Electrochemical detection of methyl parathion using calix[6]arene/bismuth ferrite/multiwall carbon nanotube-modified fluorine-doped tin oxide electrode.

A highly sensitive electrochemical sensor using a calix[6]arene/bismuth ferrite/multiwall carbon nanotube-modified fluorine-doped tin oxide electrode (CA6/BFO/MWCNTs/FTO) was fabricated for the detection of methyl parathion. The MWCNTs, BFO, and CA6 were consecutively cast onto the FTO electrode surface to enhance the surface area, electron transfer, and selectivity of sensors. The electrochemical behavior of CA6/BFO/MWCNTs/FTO was studied via cyclic voltammetry and electrochemical impedance spectroscopy. MP was detected via cyclic voltammetry in a phosphate buffer solution at pH 7.0. The working principle of the sensor involves a linear decrease in the anodic peak current of BFO with increasing MP concentration. The linear working ranges are 0.005-0.05 nM and 0.07-1.5 nM. The CA6/BFO/MWCNTs/FTO sensor provides a low detection limit (S/N = 3) of 5 pM and a high electrochemical sensitivity of 1.23 A µM-1 cm-2. The fabricated sensor was successfully applied to assess the presence and amount of MP in vegetables and fruits (recoveries of 82.0-106.8%), with results comparable to high-performance liquid chromatography.

An In Situ Formation of Ionic Liquid for Enrichment of Triazole Fungicides in Food Applications Followed by HPLC Determination.

An in situ formation of ionic liquid was used for preconcentration of four triazole fungicides in food samples. The microextraction method was used for the first time in the literature for preconcentration of triazole fungicides. In the developed method, tributylhexadecylphosphonium bromide ([P44412]Br) and potassium hexafluorophosphate (KPF6) were used for the formation of hydrophobic ionic liquid. After centrifugation, the fine microdroplets were produced in one step, providing the extraction step in a quick and environmentally friendly manner. The functional group of the hydrophobic ionic liquid was investigated using FT-IR. Various extraction parameters were studied and optimized. In the extraction method, 0.01 g of [P44412]Br and 0.01 g of KPF6, centrifugation at 4500 rpm for 10 min were used. The optimized technique provided a good linear range (90-1000 µg L-1) and high extraction recovery, with a low limit of detection (30-50 µg L-1). Methods for the proposed in situ formation of ionic liquid were successfully applied to honey, fruit juice, and egg matrices. The recoveries were obtained in a satisfactory range of 62-112%. The results confirmed the suitability of the proposed microextraction method for selective extraction and quantification of triazole fungicides.

Simultaneous Preconcentration of Triazole Fungicide Residues Using In-Situ Coacervative Extraction Based on a Double-Solvent Supramolecular System Prior to High Performance Liquid Chromatographic Analysis.

An in situ coacervative extraction (IS-CAE) based on a double-solvent supramolecular system coupled to liquid-liquid microextraction is investigated for extraction and enrichment of triazole fungicides. The formation of a double-solvent supramolecular system was generated by in situ formation and used as an extraction solvent for the coacervative extraction method. No disperser solvent was required. This new double-solvent supramolecular system has a higher extraction ability than any of its components alone. The different factors that could affect the extraction capability were studied and optimized, including the type of double extractant and its volume, salt addition, vortex time, and centrifugation time. Under optimum extraction conditions, this method provides high enrichment factors (EFs) of 73-318 with low limits of detection (LODs) of 0.3-1 µg L-1 and limits of quantitation (LOQs) of 1-3 µg L-1. In addition, the proposed method was prosperously applied for the determination of triazole fungicides in water, fruit juice, and soy milk samples.

An electrochemical sensor for voltammetric detection of ciprofloxacin using a glassy carbon electrode modified with activated carbon, gold nanoparticles and supramolecular solvent.

A highly sensitive and novel electrochemical sensor for ciprofloxacin (CIP) has been developed using gold nanoparticles deposited with waste coffee ground activated carbon on glassy carbon electrode (AuNPs/AC/GCE) and combined with supramolecular solvent (SUPRAS). The fabricated AuNPs/AC/GCE displayed good electrocatalytic activity for AuNPs. The addition of SUPRAS, prepared from cationic surfactants namely didodecyldimethylammonium bromide (DDAB) and dodecyltrimethylammonium bromide (DTAB), increased the electrochemical response of AuNPs. The detection of CIP was based on the decrease of the cathodic current of AuNPs. The electrochemical behavior of the modified electrode was investigated using cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. Under optimum conditions, the calibration plot of CIP exhibited a linear response in the range 0.5-25 nM with a detection limit of 0.20 nM. The fabricated electrochemical sensor was successfully applied to determine CIP in milk samples with achieved recoveries of 78.6-110.2% and relative standard deviations of <8.4%. The developed method was also applied to the analysis of pharmaceutical formulation and the results were compared with high-performance liquid chromatography.Graphical abstract.

In-Situ Formation of Modified Nickel-Zinc-Layered Double Hydroxide Followed by HPLC Determination of Neonicotinoid Insecticide Residues.

A single-step preconcentration procedure using the in-situ formation of modified nickel-zinc-layered double hydroxides (LDHs) prior to high-performance liquid chromatography (HPLC) is investigated for the determination of neonicotinoid insecticide residues in honey samples. The LDHs could be prepared by the sequential addition of sodium hydroxide, sodium dodecyl sulfate, nickel nitrate 6-hydrate and zinc nitrate 6-hydrate, which were added to the sample solution. The co-precipitate phase and phase separation were obtained by centrifugation, and then the precipitate phase was dissolved in formic acid (concentrate) prior to HPLC analysis. Various analytical parameters affecting extraction efficiency were studied, and the characterization of the LDHs phase was performed using Fourier-transformed infrared spectroscopy and scanning electron microscopy. Under optimum conditions, the limit of detection of the studied neonicotinoids, in real samples, were 30 µg L-1, for all analytes, lower than the maximum residue limits established by the European Union (EU). The developed method provided high enrichment, by a factor of 35. The proposed method was utilized to determine the target insecticides in honey samples, and acceptable recoveries were obtained.

A Simple in Syringe Low Density Solvent-Dispersive Liquid Liquid Microextraction for Enrichment of Some Metal Ions Prior to Their Determination by High Performance Liquid Chromatography in Food Samples.

A simple and highly sensitive method is developed for the simultaneous determination of Ni2+, Cr2O72-, Co2+, and Hg2+ by using in syringe low density solvent-dispersive liquid liquid microextraction (ISLD-DLLME), followed by high performance liquid chromatography with a UV detector. The four metal ions were derivatized with pyrrolidine dithiocarbamate (PDC) based on complexation before their enrichment by ISLD-DLLME in which 1-octanol and methanol were used as the extraction solvent and the dispersive solvent, respectively. The extraction was performed in a commercially available syringe under vortex agitation. Phase separation was achieved without centrifugation, and the extraction phase was easily collected by moving the syringe plunger. Parameters affecting the extraction efficiency were studied and optimized. Under the optimum conditions, the four metal-PDC complexes were detected within 18 min, and ISLD-DLLME could increase the detection sensitivity in the range of 64-230 times compared to the direct HPLC analysis. The obtained limits of detection (LODs) were found to be in the range of 0.011-2.0 µg L-1. The applicability of the method is demonstrated for freshwater fish, shrimp, and shellfish samples. In addition, the results are in good agreement with those obtained by inductively-coupled plasma-optical emission spectrometry (ICP-OES).

An Eco-Friendly Hydrophobic Deep Eutectic Solvent-Based Dispersive Liquid-Liquid Microextraction for the Determination of Neonicotinoid Insecticide Residues in Water, Soil and Egg Yolk Samples.

A green, simple and sensitive hydrophobic DES-based dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography (HPLC) was developed for the analysis of neonicotinoid insecticide residues in various samples. A hydrophobic deep eutectic solvent (DES) was synthesized using decanoic acid as a hydrogen bond donor and tetrabutylammonium bromide (TBABr) as a hydrogen bond-acceptor. DESs were synthesized and characterized by Fourier transform-infrared (FTIR) spectroscopy. Two disperser solvents were substituted with surfactants and acetonitrile, which could afford more effective emulsification and make the extraction relatively greener. The hydrophobic DES extraction phase occurred 10 min after centrifugation, being easy to be collected for analysis. Several parameters were investigated and optimized. Under the optimum condition, the calibration curve of this method was linear in the range of 0.003-1.0-µg·mL-1, with a correlation coefficient (R2) higher than 0.99 and a good repeatability, with the relative standard deviations (RSDs) were less than 5.00%. The limits of detection were in the range of 0.001-0.003 µg·mL-1; the limits of quantitation were in the range of 0.003-0.009 µg·mL·mL-1. Finally, the presented method was implemented to determine the neonicotinoid insecticide residues in water, soil, egg yolk samples and acceptable recoveries were obtained.

Supramolecular Electrochemical Sensor for Dopamine Detection Based on Self-Assembled Mixed Surfactants on Gold Nanoparticles Deposited Graphene Oxide.

A new supramolecular electrochemical sensor for highly sensitive detection of dopamine (DA) was fabricated based on supramolecular assemblies of mixed two surfactants, tetra-butylammonium bromide (TBABr) and sodium dodecyl sulphate (SDS), on the electrodeposition of gold nanoparticles on graphene oxide modified on glassy carbon electrode (AuNPs/GO/GCE). Self-assembled mixed surfactants (TBABr/SDS) were added into the solution to increase the sensitivity for the detection of DA. All electrodes were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The supramolecular electrochemical sensor (TBABr/SDS⋅⋅⋅AuNPs/GO/GCE) showed excellent electrocatalytic activity toward the oxidation of DA. Under the optimum conditions, the concentration of DA was obtained in the range from 0.02 µM to 1.00 µM, with a detection limit of 0.01 µM (3s/b). The results displayed that TBABr/SDS⋅⋅⋅AuNPs/GO/GCE exhibited excellent performance, good sensitivity, and reproducibility. In addition, the proposed supramolecular electrochemical sensor was successfully applied to determine DA in human serum samples with satisfactory recoveries (97.26% to 104.21%).

ß-Cyclodextrin Assisted Liquid-Liquid Microextraction Based on Solidification of the Floating Organic Droplets Method for Determination of Neonicotinoid Residues.

An efficient and environment-friendly microextraction method, namely, ß-cyclodextrin assisted liquid-liquid microextraction, based on solidification of the floating organic droplets method coupled with HPLC is investigated for the sensitive determination of trace neonicotinoid pesticide residues. In this method, ß-cyclodextrin is used as a disperser solvent, while 1-octanol is selected as an extraction solvent. ß-cyclodextrins was found to decrease interfacial tension and increase the contact area between the organic and water phases with the help of centrifugation. A cloudy solution was rapidly formed and then centrifuged to complete phase separation. Various key parameters influencing extraction efficiency were systematically investigated and optimized; they include salt addition, concentration of ß-cyclodextrin, and volume of extraction solvent (1-octanol). Under optimum conditions, good linearity was obtained with coefficient for determination (R2) greater than 0.99. A low limit of detection, high enrichment factor, and good recovery (83 - 132) were achieved. This proves that the proposed method can be applied to determine trace neonicotinoid pesticide residues in natural surface water samples.

Silver-doped CdS quantum dots incorporated into chitosan-coated cellulose as a colorimetric paper test stripe for mercury.

Silver-doped CdS quantum dots capped with mercaptoacetic acid were incorporated into a chitosan-coated filter paper to fabricate a colorimetric test stripe for mercury. Chitosan assisted in the stabilization of CdSAg QDs on cellulose and enhanced the analyte diffusion in the test stripe. Hg(II) ions were captured by mercaptoacetic acid on CdSAg, resulting in a visualized color change from yellow to deep brown. For enhanced sensitivity and quantitation with good reproducibility, the color intensity was recorded, transmitted to a smartphone camera and computed by the ImageJ software to provide a digital readout. The assay was rapid, simple, and selective for mercury as several potential interfering species provoked no signal response. The applicability of the sensing approach was demonstrated for the analysis of spiked Hg(II) ions in cosmetic cream with a detection limit of 124 µM. Graphical abstract Schematic of a colorimetric test stripe consisting of silver-doped CdS quantum dots coated withmercaptoacetic acid and embedded into a chitosan matrix on paper. It enables mercury(II) to be visuallyquantified even in complex matrices such as cosmetics.

Ultrasonically Modified Amended-Cloud Point Extraction for Simultaneous Pre-Concentration of Neonicotinoid Insecticide Residues.

An effective pre-concentration method, namely amended-cloud point extraction (CPE), has been developed for the extraction and pre-concentration of neonicotinoid insecticide residues. The studied analytes including clothianidin, imidacloprid, acetamiprid, thiamethoxam and thiacloprid were chosen as a model compound. The amended-CPE procedure included two cloud point processes. Triton™ X-114 was used to extract neonicotinoid residues into the surfactant-rich phase and then the analytes were transferred into an alkaline solution with the help of ultrasound energy. The extracts were then analyzed by high-performance liquid chromatography (HPLC) coupled with a monolithic column. Several factors influencing the extraction efficiency were studied such as kind and concentration of surfactant, type and content of salts, kind and concentration of back extraction agent, and incubation temperature and time. Enrichment factors (EFs) were found in the range of 20⁻333 folds. The limits of detection of the studied neonicotinoids were in the range of 0.0003⁻0.002 µg mL−1 which are below the maximum residue limits (MRLs) established by the European Union (EU). Good repeatability was obtained with relative standard deviations lower than 1.92% and 4.54% for retention time (tR) and peak area, respectively. The developed extraction method was successfully applied for the analysis of water samples. No detectable residues of neonicotinoids in the studied samples were found.

Preconcentration of Trace Neonicotinoid Insecticide Residues Using Vortex-Assisted Dispersive Micro Solid-Phase Extraction with Montmorillonite as an Efficient Sorbent.

In this work, we investigated montmorillonite for adsorption of neonicotinoid insecticides in vortex-assisted dispersive micro-solid phase extraction (VA-d-µ-SPE). High-performance liquid chromatography with photodiode array detection was used for quantification and determination of neonicotinoid insecticide residues, including thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid. In this method, the solid sorbent was dispersed into the aqueous sample solution and vortex agitation was performed to accelerate the extraction process. Finally, the solution was filtered from the solid sorbent with a membrane filter. The parameters affecting the extraction efficiency of the proposed method were optimized, such as amount of sorbent, sample volume, salt addition, type and volume of extraction solvent, and vortex time. The adsorbing results show that montmorillonite could be reused at least 4 times and be used as an effective adsorbent for rapid extraction/preconcentration of neonicotinoid insecticide residues. Under optimum conditions, linear dynamic ranges were achieved between 0.5 and 1000 ng mL-1 with a correlation of determination (R²) greater than 0.99. Limit of detection (LOD) ranged from 0.005 to 0.065 ng mL-1, while limit of quantification (LOQ) ranged from 0.008 to 0.263 ng mL-1. The enrichment factor (EF) ranged from 8 to 176-fold. The results demonstrated that the proposed method not only provided a more simple and sensitive method, but also can be used as a powerful alternative method for the simultaneous determination of insecticide residues in natural surface water and fruit juice samples.

Ionic Liquid-Assisted Liquid-Liquid Microextraction based on the Solidification of Floating Organic Droplet in Sample Preparation for Simultaneous Determination of Herbicide Residues in Fruits.

An ionic liquid-assisted liquid-liquid microextraction based on the solidification of floating organic droplet (ILSFODLLME) was investigated for analysis of four herbicide residues (i.e. simazine, atrazine, propazine, and linuron) by high performance liquid chromatography. For ILSFOD-LLME, the optimal extraction conditions were 5% w/v Na2SO4, 30 µL [C4MIM][PF6]RTIL, 100 µL of 1-octanol, ultrasonication time 30 s and centrifugation at 5000 rpm for 5 min. Under the optimal conditions, linearity was obtained within the range of 0.1-1000 µg kg-1, with the correlation coefficients greater than 0.999. The high enrichment factors of the target analytes were in the range of 64.5-139.9 and low limit of detection could be obtained. A modified QuEChERS was applied for fruit sample preparation before analysis. Matrix effects were also investigated using matrix matched standards for construction of the calibration graph. The proposed method has been successfully applied for extraction and preconcentration of herbicide residues in fruit samples, and good recoveries in the range of 87.32% to 99.93% were obtained.

Methyl Salicylate-Based Vortex-Assisted Surfactant-Enhanced Emulsification Microextraction and HPLC for Determination of Fungicides in Honey Samples.

Methyl salicylate based vortex-assisted surfactant-enhanced emulsification microextraction (MeSA-VASEME) has been developed and applied for rapid preconcentration of fungicides (i.e., carbendazim, thiabendazole, and fluberidazole) in honey samples followed by high performance liquid chromatographic analysis. MeSA was used as an extraction solvent, while surfactant was used to enhance the extraction performance under the dispersion by vortex agitation. The optimum MeSA-VASEME conditions were 100 µL MeSA, 2.0 mmol L‒1 sodium dodecyl sulfate, and vortex agitation at 1200 rpm for 90 s. Preconcentration factors were obtained in the range of 32-40. The limit of detection in the studied honey samples was 0.5 µg L‒1. The recovery of the spiked target fungicides at 20, 50, and 100 µg L‒1 were 81.5-116.8 % with the relative standard deviation below 11%. The proposed method is simple, sensitive, less organic solvent consuming, inexpensive, and a rapid procedure for the residue analysis of fungicides in honey samples.

A New Approach for Removing Anionic Organic Dyes from Wastewater Based on Electrostatically Driven Assembly.

A conceptually new approach for an efficient removal of anionic organic dyes from wastewater using layered double hydroxides (LDHs) through their formation is presented. Acid yellow 25 (AY25) was used as anionic organic dye model molecules. As a result of the electrostatic induction, the removal mechanism involved a concurrent incorporation of AY25 molecules into the interlayer of LDHs during their structural arrangement, where Mg(2+) and Al(3+) ions were utilized to construct the base of LDHs in an alkaline solution. It was found that the molar stoichiometry of all precursors was a key factor affecting the removal efficiency. Within 5 min removal time, this method still maintained high removal efficiency of over 97% and provided a removal capacity of ∼186 mg g(-1), comparable to that of other LDH-based methods. Also, almost complete dye recovery was simply achieved by anionic exchange with common anions (Cl(-), NO3(-), and CO3(2-)). Additionally, the present technique is straightforward, cost-effective, and environmentally friendly since it avoids the synthesis step of sorbents, thus significantly saving time, chemicals, and energy. Hence, this strategy not only exhibits the alternative exploitation of LDHs, but also provides new insights into the removal of contaminants from wastewater.

Interface-free two-dimensional heart-cutting capillary electrophoresis for the separation and stacking of anionic and neutral analytes.

Interface-free two-dimensional heart-cutting capillary electrophoresis for two different classes of analytes (anionic and neutral) in a single capillary is presented. Simultaneous sample stacking and orthogonal separation were demonstrated. The anionic species were first analyzed by capillary zone electrophoresis in the first dimension. Then, the neutral compounds were separated in the second dimension by micellar electrokinetic chromatography using the common anionic surfactant sodium dodecyl sulfate. The first and second dimensions occurred automatically without changing the electrolyte and without polarity switching. Artificial mixtures (five anions and four neutral compounds) were successfully analyzed with sensitivity enhancement factors from 7 to 28. The orthogonal separation was complete within 8 min. Some analytical features and application to a spiked real river water sample were also studied.

Preparation of Inulin Powder from Jerusalem Artichoke (Helianthus tuberosus L.) Tuber.

The complete procedure for the production of inulin powder from Jerusalem artichoke tubers (JAT) was investigated. The procedure consists of isolation of inulin from JAT, elimination of color from the inulin extract and solidification. Washed tubers were first sliced, dried in a 60 °C oven for 10 h and then milled and sieved into a powder. Inulin was isolated from the JAT powder by hot water extraction using an accelerated solvent extractor (ASE). The effects of temperature and time for the extraction were investigated. The highest extraction efficiency was obtained at the extraction temperature of 80 °C for 20 min. The color of the extract was eliminated using ion exchange process with diethylaminoethyl cellulose as the sorbent. The inulin powder was subsequently obtained by freeze drying. Inulin content and inulin profiles were monitored to evaluate the efficiencies of the complete procedure. The inulin content was indirectly determined by spectrophotometry from free and total fructose measurements using potassium iodide. The inulin profile was monitored using high performance anion exchange chromatography equipped with integrated pulse amperometric detection (HPAEC-PAD). The proposed method provided the inulin production yield of 92.5%. The present procedure is fast, simple and effective for production of inulin powder from JAT. In addition, infrared spectra and some physico-chemical properties of the obtained inulin powder were determined and compared with the standard inulin.

Stacking and separation of neutral and cationic analytes in interface-free two-dimensional heart-cutting capillary electrophoresis.

Interface-free two-dimensional heart-cutting capillary electrophoresis is typically used to purify/concentrate and separate a single target fraction. Here, we demonstrate the simultaneous stacking and orthogonal separation of target fractions that belong to two different classes of compounds. The cationic species were first analyzed by capillary zone electrophoresis using an electrolyte of low pH in a fused-silica capillary. The neutrals that remained inside the capillary after the first dimension analysis were then separated by micellar electrokinetic chromatography using sodium dodecyl sulfate micelles that were electrophoretically introduced into the capillary. The suppression of electro-osmotic flow using low pH was essential in shifting the separation selectivity from electrophoresis to electrokinetic chromatography. Two approaches to stacking based on the solubility of the species present were developed. Stacking was achieved during the first dimension analysis via sweeping and/or analyte focusing by micelle collapse. Two artificial mixtures (eight cationic drugs/five neutral steroids, and three quaternary ammonium/three neutral organophosphate pesticides) were successfully analyzed with sensitivity enhancement factors from 15 to 100. Some analytical parameters and application to a spiked real water sample were also studied.

Anionic microemulsion to solvent stacking for on-line sample concentration of cationic analytes in capillary electrophoresis.

The common SDS microemulsion (i.e. 3.3% SDS, 0.8% octane, and 6.6% butanol) and organic solvents were investigated for the stacking of cationic drugs in capillary zone electrophoresis using a low pH separation electrolyte. The sample was prepared in the acidic microemulsion and a high percentage of organic solvent was included in the electrolyte at anodic end of capillary. The stacking mechanism was similar to micelle to solvent stacking where the micelles were replaced by the microemulsion for the transport of analytes to the organic solvent rich boundary. This boundary is found between the microemulsion and anodic electrolyte. The effective electrophoretic mobility of the cations reversed from the direction of the anode in the microemulsion to the cathode in the boundary. Microemulsion to solvent stacking was successfully achieved with 40% ACN in the anodic electrolyte and hydrodynamic sample injection of 21 s at 1000 mbar (equivalent to 30% of the effective length). The sensitivity enhancement factors in terms of peak height and corrected peak area were 15 to 35 and 21 to 47, respectively. The linearity R(2) in terms of corrected peak area were >0.999. Interday precisions (%RSD, n = 6) were 3.3-4.0% for corrected peak area and 2.0-3.0% for migration time. Application to spiked real sample is also presented.

Alternative solvent-based methyl benzoate vortex-assisted dispersive liquid-liquid microextraction for the high-performance liquid chromatographic determination of benzimidazole fungicides in environmental water samples.

Vortex-assisted dispersive liquid-liquid microextraction using methyl benzoate as an alternative extraction solvent for extracting and preconcentrating three benzimidazole fungicides (i.e., carbendazim, thiabendazole, and fluberidazole) in environmental water samples before high-performance liquid chromatographic analysis has been developed. The selected microextraction conditions were 250 µL of methyl benzoate containing 300 µL of ethanol, 1.0% w/v sodium acetate, and vortex agitation speed of 2100 rpm for 30 s. Under optimum conditions, preconcentration factors were 14.5-39.0 for the target fungicides. Limits of detection were obtained in the range of 0.01-0.05 µg/L. The proposed method was then applied to surface water samples and the recovery evaluations at three spiked concentration levels of 5, 30, and 50 µg/L were obtained in the range of 77.4-110.9% with the relative standard deviation <7.4%. The present method was simple, rapid, low cost, sensitive, environmentally friendly, and suitable for the trace analysis of the studied fungicides in environmental water samples.