Nonhydrolytic sol-gel approach to facile creation of surface-bonded zirconia organic-inorganic hybrid coatings for sample preparation. Ι. Capillary microextraction of catecholamine neurotransmitters

Aramid-wrapped CNT hybrid sol–gel sorbent for polycyclic aromatic hydrocarbons

This work describes the preparation of an analytical microextraction sorbent using a simple and versatile sol–gel hybrid composite, i.e., aramid oligomers wrapping multi-walled carbon nanotubes (CNTs) covalently bonded to a porous silica network.

A facile and label-free ratiometric optical sensor for selective detection of norepinephrine by combining second-order scattering and fluorescence signals

In this work, a facile and label-free ratiometric sensor is constructed for selective determination of norepinephrine (NE) by coupling second-order scattering (SOS) and fluorescence, two different and independent optical signals. Herein, polyethyleneimine (PEI) dilute solution medium shows an intensive SOS signal without any fluorescence response. Interestingly, NE can be selectively induced by PEI to emit bright fluorescence, and meanwhile causes an observable decrease in the SOS signal due to the interactions between NE and PEI. The simultaneous variation of the two independent signals can be used for ratiometric sensing of NE. Under the optimal conditions, the resultant ratiometric sensor displays high sensitivity and selectivity toward NE by simultaneously monitoring fluorescence and SOS signals with the same excitation wavelength. The proposed sensor exhibits a good linear relationship versus NE concentration in the range of 10.0 nM-45.0 μM with a detection limit of 2.0 nM (S/N = 3) and has been successfully applied to the determination of NE in real samples without the use of any extra reagent. The combination of fluorescence and SOS signals provides a new scheme for ratiometric sensor design, greatly simplifying experimental procedure and effectively enhancing detection accuracy. Moreover, the proposed analytical strategy further broadens the application of dilute solutions of polymers in research into optical sensor and green analytical chemistry. Graphical abstract.

Online Sol-gel Capillary Microextraction-Mass Spectrometry (CME-MS) Analysis of Illicit Drugs

Providing rapid and sensitive sample cleanup, sol-gel capillary microextraction (CME) is a form of solid phase microextraction (SPME). The capillary format of CME couples easily with mass spectrometry (MS) by employing sol-gel sorbent coatings in inexpensive fused silica capillaries. By leveraging the syringe pump and six-port valve readily available on the commercial MS, we can obviate the need for chromatography for samples as complex as urine in quantitative assays. Two different sol-gel materials were studied as microextraction sorbents: one with a single ligand of octadecyl (C₁₈) and the other with a dual-ligand combination of C₁₈ and phenyl (Phe) groups. The CME-MS method was optimized for flow rate and solvent desorption and studied for overall microextraction performance between the two sorbents studied. We extract illicit drugs including cocaine, heroin, amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine, and oxycodone, proving good run-to-run reproducibility (RSD% < 10%) and low detection limits (< 10 ng mL^-1). The dual-ligand sorbent demonstrated superior performance due to typical hydrophobic properties of C₁₈ as well as potential π-π interactions of the Phe functionality and the aromatic moiety common to many drugs. This study demonstrates the advantage of fine-tuning sol-gel sorbents for application-specific CME-MS. We apply our method to the analysis of various drugs in synthetic and human urine samples and show low carryover effect (~ 5%) and low matrix effect in the presence of the urine matrix. Thus, the sol-gel CME-MS technique described herein stands to be an attractive alternative to other SPME-MS techniques.

Sol-gel niobia sorbent with a positively charged octadecyl ligand providing enhanced enrichment of nucleotides and organophosphorus pesticides in capillary microextraction for online HPLC analysis

A niobia-based sol-gel organic-inorganic hybrid sorbent carrying a positively charged C₁₈ ligand (Nb₂ O₅ -C₁₈ (+ve)) was synthesized to achieve enhanced enrichment capability in capillary microextraction of organophosphorus compounds (which include organophosphorus pesticides and nucleotides) before their online analysis by high-performance liquid chromatography. The sorbent was designed to simultaneously provide three different types of molecular level interactions: electrostatic, Lewis acid-base, and van der Waals interactions. To understand relative contributions of various molecular level analyte-sorbent interactions in the extraction process, two other sol-gel niobia sorbents were also created: (a) a purely inorganic sol-gel niobia sorbent (Nb₂ O₅ ) and (b) an organic-inorganic hybrid sol-gel niobia sorbent carrying an electrically neutral-bonded octadecyl ligand (Nb₂ O₅ -C₁₈ ). The extraction efficiency of the created sol-gel niobia sorbent (Nb₂ O₅ -C₁₈ (+ve)) was compared with that of analogously designed and synthesized titania-based sol-gel sorbent (TiO₂ -C₁₈ (+ve)), taking into consideration that titania-based sorbents present state-of-the-art extraction media for organophosphorus compounds. In capillary microextraction with high-performance liquid chromatography analysis, Nb₂ O₅ -C₁₈ (+ve) had shown 40-50% higher specific extraction values (a measure of extraction efficiency) over that of TiO₂ -C₁₈ (+ve). Compared to TiO₂ -C₁₈ (+ve), Nb₂ O₅ -C₁₈ (+ve) also provided superior analyte desorption efficiency (96 vs. 90%) during the online release of the extracted organophosphorus pesticides from the sorbent coating in the capillary microextraction capillary to the chromatographic column using reversed-phase high-performance liquid chromatography mobile phase.

Tantala-based sol-gel coating for capillary microextraction on-line coupled to high-performance liquid chromatography

A sol-gel organic-inorganic hybrid sorbent, consisting of chemically integrated tantalum (V) ethoxide (TaEO) and polypropylene glycol methacrylate (PPGM), was developed for capillary microextraction (CME). The sol-gel sorbent was synthesized within a fused silica capillary through hydrolytic polycondensation of TaEO and chemical incorporation of PPGM into the evolving sol-gel tantala network. A part of the organic-inorganic hybrid sol-gel network evolving in the vicinity of the capillary walls had favorable conditions to get chemically bonded to the silanol groups on the capillary surface forming a surface-bonded coating. The newly developed sol-gel sorbent was employed to isolate and enrich a variety of analytes from aqueous samples for on-line analysis by high-performance liquid chromatography (HPLC) equipped with a UV detector. CME was performed on aqueous samples containing trace concentrations of analytes representing polycyclic aromatic hydrocarbons, ketones, alcohols, amines, nucleosides, and nucleotides. This sol-gel hybrid coating provided efficient extraction with CME-HPLC detection limits ranging from 4.41pM to 28.19 pM. Due to direct chemical bonding between the sol-gel sorbent coating and the fused silica capillary inner surface, this sol-gel sorbent exhibited enhanced solvent stability. The sol-gel tantala-based sorbent also exhibited excellent pH stability over a wide pH range (pH 0-pH 14). Furthermore, it displayed great performance reproducibility in CME-HPLC providing run-to-run HPLC peak area relative standard deviation (RSD) values between 0.23% and 3.83%. The capillary-to-capillary RSD (n=3), characterizing capillary preparation method reproducibility, ranged from 0.24% to 4.11%. The results show great performance consistency and application potential for the sol-gel tantala-PPGM sorbent in various fields including biomedical, pharmaceutical, and environmental areas.