Smart Titanium Wire Used for the Evaluation of Hydrophobic/Hydrophilic Interaction by In-Tube Solid Phase Microextraction

Abstract

Evaluation of the hydrophobic/hydrophilic interaction individually between the sorbent and target compounds in sample pretreatment is a big challenge. Herein, a smart titanium substrate with switchable surface wettability was fabricated and selected as the sorbent for the solution. The titanium wires and meshes were fabricated by simple hydrothermal etching and chemical modification so as to construct the superhydrophilic and superhydrophobic surfaces. The micro/nano hierarchical structures of the formed TiO2 nanoparticles in situ on the surface of Ti substrates exhibited the switchable surface wettability. After UV irradiation for about 15.5 h, the superhydrophobic substrates became superhydrophilic. The morphologies and element composition of the wires were observed by SEM, EDS, and XRD, and their surface wettabilities were measured using the Ti mesh by contact angle goniometer. The pristine hydrophilic wire, the resulting superhydrophilic wire, superhydrophobic wire, and the UV-irradiated superhydrophilic wire were filled into a stainless tube as the sorbent instead of the sample loop of a six-port valve for on-line in-tube solid-phase microextraction. When employed in conjunction with HPLC, four kinds of wires were comparatively applied to extract six estrogens in water samples. The optimal conditions for the preconcentration and separation of target compounds were obtained with a sample volume of 60 mL, an injection rate of 2 mL/min, a desorption time of 2 min, and a mobile phase of acetonile/water (47/53, v/v). The results showed that both the superhydrophilic wire and UV-irradiated wire had the highest extraction efficiency for the polar compounds of estrogens with the enrichment factors in the range of 20–177, while the superhydrophobic wire exhibited the highest extraction efficiency for the non-polar compounds of five polycyclic aromatic hydrocarbons (PAHs). They demonstrated that extraction efficiency was mainly dependent on the surface wettability of the sorbent and the polarity of the target compounds, which was in accordance with the molecular theory of like dissolves like.

Latest Improvements and Expanding Applications of Solid-Phase Microextraction

“…In the past two years, some reported coating materials have possessed more beautiful and unique microstructures, such as core–shell and hollow structures , and flower-like and helical morphologies. − In addition, the spherical morphology is still the most common, which is generally uniform. , Although these fascinating microstructures have been designed and presented in reported works, there is still a lack of explanation regarding the effects of morphology on the enrichment performance. This needs to be further explored.…”

“Two birds with one stone” strategy for oil/water separation based on Ni foams assembled using metal–organic frameworks

“…It demonstrated that the transformation of surface wettability between SHL&UWSOB and SHB&SOL was necessary for versatile applications. [36][37][38][39]…”

Solid-Phase Microextraction and Related Techniques in Bioanalysis

“…This Special Issue, entitled “Solid-Phase Microextraction and Related Techniques in Bioanalysis”, consists of 14 original, peer-reviewed papers written by research groups worldwide. The topics covered include headspace fiber SPME (HS-SPME) gas chromatography–mass spectrometry (GC-MS) [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ], HS-in-needle ME (HS-INME)-GC-MS [ 9 ], thin film SPME (TF-SPME) liquid chromatography–tandem mass spectrometry (LC-MS/MS) [ 10 ], magnetic solid-phase extraction (MSPE) LC-MS/MS [ 11 ], in-tube SPME (IT-SPME) LC-MS/MS [ 12 , 13 , 14 ] and IT-SPME LC-UV [ 15 ]. The samples analyzed include a wide range of plant-derived volatile organic compounds [ 2 , 3 , 4 , 5 , 6 , 7 ]; body odor from the skin [ 8 , 9 ]; metabolites from urine [ 10 ], plasma [ 11 ] and saliva [ 12 ] samples; biomarkers of exposure to tobacco smoke in hair [ 13 , 14 ]; and environmental estrogens in water [ 15 ].…”

“…Finally, an IT-SPME method using extraction tubes filled with hydrophilic, superhydrophilic, superhydrophobic and UV-irradiated superhydrophilic Ti wires as sorbents was used for on-line IT-SPME LC-UV analysis of six estrogen-like hormones in water samples [ 15 ].…”