Synthesis and application of multi-walled carbon nanotubes–molecularly imprinted sol–gel composite material for on-line solid-phase extraction and high-performance liquid chromatography determination of trace Sudan IV

Nanofiber-based sorbents: Current status and applications in extraction methods

Advanced sorbents gradually become a research hotspot on account of the increasing attention paid to environmental problems. Due to the prominent physicochemical features of nanofibers (NFs), such as high porosity, large surface area, favorable interconnectivity, high adsorption capacity, wettability, and the possibility of surface modification using functional groups, these nanostructures are regarded as excellent candidates for extraction applications. Therefore, the research in the field of NFs and their nanocomposites has been increasing in recent years. In the present review, we summarize the most recent studies on NFs-based sorbents focusing on strategies for preparation, characterization, and their unique capabilities as porous sorbents in various sorbent-based extraction methods. Moreover, we further described the performance and selectivity of sorbents to achieve improved extraction efficiency. Finally, some perspectives on the challenges and outlook are provided to aid future investigations related to this topic.

Insights into the structure-performance relationships of extraction materials in sample preparation for chromatography

Sample preparation is one of the most crucial steps in analytical processes. Commonly used methods, including solid-phase extraction, dispersive solid-phase extraction, dispersive magnetic solid-phase extraction, and solid-phase microextraction, greatly depend on the extraction materials. In recent decades, a vast number of materials have been studied and used in sample preparation for chromatography. Due to the unique structural properties, extraction materials significantly improve the performance of extraction devices. Endowing extraction materials with suitable structural properties can shorten the pretreatment process and improve the extraction efficiency and selectivity. To understand the structure-performance relationships of extraction materials, this review systematically summarizes the structural properties, including the pore size, pore shape, pore volume, accessibility of active sites, specific surface area, functional groups and physicochemical properties. The mechanisms by which the structural properties influence the extraction performance are also elucidated in detail. Finally, three principles for the design and synthesis of extraction materials are summarized. This review can provide systematic guidelines for synthesizing extraction materials and preparing extraction devices.

Adsorption of Sudan-IV contained in oily wastewater on lipophilic activated carbons: kinetic and isotherm modelling

Up to nine kinetic and fourteen isotherm adsorption models are employed to model the adsorption of Sudan IV, a lipophilic model pollutant present in a biphasic mixture of cyclohexane-water system to simulate oily wastewater. Six different modified activated carbons were used as adsorbents. The highest amount adsorbed of Sudan IV was found in the material prepared by successive treatments of the parent commercial activated carbon Norit ROX 0.8 with nitric acid and urea, followed by thermal treatment at 800 °C under continuous flow of nitrogen. Kinetic and isotherm adsorption models can be employed to simulate the process, since the effect of the presence of water in the adsorption of Sudan IV from the cyclohexane phase was found to be negligible, owing to the high lipophilic character of both adsorbent and adsorbate. All kinetic and isotherm coefficients, coupling with statistical parameters (r², adjusted r² and sum of squared errors), are determined by non-linear regression fitting and compared to literature data. The model of Avrami is found to be the most appropriate model to represent the adsorption of the pollutant in any of the six modified carbons tested, the highest value of the kinetic constant being 0.055 min^-1. The isotherm adsorption is well-modelled by using the general isotherm equation of Tóth and the multilayer Jovanović expression for the adsorption of Sudan-IV on that material, resulting in a high monolayer uptake capacity (q_m = 193.6 mg g^-1).

Recent Applications of Molecularly Imprinted Sol-Gel Methodology in Sample Preparation

Due to their selectivity and chemical stability, molecularly imprinted polymers have attracted great interest in sample preparation. Imprinted polymers have been applied for the extraction and the enrichment of different sorts of trace analytes in biological and environmental samples before their analysis. Additionally, MIPs are utilized in various sample preparation techniques such as SPE, SPME, SBSE and MEPS. Nevertheless, molecularly imprinted polymers suffer from thermal (stable only up to 150 °C) and mechanical stability issues, improper porosity and poor capacity. The sol-gel methodology as a promising alternative to address these limitations allowing the production of sorbents with controlled porosity and higher surface area. Thus the combination of molecularly imprinted technology and sol-gel technology can create influential materials with high selectivity, high capacity and high thermal stability. This work aims to present an overview of molecularly imprinted sol-gel polymerization methods and their applications in analytical and bioanalytical fields.

Dummy molecularly imprinted polymer based microplate chemiluminescence sensor for one-step detection of Sudan dyes in egg

The objective of this study is to report a molecularly imprinted polymer-based chemiluminescence method for determination of Sudan dyes. A dummy-template molecularly imprinted polymer capable of recognizing seven Sudan dyes was first synthesized and its recognition mechanism was studied by using computation simulation method. The polymer was coated in the wells of conventional microplate to prepare a chemiluminescence sensor and the assay process consisted of only one sample-loading step prior to signal acquisition. The optimized sensor was used to determine the seven dyes in egg yolk and the results were confirmed with a high performance liquid chromatography. Results showed that this sensor achieved ultrahigh sensitivity (1.0-5.0 pg/mL), rapid assay process (10 min) and satisfactory recovery (70.5%-92.2%). Furthermore, the sensor could be reused for 5 times. Therefore, this sensor could be used as a useful tool for screening the residues of Sudan dyes in egg.

One-pot synthesis of uniform and monodisperse superparamagnetic molecularly imprinted polymer nanospheres through a sol–gel process for selective recognition of bisphenol A in aqueous media

Uniform and monodisperse Fe₃O₄@MIP nanospheres were directly synthesized using a sol–gel method on the surface of Fe₃O₄–COOH spheres.

Modification of cellulose paper with polydopamine as a thin film microextraction phase for detection of nitrophenols in oil samples

Polydopamine cellulose paper was used as a novel extraction phase to detect nitrophenols in oil samples.

Comparison between dispersive liquid–liquid microextraction and ultrasound-assisted nanoparticles-dispersive solid-phase microextraction combined with microvolume spectrophotometry method for the determination of Auramine-O in water samples

Novel dispersive solid phase micro-extraction and dispersive liquid–liquid micro-extraction determination of Auramine-O content in various real samples.

Magnetic nanoparticle based dispersive micro-solid-phase extraction for the determination of malachite green in water samples: optimized experimental design

This paper presents an extraction method based on dispersive-nanoparticle-solid phase microextraction for the preliminary preconcentration and subsequent spectrophotometric determination of trace amounts of malachite green.

Molecular imprinting science and technology: a survey of the literature for the years 2004-2011

Herein, we present a survey of the literature covering the development of molecular imprinting science and technology over the years 2004-2011. In total, 3779 references to the original papers, reviews, edited volumes and monographs from this period are included, along with recently identified uncited materials from prior to 2004, which were omitted in the first instalment of this series covering the years 1930-2003. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by sections describing fundamental aspects of molecular imprinting including the development of novel polymer formats. Thereafter, literature describing efforts to apply these polymeric materials to a range of application areas is presented. Current trends and areas of rapid development are discussed.

Preparation of a core–shell magnetic ion-imprinted polymer via a sol–gel process for selective extraction of Cu(ii) from herbal medicines

A magnetic surface ion-imprinted polymer (c-MMWCNTs-SiO₂-IIP) was synthesized using c-MMWCNTs as the core, 3-ammonium propyltriethoxysilane (APTES) as the functional monomer, tetraethylorthosilicate (TEOS) as the cross-linker and Cu(ii) as the template.

Preparation, characterization and application of thiosemicarbazide grafted multiwalled carbon nanotubes for solid-phase extraction of Cd(II), Cu(II) and Pb(II) in environmental samples

Thiosemicarbazide-grafted multi-walled carbon nanotubes were prepared and employed to investigate the pre-concentration of Cd(II), Cu(II) and Pb(II) from aqueous solution prior to their determination by ICP-OES. The resulting material was characterized by FT-IR, TGA and SEM. Various factors influencing the separation and pre-concentration were investigated. The enrichment factor typically is 60. Under optimized experimental conditions, the maximum adsorption capacities of Cd(II), Cu(II) and Pb(II) were found to be 1.98, 10.94, 3.69 mg/g, and the relative standard deviations are < 3.5% (n = 6). The new adsorbent shows superior reusability and stability. The procedure was successfully applied to the determination of trace quantities of Cd(II), Cu(II) and Pb(II) in water samples.

Dummy molecularly imprinted solid-phase extraction for selective determination of five phthalate esters in plastic bottled functional beverages

In this paper, a highly selective sample cleanup procedure combing dummy molecular imprinting and solid-phase extraction (DMI-SPE) was developed for the simultaneous isolation and determination of five phthalate esters in plastic bottled beverages. The new imprinted microspheres were synthesized via precipitation polymerization using diisononyl phthalate as a dummy template that showed high selectivity and affinity to the five kinds of phthalate esters and were successfully applied as selective sorbents of DMI-SPE for the simultaneous determination of the phthalate esters from plastic bottled beverages. Good linearity was obtained in a range of 5.0-750.0 μg/L, and the average recoveries of the five phthalate esters at three spiked levels ranged from 84.3 to 96.2% with the relative standard deviations less than 5.49%. The developed extraction protocol eliminated the effect of template leakage on quantitative analysis and could be applied for the determination of phthalate esters in complicated functional beverages products.

Selective solid-phase extraction of Sudan I in chilli sauce by single-hole hollow molecularly imprinted polymers

A new single-hole hollow molecularly imprinted polymer (SHH-MIP) was prepared by multistep seed swelling polymerization using Sudan I as template molecule and successfully applied to selective solid-phase extraction (SPE) of Sudan dyes in chilli sauce samples. The polymers possessed high specific surface area obtained by nitrogen adsorption and good thermal stability without decomposition lower than 380 °C by thermogravimetry analysis. Much higher binding capacity was exhibited than with irregular solid MIP prepared by bulk polymerization, because most of the binding sites were located in the surface of the polymers, facilitating template removal and mass transfer. Accordingly, the SHH-MIP was employed as SPE adsorbent for chilli sauce analysis and offered high recoveries for Sudan I in the range of 87.5-103.4% with the precision of 1.94-5.33% at three spiked levels. The SHH-MIP with high selectivity and high stability was demonstrated to be potentially applicable for high selective preconcentration and determination of trace Sudan dyes in complicated samples.