Highly Selective Determination of Chrysoidine in Foods Through a Surface Molecularly Imprinted Sol–Gel Polymer Solid-Phase Extraction Coupled with HPLC

A highly selective determination method for chrysoidine, an industrial azoic dye banned in foods, was developed through a novel molecularly imprinted polymer (MIP) online solid-phase extraction coupled with high-performance liquid chromatography. The MIP was firstly synthesized by a surface molecular imprinting technique in combination with a sol–gel process and characterized by FT-IR and adsorption experiments. The MIP exhibited high selectivity and high adsorption capacity for chrysoidine and offered a fast kinetics for the adsorption and desorption of chrysoidine. A number of parameters, including the pH of loading solution, the sample loading flow rates, and eluting time of analyte, were carefully optimized to improve the extraction efficiency. Under the optimal experimental conditions, for a 50-mL sample solution, the enrichment factor was 279 and the detection limit (S/N?=?3) was 6 ng L^?1. The linear plots with r ²?>?0.99 were achieved over a range of 0.04–40 μg L^?1, and the peak area precision (relative standard deviation) for nine parallel determinations was below 6.32 %. This method was employed for quantitative determination of chrysoidine in oil bean curd, yellow croaker, and paprika with satisfactory recoveries (89.3–97.6 %).     

Magnetic Dummy Template Silica Sol–Gel Molecularly Imprinted Polymer Nanospheres as Magnetic Solid-Phase Extraction Material for the Selective and Sensitive Determination of Bisphenol A in Plastic Bottled Beverages

In this study, a core–shell magnetic dummy molecularly imprinted polymer (MDMIP) was prepared with a novel and simple method. The imprinting layer was synthesized directly on the surface of Fe₃O₄ by only one step, which avoided further modification on the exterior of magnetic core. 4,4′-Dihydroxybiphenyl (DDBP) was used as dummy template instead of bisphenol A (BPA) to eliminate the effect of template leakage on quantitative analysis. When used as solid-phase extraction sorbent, a rapid, sensitive, and accurate method for the simultaneous extraction, concentration, and determination of trace BPA in plastic bottled beverage samples by MDMIP-SPE coupled with high-performance liquid chromatography (HPLC) was developed. Advantages of such method may be counted as the mild working temperature during the synthesis, simplicity of extraction procedure, avoidance of leakage of template, time-saving, and high binding capacity and affinity. Several parameters affecting the extraction efficiency of the analytes including the sorbent mass, the pH of sample solution, the HAc percentage in the elute, and the desorption time were investigated. Under optimized conditions, the calibration graph was linear over the range of 11.4–4560 ng mL^?1 with the limit of detection of 0.083 ng L^?1. In addition, the higher enrichment factors (400-fold) and good recoveries (88.6–99.5%) with relative standard deviation (RSD) values less than 9.5% were achieved. Moreover, the developed extraction protocol simplified the process of traditional solid-phase extraction (SPE) provided the possibility for separation and enrichment of BPA from complicated food matrices.     

Combined Use of Liquid–Liquid Microextraction and Carbon Nanotube Reinforced Hollow Fiber Microporous Membrane Solid-Phase Microextraction for the Determination of Triazine Herbicides in Water and Milk Samples by High-Performance Liquid Chromatography

A simple, efficient and environmentally friendly method for the extraction and determination of five triazine herbicides in water and milk samples was developed by simultaneous liquid–liquid microextraction and carbon nanotube reinforced hollow fiber microporous membrane solid-phase microextraction coupled with high-performance liquid chromatography–diode array detection. The parameters that affect the extraction efficiencies, including the type and concentration of multi-walled carbon nanotube, type of membrane solvent and desorption solvent, the type and volume of the extraction solvent in sample solution, extraction time and temperature, the pH of sample solution, stirring rate, and ionic strength were investigated and optimized. Under the optimum conditions, the method shows a good linearity within a range of 0.5–200 ng mL⁻¹ for water samples and 1–200 ng mL⁻¹ for milk samples, with the correlation coefficients (r) varying from 0.9991 to 0.9998 and from 0.9989 to 0.9994, respectively. The limits of detection were in the range between 0.08 and 0.15 ng mL⁻¹ for water samples and 0.3 and 0.5 ng mL⁻¹ for milk samples, while the relative standard deviations varied from 4.6% to 6.9% and from 5.3% to 7.7%, respectively. The recoveries of the target analytes at spiking levels of 5.0 and 50.0 ng mL⁻¹ were in the range from 86.6% to 106.8% for water samples and from 81.3% to 97.4% for milk samples. The results demonstrated that the developed method was an efficient pretreatment and enrichment procedure for the determination of triazine pesticides in real water and milk samples.     

Solid-Phase Extraction of Florfenicol from Meat Samples by a Newly Synthesized Surface Molecularly Imprinted Sol–Gel Polymer

A new molecularly imprinted polymer (MIP) as a solid-phase sorbent for selective extraction of florfenicol (FF) was prepared by combination of the surface molecular imprinting technique with the sol–gel process. The FF-imprinted silica sorbent was prepared using FF as template, 3-aminopropyltriethoxysilane as functional monomer and tetraethoxysilicate as cross-linker on the silica gel support. The non-imprinted silica (NIP) was synthesized in the same way without addition of FF. The MIP was evaluated as a sorbent in column extraction approach for extraction of FF from aqueous solutions followed by spectrofluorometric determination. The influence of certain variables including the sample pH, the sample volume, the sample flow rate, the type of eluent, and its flow rate on the extraction efficiency of FF was assessed. The prepared FF-MIP silica sorbent showed higher adsorption capacity (64.9 mg g^?1) and significant selectivity than the corresponding NIP (11.5 mg g^?1). The FF-MIP-based solid phase extraction method was successfully applied to the separation and determination of FF from fish and chiken meat samples under the optimized extraction conditions.     

A Novel Cationic Surfactant-Assisted Switchable Solvent-Based Dispersive Liquid–Liquid Microextraction for Determination for Orange II in Food Samples

In this research, a new and green procedure based on the cationic surfactant-assisted switchable solvent-based dispersive liquid–liquid microextraction (CS-SS-DLLME) with UV-vis spectrophotometry was used for the extraction and determination of the Orange II dye in food samples. The main feature of the switchable solvent is the simple and reversible conversion of polarity protonated triethylammonium carbonate (P-TEA-C, ionic) to triethylamine (TEA, nonionic) by adding NaOH. This extraction method is based on hydrophilicity switchable solvent and ion pair effect of cationic surfactant. Simplicity, high-performance extraction, rapidity of the process, increase of stability, and reduction of the extractive phase volatility are other advantages of the proposed method. The parameters including the extraction and preconcentration of Orange II were studied and optimized. Under optimal conditions, the calibration curve was linear within the range of 2–450 μg/L and the detection limit was 0.9 μg/L and the relative standard deviation (RSD) for 80 μg/L of Orange II was 1.68%. This developed method was used successfully for the determination of Orange II in food samples.     

GC–MS Characterization of Volatile Compounds in Habanero Pepper (Capsicum chinense Jacq.) by Optimization of Headspace Solid-Phase Microextraction Conditions

Food Analytical Methods - The habanero pepper (Capsicum chinense Jacq.) is very aromatic and is the hottest pepper in the world. In this study, a headspace solid-phase microextraction/gas...     

Ultrasound-Assisted Extraction Followed by Solid-Phase Extraction Followed by Dispersive Liquid–Liquid Microextraction for the Sensitive Determination of Diazinon and Chlorpyrifos in Rice

Selectivity of solid-phase extraction (SPE) was combined with the concentration power of dispersive liquid–liquid microextraction (DLLME) to obtain a sensitive, low solvent consumption method for high-performance liquid chromatography determination of diazinon and chlorpyrifos in rice. In this method, rice samples were extracted by ultrasound-assisted extraction followed by SPE. Then, the SPE eluent was used as a disperser solvent in the next dispersive liquid-liquid microextraction step for further purification and enrichment of diazinon and chlorpyrifos. Under the optimal conditions, the linear range was from 5.0 to 250 μg kg^?1 for diazinon and from 2.5 to 250 μg kg^?1 for chlorpyrifos. Limits of detection of diazinon and chlorpyrifos were 1.5 and 0.7 μg kg^?1, respectively. Limits of quantitation of diazinon and chlorpyrifos were 5.5 and 3.0 μg kg^?1, respectively. The precisions and recoveries also were investigated by spiking 10 μg kg^?1 concentration in rice. The recoveries obtained were over 90 % with relative standard deviation (RSD%) below 9.0 %. The new approach was utilized to successfully detect trace amounts of diazinon and chlorpyrifos in different Iranian rice samples.     

A Novel Electrochemical Sensor Based on Graphene Oxide Decorated with Silver Nanoparticles–Molecular Imprinted Polymers for Determination of Sunset Yellow in Soft Drinks

In this study, a new imprinted electrochemical sensor for selectively detecting sunset yellow was developed based on glassy carbon electrode (GCE) modified by graphene oxide decorated with silver nanoparticles–molecular imprinted polymers (GO/AgNPs–MIPs). GO/AgNPs were firstly synthesized using self-assembly technology, and GO/AgNPs–MIPs were synthesized through surface imprinted technology by using GO/AgNPs as the substrate and sunset yellow as the template, respectively. The sensor was prepared by a drop-casting method. The synthetic materials were characterized by transmission electron microscope (TEM), Fourier transmission infrared spectra (FT-IR), and X-ray diffraction (XRD). The sensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The usage amount of GO/AgNPs–MIPs suspensions, solution pH, and accumulation time made an important difference in the process of detecting sunset yellow. Under optimal conditions, the peak current is linear to concentration of sunset yellow in the ranges of 0.1–0.6 and 0.6–12 μM, and the limit of detection was estimated to be 0.02 μM (S/N = 3). Finally, the proposed sensor was applied to detect sunset yellow in soft drinks with acceptable recovery, which demonstrated that the sensor could be used as a reliable and simple method for practical detection of sunset yellow.     

A Miniaturized Preconcentration Method Based on Dispersive Liquid–Liquid Microextraction for the Spectrophotometric Determination of Aziridine in Food Simulants

In this work a simple, rapid and sensitive method using dispersive liquid–liquid microextraction (DLLME) combined with UV–Vis spectrophotometry has been developed for the preconcentration and determination of trace amounts of aziridine in food simulants. The method is based on derivatization of aziridine with Folin's reagent (1,2-naphthoquione-4-sulphonic acid) and extraction of color product using DLLME technique. Some important parameters, such as reaction conditions, and type and volume of extraction solvent and disperser solvent were studied and optimized. Under optimum conditions, a linear calibration curve in the range of 2.0–350 ng mL^?1 of aziridine was obtained. Detection limit based on 3S_b was 1.0 ng mL^?1, and the relative standard deviation for 50 ng mL^?1 of aziridine was 2.49c (n?=?7). The proposed method was applied for the determination of aziridine in food simulants.     

Evaluation of Dispersive Liquid–Liquid Microextraction–HPLC–UV for Determination of Deoxynivalenol (DON) in Wheat Flour

A fast and simple method for the extraction of deoxynivalenol (DON) from wheat flour using dispersive liquid–liquid microextraction (DLLME) followed by high-performance liquid chromatography–UV detection has been developed and compared with immunoaffinity column cleanup (IAC) process. The influence of several important parameters on the extraction efficacy was studied. Under optimized conditions, a linear calibration curve was obtained in the range of 50–1,000 μg/L. Average recoveries of DON from spiked wheat samples at levels of 500 μg/kg for DLLME and IAC ranged from 72.9?±?1.6 and 85.5?±?3.1, respectively. A good correlation was found for spiked samples between DLLME and IAC methods. The limit of detection was 125 and 50 μg/kg for DLLME and IAC method, respectively. Advantages of DLLME method with respect to the IAC have been pointed out.     

Dispersive Liquid–Liquid Microextraction Followed by Magnetic Solid-Phase Extraction for Determination of Four Parabens in Beverage Samples by Ultra-performance Liquid Chromatography Tandem Mass Spectrometry

In this study, a two-step extraction technique was developed for extraction and preconcentration of parabens from beverage samples using ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) and magnetic solid-phase extraction (MSPE). In this IL-DLLME followed by MSPE method, ionic liquid (IL, 1-octyl-3-methylimidazolium hexafluorophosphate) formed hydrophobic microdroplets in beverage samples as an extractant of parabens; after the IL-DLLME process was completed, graphene modified Fe₃O₄ nanoparticles (Fe₃O₄@G) were placed to adsorb and isolate IL from the sample solution. After the supernatant was carefully moved, acetonitrile was added to elute the IL containing parabens from Fe₃O₄@G. The experimental variables affecting the extraction procedure have been systematically studied. Under optimal conditions, the detection limits were less than 1.53 ng/mL and the linear detection ranges were 2–500 ng/mL (R ² ≥ 0.998) for these analytes. The recoveries for spiked samples were 58.8–89.2% and satisfactory precision (RSD ≤ 4.8%) were obtained.     

Development of a Dispersive Liquid–Liquid Microextraction Method for the Determination of α-Tocopherol in Pigmented Wheat by High-Performance Liquid Chromatography

A dispersive liquid–liquid microextraction (DLLME) method coupled to high-performance liquid chromatography was developed for the analysis of α-tocopherol in grain samples. The DLLME parameters including the type and volume of extractants, the volume of disperser and the addition of salt were examined. The optimized DLLME procedure consisted in the formation of a cloudy solution promoted by the fast addition to the sample (5 mL of saponified sample solution diluted with 5 mL of water) of a mixture of carbon tetrachloride (extraction solvent, 80 μL) and ethanol (dispersive solvent, 200 μL) without the addition of salt, followed by shaking for 5 min and centrifuging for 3 min at 5,000 rpm. Intra- and inter-day repeatability expressed as % RSD were 3.5 and 7.6 %, respectively. The limit of detection and the limit of quantification were 1.9 and 6.3 μg?L^?1. The comparison of this method with the national standardized extraction method, supercritical carbon dioxide extraction, accelerated solvent extraction, and conventional heat-reflux extraction indicates that the DLLME was accurate (no significant differences at the 0.05 % probability level), high efficient, low organic solvent-consuming, and low cost. This procedure was successfully applied to 42 samples of 14 types of purple wheat, for which the content of α-tocopherol exhibited a significantly negative correlation with the pigment content measured by a spectrophotometer. The recovery rates ranged from 90.5 to 103.7 %.     

Ionic Liquid-Based Vortex-Assisted Liquid–Liquid Microextraction for Simultaneous Determination of Neonicotinoid Insecticides in Fruit Juice Samples

A simple, rapid, and effective method was developed for preconcentration of neonicotinoid insecticides including clothianidin, imidacloprid, acetamiprid, and thiacloprid in fruit juice samples. Room-temperature ionic liquids [C₄MIM][PF₆] can be used as green extractant phases in vortex-assisted liquid–liquid microextraction (VALLME), being compatible with high-performance liquid chromatographic systems. The effect of extraction parameters, including the addition of salt, volume of (C₄MIM)(PF₆), vortex time, and centrifugation time is identified as the key parameters of the method. Under the selected conditions, the high enrichment factors of 100 could be achieved with the limit of detection in the range of 0.25–0.30 ng mL^?1 and with the relative standard deviations of lower than 2.68 and 5.38 % for retention time and peak area, respectively. The proposed method was applied to the analysis of fruit juice samples, and the recoveries of the analytes ranged from 95 to 108 % and relative standard deviations were lower than 7 %. The developed method proposes advantages in reduction of the exposure danger to toxic organic solvents used in the conventional liquid–liquid extraction, simplicity of the extraction processes, rapidity, and sensitivity improvement.     

Optimisation of Glucose Biosensors Based on Sol–Gel Entrapment and Prussian Blue-Modified Screen-Printed Electrodes for Real Food Analysis

In this study, we report the construction of amperometric screen-printed glucose biosensors for food analysis by using two procedures for Prussian Blue (PB) deposition and different membranes for enzymatic immobilisation. The comparison between the screen-printed electrodes modified with PB by electrochemical and chemical deposition showed higher analytical performance (detection limit of 1 μM, linear range from 0.5 to 500 μM and a sensitivity of 823 μA mM^?1 cm^?2) when the latter was employed. Then, the immobilisation of glucose oxidase (GOD) by silica sol–gel and polyvinyl alcohol (PVA) hydrogel was performed on electrochemically modified PB electrodes. The electrochemical response of two glucose biosensors was evaluated by flow injection analysis. Biosensors constructed by silica sol–gel entrapment showed a wider linear range (0.005–1 mM) and a detection limit (0.02 mM) that was 10-fold lower than using entrapped GOD in PVA. The selected glucose biosensor showed negligible interference from ascorbic acid when the Nafion membrane was used to cover the PB-modified electrode surface. Additionally, it exhibited an operating lifetime of 8 h under continuous glucose injections ranging from 0.01 to 2 mM. Finally, the biosensor was applied for specific determination of glucose in red and white wines, juices and dried fruit.     

Dispersive Solid-Phase Extraction Clean-up Combined with Dispersive Liquid�CLiquid Microextraction for the Determination of Neonicotinoid Insecticides in Vegetable Samples by High-Performance Liquid Chromatography

Dispersive solid-phase extraction (DSPE) clean-up combined with dispersive liquid–liquid microextraction (DLLME) has been developed as a new approach for the extraction of neonicotinoid insecticides in vegetable samples prior to high-performance liquid chromatography with diode array detection. In the DSPE–DLLME method, neonicotinoid insecticides were first extracted with acetonitrile from vegetable samples, followed by clean-up by a DSPE with primary secondary amine and multi-walled carbonnanotubes as sorbents. A 2.5-mL aliquot of the resulting extract was then added into a centrifuge tube containing 10 mL of water, 0.8 g NaCl, and 200-μL chloroform (as the extraction solvent) for DLLME procedure. Under the optimum conditions, the enrichment factors for the compounds were in the range between 110 and 243. The linearity of the method was in the range from 5.0 to 300 ng g⁻¹ with the correlation coefficients (r) ranging from 0.9989 to 0.9998. The detection limits of the method were 0.5–1.0 ng g⁻¹. The repeatability of the method expressed as the relative standard deviations by five parallel experiments at the concentration levels of 10 and 50 ng g⁻¹ each of the neonicotinoid insecticides in tomato or cucumber samples varied from 3.6% to 5.8%. The developed method has been successfully applied for the analysis of target neonicotinoid insecticides (acetamiprid, imidacloprid, thiacloprid, and thiamethoxam) in tomato and cucumber samples. The recoveries of the method for the target neonicotinoid insecticides from the vegetable samples at spiking levels of 10.0 and 50.0 ng g⁻¹ were in the range between 84.6% and 97.5% (n = 5).     

On-line Solid-Phase Extraction Coupled to Liquid Chromatography–Ion Trap Tandem Mass Spectrometry for Determination of Penicillins in Catfish

A highly selective method was developed for the simultaneous determination of eight penicillins in catfish using automated on-line solid-phase extraction coupled to liquid chromatography–tandem mass spectrometry (XLC–MS/MS). The type of cartridge, equilibration sample volume, volume of solvent to carry the sample into the cartridge, and elution times were studied in order to optimize the XLC operating conditions. MS/MS conditions were also adjusted for better peak resolution. The present method was validated in agreement with the criteria of Commission Decision 2002/657/EC, showing a linear range from 2 to 350 μg kg⁻¹ and regression coefficient higher than 0.995 for the studied penicillins. Decision limits, calculated in the case of substances with no permitted limit, were lower than 0.6 μg kg⁻¹, and detection capability values were lower than 2.0 μg kg⁻¹. Samples spiked at 2.0, 10.0, and 50.0 μg kg⁻¹ showed high recovery (72–92%) and precision values lower than 20% except for amoxicillin. The present method was also applied for the analysis of penicillins in 30 catfish samples bought in local markets.     

Determination of Sulfite in Water and Dried Fruit Samples by Dispersive Liquid–Liquid Microextraction Combined with UV–Vis Fiber Optic Linear Array Spectrophotometry

A simple and rapid dispersive liquid?Cliquid microextraction (DLLME) method was applied to preconcentrate sulfite ions from aqueous samples as a prior step to its determination by fiber optic-linear array detection spectrophotometry. The procedure is based on the color reaction of sulfite with o-phthaldialdehyde (OPA) in the presence of ammonia to form isoindole and extraction of the formed isoindole derivative using the DLLME technique. The conditions for the microextraction performance were investigated and optimized. The calibration graph was linear in the range of 2?C100???g?L^?1with a detection limit of 0.2???g?L^?1. The relative standard deviation for five replicate measurements of 10 and 50???g?L^?1of sulfite were 2.8 and 2.0?%, respectively. Under the optimized conditions, the enrichment factor of ~133 was obtained from a sample volume of 10?mL. The proposed method was successfully applied to the sulfite determination in drinking water and in food samples.     

Ionic Liquid-Based Dispersive Liquid–Liquid Microextraction Following High-Performance Liquid Chromatography for the Determination of Fungicides in Fruit Juices

This paper described an ionic liquid-based dispersive liquid–liquid microextraction (IL-DLLME) combined with high-performance liquid chromatography (HPLC) method to determine fungicides in fruit juices. In this method, 1-hexyl-3-methyli-midazolium hexafluorophosphate (HMIMPF₆) was used as extraction solvent, which dispersed into the fruit juices under vigorously shaking with the vortex. The effects of experimental parameters, such as extraction solvent volume, disperser solvent and its volume, vortex time, centrifugation time, sample pH, on the extraction efficiency were investigated. Under the optimum conditions, the linear correlation coefficients ranged from 0.9902 to 0.9979 for concentration levels of 0.02–2 mg l^?1, the extraction recoveries were ranged 66.2–92.9 % except pyrimethanil (39.5–44.6 %), The relative standard deviations (RSDs; n?=?6) ranged from 2.2 % to 11.6 %, and the limits of detection (LODs) for the fungicides were between 3.1 and 10.2 μg l^?1. Two real samples including apple and grape juices, spiked at two concentration levels were analyzed and yielded recoveries ranging from 71.3–93.1 % and 65.4–87.7 %, respectively.     

Dispersive Liquid–Liquid Microextraction Combined With Micellar Electrokinetic Chromatography for the Determination of Some Photoinitiators in Fruit Juice

A fast and simple technique composed of dispersive liquid–liquid microextraction (DLLME) and micellar electrokinetic chromatography (MEKC) with diode array detector (DAD) was developed for the determination of multi-photoinitiators in fruit juice. Seven photoinitiators were separated in MEKC using a 25 mM borate buffer of pH 8.0, containing 24 mM sodium dodecyl sulfate (SDS), 10 mM β-cyclodextrin (β-CD), and 12.5 % acetonitrile (v/v). A CD-modified MEKC made this method more suitable for the determination of isopropylthioxanthone (ITX) isomers including 2-IXT and 4-ITX than the recently prescribed methods. A DLLME procedure was used as an offline preconcentration strategy. The satisfactory recoveries obtained by DLLME spiked at two spiked levels ranged from 85.6 to 124.7 % with relative standard deviations (RSDs) below 14 %. The limits of quantification (LOQs) ranged from 2.1 to 6.0 μg kg^?1.     

Vortex-Assisted Liquid–Liquid Microextraction Combined with HPLC for the Simultaneous Determination of Five Phthalate Esters in Liquor Samples

A vortex-assisted liquid–liquid microextraction (VALLME) method using hexanoic acid as extractant followed by high-performance liquid chromatography–diode array detection was developed for the extraction and determination of five phthalate esters (PAEs) including bis-methylglycol ester (DMEP), benzyl butyl phthalate (BBP), dicyclohexyl phthalate (DCHP), di-n-butyl phthalate (DBP), and di-n-octyl phthalate (DNOP) from liquor samples. In this method, hexanoic acid was employed as extraction solvent, because its density is lower than water. And vortex mixing was utilized as a mild emulsification procedure to reduce emulsification time and improve the effect of extraction. Under the studied conditions, five phthalate esters were successfully separated within 20 min and the limits of detection were 2.3 ng mL^?1 for DMEP, 1.1 ng mL^?1 for BBP, 1.9 ng mL^?1 for DCHP, 1.2 ng mL^?1 for DBP, and 1.5 ng mL^?1 for DNOP, respectively. Recoveries of the PAEs spiked into liquor samples were ranged from 89 to 93 %. The precisions of the proposed method were varied from 1.6 to 2.6 % (RSD). The VALLME method has been proved to have the potential to be applied to the preconcentration of the target analytes. Moreover, the method is simple, high sensitivity, consumes much less solvent than traditional methods and environmental friendly.