On-line molecularly imprinted solid phase extraction for the selective spectrophotometric determination of catechol

CoFe-MOF nanoarray as flexible microelectrode for electrochemical detection of catechol in water samples

A simple, selective, and straightforward enzyme-free electrochemical sensor has been designed and developed using cobalt hexacyanoferrate metal-organic framework (CoFe-MOF) nanoarray. The prepared CoFe-MOF nanoarray has been successfully grown over a carbon cloth (CC) to form CoFe-MOF/CC as a flexible microelectrode for the detection of catechol. The surface of the activated CC was covered uniformly with CoFe-MOF in the form of nanoarray and exhibited double-shelled cubic morphology. The CoFe-MOF/CC nanoarray microelectrode showed a pair of well-defined redox peaks corresponding to the [Fe(CN)6]4-/3- redox signal. Interestingly, the fabricated nanoarray microelectrode has displayed superior peak current at lower onset potential with high electrochemical response compared to unmodified potassium hexacyanoferrate (K3 [Fe(CN)6]) over CC microelectrode and bare activated CC. Further, the developed CoFe-MOF/CC nanoarray microelectrode for the oxidation of catechol was examined with consecutive injections of catechol. A fast and noticeable improvement in oxidation peak current was observed, thus representing the excellent electrocatalytic oxidation of catechol at the modified nanoarray microelectrode. Besides, CoFe-MOF/CC microelectrode exhibits an excellent linear response over a concentration range from 0.005 to 2.8 mM with low detection limit (LOD) and high sensitivity of 0.002 mM (S/N = 3) and 205.99 μA/mM, respectively. Moreover, the prepared nonenzymatic sensor showed outstanding stability, acceptable reproducibility, and repeatability, along with good interference ability. Catechol in spiked water samples was successfully quantified.

In-situ synthesized MgIn2S4/CdWO4 type-II heterojunction as a light-driven photoelectrochemical sensor for ultrasensitive detection of catechol in environmental water samples

As an essential chemical intermediate, catechol (CC) residues may have adverse effects on human health. Herein, an effective and facile photoelectrochemical sensor platform based on MgIn2S4/CdWO4 composite is constructed for monitoring CC. MgIn2S4 increases light absorption range and activity, while CdWO4 enhances photoelectronic stability, and the type-II heterojunction formed can significantly enhance photocurrent response. Due to the autoxidation process, CC is converted into oligomeric products, which increase the spatial site resistance and attenuate the overall photocurrent response. It is worth noting that the cauliflower-like structure of MgIn2S4 can provide a large specific surface area, and the presence of Mg2+ promotes autoxidation, thus providing a suitable condition for detecting CC. Under optimal conditions, the MgIn2S4/CdWO4/GCE photoelectrochemical sensor has a prominent linear relationship in the range of CC concentration from 2 nM to 7 μM, with a limit of detection of 0.27 nM. With satisfactory selectivity, excellent stability, and remarkable reproducibility, this sensor provides a crucial reference value for effectively and rapidly detecting pollutants in environmental water samples.

Solid-Phase Extraction of Active Compounds from Natural Products by Molecularly Imprinted Polymers: Synthesis and Extraction Parameters

Molecularly imprinted polymers (MIPs) are synthetic polymers with a predetermined selectivity for a particular analyte or group of structurally related compounds, making them ideal materials for separation processes. Hence, in sample preparation, MIPs are chosen as an excellent material to provide selectivity. Moreover, its use in solid-phase extraction, also referred to as molecular imprinted solid phase extraction (MISPE), is well regarded. In recent years, many papers have been published addressing the utilization of MIPs or MISPE as sorbents in natural product applications, such as synthesis. This review describes the synthesis and characterization of MIPs as a tool in natural product applications.

Cobalt-imidazole metal-organic framework loaded with luminol for paper-based chemiluminescence detection of catechol with use of a smartphone

Chemiluminescence (CL) reagent luminol was loaded into the porous structure of cobalt-imidazole metal-organic framework (MOF) ZIF-67 to obtain luminol-functionalized ZIF-67 (luminol@ZIF-67) with CL property. The morphology, composition, CL property, and CL mechanism of luminol@ZIF-67 were carefully investigated. The obtained luminol@ZIF-67 exhibited strong, stable, and visible CL emission that reacted with H₂O₂, attributed to the strong catalytic effect of ZIF-67 combined with the shortened diffusion distance between luminol and the catalytic center. The CL intensity of luminol@ZIF-67 was more than 550 times higher than that of luminol. Catechol can effectively quench the CL emission of luminol@ZIF-67 that reacted with H₂O₂. Then, a simple paper-based CL imaging detection method was developed for the detection of catechol by using a smartphone as a portable detector. The linear calibration curve of the developed CL assay for catechol ranged from 5 to 100 mg/L with detection limit of 1.1 mg/L (S/N = 3δ). The strong CL emission of luminol@ZIF-67 combined with the effective quench ability of catechol guaranteed high sensitivity of the detection method. The practical application ability of the developed CL assay was tested by the determination of catechol in tea and tap water samples, resulting in acceptable results. This work provides an effective paper-based CL detection method for catechol and enriches the species of the chemiluminescent MOF material.

Glassy carbon electrode modified with hybrid nanofibers containing carbon nanotubes trapped in chitosan for the voltammetric sensing of nicotine at biological pH

In this paper, nicotine (NIC) was detected by cyclic voltammetry (CV) using a modified glassy carbon (GC) electrode. To do this, the surface of the GC electrode was modified by hybrid nanofiber obtained from the electrospinning method. Hybrid nanofibers were produced through the dispersion of carboxylated multi-walled carbon nanotube (MWCNT-COOH) as an inorganic component in the chitosan (CS) polymer matrix as an organic component. The nanofibers showed unique morphology and high surface area value. With the increase of functionalized carbon nanotube content in the nanofibers, the mean pore diameter and average nanofiber diameter increased. The electrochemical properties of nanofibers towards the sensing of NIC were investigated by the CV method. NIC was irreversibly reduced with the use of a CS/MWCNT-COOH electrode, a controlled process with two protons and two electrons. An oxidation signal at lower potential with higher current was obtained for NIC with the use of a polymer-modified electrode compared to a GC electrode. This was as a result of the electrocatalytic effect of the hybrid nanofibers due to the ability of carbon nanotubes to increase the rate of electron transfer. Under optimum conditions, the oxidation of NIC occurred at 0.82 eV with a pH of 7.4. The linear calibration curve was in the concentration range of 0.1-100 μM NIC (R ² = 0.9987) with a detection limit of 30 nM. For 100 parallel 10 μM NIC diagnoses for five replicates, 97.2% with a standard deviation of 4.08 maintained their stability over the first cycle. This indicates that the CS/MWCNT-COOH electrode has excellent reproducibility and stability.

Simultaneous biosensing of catechol and hydroquinone via a truncated cube-shaped Au/PBA nanocomposite

A simultaneous testing of the trace catechol (CC) and hydroquinone (HQ) was achieved via an ultrasensitive phenolic biosensor constructed by the truncated cube-shaped gold/Prussian blue analogue (Au/PBA) nanocomposites. A facile charge-assembly strategy was developed to drive the successive mutual attractions for the crystallization among [Fe(CN)₆]^3-, Co²⁺, and [AuCl₄]^- reactants, benefiting the in-situ growth of Au nanoparticles on all faces of the PBA truncated nanocubes. On account of this special architecture, numerous 10 nm Au particles can rapidly gather the electrons from the enzyme reaction to a PBA crystal due to their high conductivity, and then the current signals will be significantly magnified through the reversible redox of the PBA. Using this nanomaterial, the as-prepared biosensor has shown an extreme wide linear range (CC: 0.2-550 µM, HQ: 1-550 µM) and an ultralow detection limit (CC: 0.06 ± 0.001 µM, HQ: 0.3 ± 0.007 µM) for the independent detections of CC and HQ. More importantly, when the two targets coexist, this biosensor can simultaneously exhibit the obvious and accurate responses of CC and HQ at the different potentials (0.17 V for CC and 0.07 V for HQ) with the high sensitivities and rare mutually interferences.

Date stone based activated carbon/graphite electrode for catechol analysis: physico-chemical properties and application in beverage samples

The purpose of this paper is the modification of a carbon paste electrode (CPE) with activated carbon synthesized from date stones using a pyrolysis system followed by physical activation.

Synthesis and application of bismuth ferrite nanosheets supported functionalized carbon nanofiber for enhanced electrochemical detection of toxic organic compound in water samples

Recently, the multiferroic material has fabulous attention in numerous applications owing to its excellent electronic conductivity, unique mechanical property, and higher electrocatalytic activity, etc. In this paper, we reported that the synthesis of bismuth ferrite (BiFeO₃) nanosheets integrated functionalized carbon nanofiber (BiFeO₃ NS/F-CNF) nanocomposite using a simple hydrothermal technique. Herein, the structural changes and crystalline property of prepared BiFeO₃ NS/F-CNF nanocomposite were characterized using Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). From this detailed structural evolution, the formation of nanosheets like BiFeO₃ and its nanocomposite with F-CNF were scrutinized and reported. Furthermore, the as-prepared BiFeO₃ NS/F-CNF nanocomposite modified glassy carbon electrode (GCE) was applied for electrochemical detection of catechol (CC). As expected, BiFeO₃ NS/F-CNF/GCE shows excellent electrocatalytic activity as well as 3.44 (F-CNF/GCE) and 7.92 (BiFeO₃ NS/GCE) fold higher electrochemical redox response for CC sensing. Moreover, the proposed sensor displays a wide linear range from 0.003 to 78.02 µM with a very low detection limit of 0.0015 µM. In addition, we have validated the real-time application of our developed CC sensor in different water samples.

N-Doped Ordered Mesoporous Carbon Originated from a Green Biological Dye for Electrochemical Sensing and High-Pressure CO2 Storage

Herein, a series of nitrogen-doped ordered mesoporous carbons (NOMCs) with tunable porous structure were synthesized via a hard-template method with a green biological dye as precursor, under various carbonization temperatures (700-1100 °C). Compared with the ordered mesoporous silica-modified and unmodified electrodes, the use of electrodes coated by NOMCs (NOMC-700-NOMC-1100) resulted in enhanced signals and well-resolved oxidation peaks in electrocatalytic sensing of catechol and hydroquinone isomers, attributable to NOMCs' open porous structures and increased edge-plane defect sites on the N-doped carbon skeleton. Electrochemical sensors using NOMC-1000-modified electrode were fabricated and proved feasible in tap water sample analyses. The NOMCs were also used as sorbents for high-pressure CO2 storage. The NOMC with the highest N content exhibits the best CO2 absorption capacities of 800.8 and 387.6 mg/g at 273 and 298 K (30 bar), respectively, which is better than those of other NOMC materials and some recently reported CO2 sorbents with well-ordered 3D porous structures. Moreover, this NOMC shows higher affinity for CO2 than for N2, a benefit of its higher nitrogen content in the porous carbon framework.

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.

Flow analysis in Brazil: contributions over the last four decades

Timeline with the main contributions of Brazilian researchers to flow analysis.

Biomimetic sensor for certain phenols employing a copper(II) complex

A new dimeric Cu(II) complex [Cu(mu(2)-hep)(hep-H)](2).2PF(6) (1) containing a bidentate (hep-H = 2-(2-hydroxyethyl)pyridine) ligand was synthesized and characterized by single crystal X-ray diffraction studies. Each Cu ion in 1 is in a distorted square pyramidal geometry. Further 1 is used as a modifier in the construction of a biomimetic sensor for determining phenols [phenol (Phe), resorcinol (Res), hydroquinone (HQ), and catechol (Cat)] in phosphate buffer by using cyclic voltammetry (CV), chronocoulometry, electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and square wave voltammetry (SWV). DPV has been proposed for trace determination of Phe and Res while SWV for HQ and Cat. The method has been applied for the selective and precise analysis of Phe in commercial injections, Res in hair coloring agents, HQ in photographic developers and cosmetics, and Cat in tea samples and guarana tablets. The calibration curves showed a linear response ranging between 10(-6) and 10(-8) M for all four of the analytes with detection limits (3sigma) of 1.04 x 10(-8), 2.31 x 10(-8), 1.54 x 10(-8), and 0.86 x 10(-8) M for Phe, Res, HQ, and Cat, respectively. The lifetime of the biomimetic sensor was 200 days at room temperature (at least 750 determinations). The catalytic properties of 1-CPE were characterized by chronoamperometry and were found to be in good agreement with Michaelis-Menten kinetics.

Solid phase extraction of lead and cadmium using solid sulfur as a new metal extractor prior to determination by flame atomic absorption spectrometry

A new method using a mini-column packed with sulfur as a new solid phase extractor has been developed for simultaneous preconcentration of lead and cadmium in water samples prior to flame atomic absorption spectrometric determinations. The effects of various parameters such as pH, flow rate of sample and eluent, type and concentration of eluent, sample volume, amount of adsorbent and interfering ions have been studied. The calibration graph was linear in the range of 10-300 and 1-20 ng mL(-1) for lead and cadmium, respectively. The limit of detection based on three times the standard deviation of the blank (3S(b)) was 3.2 and 0.2 ng mL(-1) (n=10) for lead and cadmium, respectively. A preconcentration factor of 250 was achieved in this method. The proposed procedure was applied to the determination of metal ions in tap, river and wastewater samples.

On-line molecularly imprinted solid-phase extraction for the selective spectrophotometric determination of nicotine in the urine of smokers

This work describes an on-line molecularly imprinted solid-phase extraction (MISPE) method for spectrophotometric determination of nicotine in urine samples of smokers. This method is based on manganese (VII) to manganese (VI) reduction in an alkaline medium, promoted by nicotine. Two wash solutions (1:4 (v/v) acetonitrile:sodium hydroxide--pH 11.4, and nitric acid--pH 2.5) were employed to circumvent interferences. Aqueous solutions containing nicotine plus different possible concomitants (cotinine, anabasine, norcotinine and caffeine) were tested individually. The analytical calibration curve was prepared in urine samples collected from non-smokers and spiked with nicotine standard from 1.1 to 60 micromol L(-1) (r(2)>0.998). The limit of quantification and the analytical frequency were 1.1 micromol L(-1) and 11 h(-1), respectively. The precision, evaluated using 3, 10 and 30 micromol L(-1) nicotine in urine, was 10, 10 and 4% (intra-day precision) and 12, 13 and 5% (inter-day precision), respectively. Accuracy was checked through high performance liquid chromatography and the results did not present significant differences at the 95% confidence level according to the Student's t-test.