3 × 10 −9 M for chlorpyrifos (∼1.05 μg/L) could be achieved. The collected surface droplets were also analyzed via gas chromatography (GC) and fluorescence microscopy. Our work shows that surface nanodroplet extraction may potentially streamline the process in sample pretreatment for sensitive chemical detection and quantification by using common analytic tools.

Microfluidic Detection and Analysis of Microplastics Using Surface Nanodroplets

“…During the solvent exchange, mixing between solutions A and B creates an oversaturation of the oily compound that drives nucleation and growth of surface nanodroplets . Surface nanodroplets have been extensively studied over the past decade with various applications in material synthesis, , liquid–liquid extraction, ,, or chemical detection. , …”

Nanoextraction based on surface nanodroplets for chemical preconcentration and determination

“…In addition to in situ analysis, the surface nanodroplets with extracted analytes in a 3-m hydrophobic capillary tube could be collected (total volume !2 μL) for ex situ detection. 79 The collection of surface nanodroplets is governed by the capillary force between water and air [Figs. 4(a) and 4(b)].…”

Nanoextraction based on surface nanodroplets for chemical preconcentration and determination

“…The target compound in a suspension sample is steadily extracted into the surface nanodroplets. Although part of solid particles is adsorbed and aggregated at the droplet-water interface, their influence on the extraction 79 Copyright 2022 American Chemical Society. Panel (D) and (E) reproduced with the permission from ref.…”

“…In addition to in-situ analysis, the surface nanodroplets with extracted analytes in a 3-meter hydrophobic capillary tube could be collected (total volume ≥ 2 µL) for ex-situ detection. 79 The collection of surface nanodroplets is governed by the capillary force between water and air (Fig. 4A,B).…”

“…(C) UV-Vis absorbance spectra of collected octanol droplets after the extraction from aqueous sample flow with chlorpyrifos concentrations from 2 × 10 −8 M to 10 −6 M. (D) Schemetic illustraion showing the fomarion process of the surface nanodroplets in an evaporating liquid film (E) FTIR spectra of octanol droplets after extraction of 10 −3 M nonanoic acid, octanol, and nonanoic acid. Panel (A), (B), and (C) taken from ref 79. Copyright 2022 American Chemical Society.…”