Preparation and Evaluation of Histamine Imprinted Polymer as a Selective Sorbent in Molecularly Imprinted Solid-Phase Extraction Coupled with High Performance Liquid Chromatography Analysis in Canned Fish

A series of molecularly imprinted polymers (MIPs) were prepared against histamine. Different template/monomer ratios were applied to optimize the imprinting condition. Methacrylic acid (MAA) as a functional monomer and Chloroform as a solvent were applied in polymerization process. The binding properties of MIPs were studied in comparison with a blank non-imprinted polymer. The optimized polymer, with a histamine/MAA ratio of 1/4, was selected as a sorbent in molecularly imprinted solid-phase extraction (MISPE) of histamine from canned fish. Scatchard analysis of MIP-histamine interactions revealed two types of binding sites for MIP: high affinity (K_D?=?11.11 μM) and low affinity (K_D?=?333.3 μM). The MISPE procedure was calibrated and a recovery of 76.5–97.6 % was obtained. The intra-and inter-day precision values were less than 5.70 % and 10.1 %, respectively. The selectivity of MISPE for histamine was also studied in comparison with some other structurally similar amines, which could be simultaneously present in canned fish. The performance of the imprinted polymer was examined and the results indicated that its good selectivity and affinity for histamine was very promising. Therefore, the proposed calibrated method could be applied in selective extraction and analysis of histamine in canned fish.     

Rapid determination of Alternaria mycotoxins in tomato samples by pressurised liquid extraction coupled to liquid chromatography with fluorescence detection

ABSTRACT

A sensitive and reliable method using pressurised liquid extraction (PLE) followed by molecularly imprinted solid phase extraction (MISPE) and high performance liquid chromatography with fluorescence detection (HPLC–FLD) has been developed for the analysis of alternariol (AOH) and alternariol monomethyl ether (AME) in tomato samples. Influence of several extraction parameters that affect PLE efficiency were evaluated for the simultaneous extraction of both mycotoxins in the selected samples. AOH and AME were optimally extracted using MeOH/water (25:75, v/v) at 70°C as solvent, a pressure of 1000 psi and a single extraction cycle. The resulting PLE extracts were pre-concentrated by molecularly imprinted solid phase extraction (MISPE) cartridges followed of analysis by HPLC with fluorescence detection (λ_exc = 258, λ_em = 440 nm). The proposed method was applied to the analysis of AOH and AME in fortified tomato samples (20–72 µg· kg–1) with recoveries of 84–97% (RSD < 8%, n = 6) for AOH and 67–91% (RSD < 13%, n = 6) for AME. The detection limit for AOH and AME were 7 and 15 µg· kg^–1, respectively. The ensuing PLE–MISPE–HPLC–FLD method was validated for the analysis of both mycotoxins in tomato samples in accordance with European Commission Decision 2002/657/EC.     

Effect of various storage conditions on the stability of quinolones in raw milk

Research on the storage stability of antibiotic residues in milk is important for method development or validation, milk quality control and risk assessment during screening, confirmation, qualitative or quantitative analysis. This study was conducted using UPLC-MS/MS to determine the stability of six quinolones – ciprofloxacin (CIP), danofloxacin (DAN), enrofloxacin (ENR), sarafloxacin (SAR), difloxacin (DIF) and flumequine (FLU) – in raw milk stored under various conditions to investigate if quinolones degrade during storage of milk, and finally to determine optimal storage conditions for analysis and scientific risk assessment of quinolone residues in raw milk. The storage conditions included different temperatures and durations (4°C for 4, 8, 24 and 48 h; –20°C for 1, 7 and 30 days; –80°C for 1, 7 and 30 days), thawing temperatures (25, 40 and 60°C), freeze–thaw cycles (1–5), and the addition of different preservatives (sodium thiocyanate, sodium azide, potassium dichromate, bronopol and methanal). Most quinolones exhibited high stability at 4°C for up to 24 h, but began to degrade after 48 h. In addition, no degradation of quinolones was seen when milk samples were stored at –20°C for up to 7 days; however, 30 days of storage at –20°C resulted in a small amount of degradation (about 30%). Similar results were seen when samples were stored at –80°C. Moreover, no losses were observed when frozen milk samples were thawed at 25, 40 or 60°C. All the quinolones of interest, except sarafloxacin, were stable when milk samples were thawed at 40°C once and three times, but unstable after five freeze–thaw cycles. Preservatives affected the stability of quinolones, but the effects differed depending on the preservative and quinolone. The results of this study indicate optimum storage protocols for milk samples, so that residue levels reflect those at the time of initial sample analysis, and should improve surveillance programmes for quinolones in raw milk.     

A Novel Molecularly Imprinted Polymer Based on Carbon Nanotubes for Selective Determination of Dioctyl Phthalate from Beverage Samples Coupled with GC/MS

Phthalates represent a potential risk for humans, since they are ubiquitous environmental contaminants. Efficient extraction and purification procedures are demanded for the detection of low concentration levels of phthalates. In this work, a novel type of molecularly imprinted polymers coated onto the surface of vinyl functionalized multi-walled carbon nanotubes was synthesized and coupled with gas chromatography–mass spectrometry (GC/MS) for the selective separation and determination of dioctyl phthalate (DOP) in beverage samples. The morphology, structure property, and thermostability of the resultant polymers were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The adsorption properties of the prepared polymers were investigated by equilibrium rebinding and competitive experiments. The resultant imprinted nanomaterials exhibited high capacity and favorable selectivity. In addition, the feasibility of the developed method using the obtained imprinted polymers as a solid-phase sorbent coupled with GC/MS for the selective isolation and determination of DOP in different beverage samples was demonstrated. Under optimal conditions, the limit of detection of the proposed method for DOP was 2.3 ng L^?1. DOP spiked at three levels of concentration in beverage samples was extracted and determined through the application of the present method, with recoveries ranging from 88.6 to 93.0 % with relative standard deviations less than 5.6 %.     

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.     

Synthesis and Evaluation of Molecularly Imprinted Polymers (MIP) with Affinity for the Polypeptide Nisin

The method of hierarchical imprinting was used for the first time in order to synthesize polymers with a high affinity for nisin. The concept of this approach is demonstrated by filling the pores of silica particles, which contain immobilized peptidic templates, with a mixture of monomers/initiator, followed by polymerization and subsequent dissolution of the silica template. This method leaves imprinted polymers with binding sites located at the surface that are capable of recognizing larger molecules with the same immobilized epitope. The results of the high-performance liquid chromatography analyses illustrate that the highest retention factors and imprinting factors of nisin on nisin C-terminal analogously imprinted polymers could be obtained with acetonitrile/water mixtures containing more than 80% water. Furthermore, nisin was strongly retained on polymers that were imprinted with a longer amino acid sequence because of better sterical accessibility of the binding sites for the C terminus of nisin. The retention of nisin (k = 21.65) under aqueous elution conditions results from selective ionic interactions and hydrophobic interactions. Furthermore, the polymers exhibited selectivity for the template Lys-Ala and the structurally related dipeptide Ala-Lys. The results of the present work show that these hierarchically imprinted polymers could be used for the chromatographic separation of the polypeptide nisin in aqueous solutions.     

Magnetic effervescent tablet-assisted ionic liquid dispersive liquid–liquid microextraction of selenium for speciation in foods and beverages

A novel, simple and rapid method based on magnetic effervescent tablet-assisted ionic liquid dispersive liquid–liquid microextraction (MEA-IL-DLLME) followed by graphite furnace atomic absorption spectrometry (GFAAS) determination was established for the speciation of selenium in various food and beverage samples. In the procedure, a special magnetic effervescent tablet containing CO₂ sources (sodium carbonate and sodium dihydrogenphosphate), ionic liquids and Fe₃O₄ magnetic nanoparticles (MNPs) was used to combine extractant dispersion and magnetic recovery procedures into a single step. The parameters influencing the microextraction efficiency, such as pH of the sample solution, volume of ionic liquid, amount of MNPs, concentration of the chelating agent, salt effect and matrix effect were investigated and optimised. Under the optimised conditions, the limits of detection (LODs) for Se(IV) were 0.021 μg l^–1 and the linear dynamic range was 0.05–5.0 μg l^–1. The relative standard deviation for seven replicate measurements of 1.0 μg l^–1 of Se(IV) was 2.9%. The accuracy of the developed method was evaluated by analysis of the standard reference materials (GBW10016 tea, GBW10017 milk powder, GBW10043 Liaoning rice, GBW10046 Henan wheat, GBW10048 celery). The proposed method was successfully applied to food and beverage samples including black tea, milk powder, mushroom, soybean, bamboo shoots, energy drink, bottled water, carbonated drink and mineral water for the speciation of Se(IV) and Se(VI) with satisfactory relative recoveries (92.0–108.1%).     

Determination of Benzalkonium Homologues and Didecyldimethylammonium in Powdered and Liquid Milk for Infants by Hydrophilic Interaction Liquid Chromatography–Mass Spectrometry

In this study, a hydrophilic interaction liquid chromatography–mass spectrometry (HILIC-MS/MS) method for the determination of benzalkonium (BAC) homologues and didecyldimethylammonium (DDAC) was developed. A satisfactory chromatographic separation of BAC homologues and DDAC was achieved using, as mobile phase, acetonitrile–aqueous 50 mM ammonium formate (pH 3.2) (93?+?7 v/v) at 0.3 mL min^?1. The elution order of BAC homologues was from benzyldimethylhexadecylammonium chloride (C₁₆-BAC) to benzyldimethyldecylammonium chloride (C₁₀-BAC), the exact opposite with respect to separation using reversed liquid chromatography. The instrumental method was successfully applied to powdered and liquid milk for infants (about 50 samples). From powdered milk samples, BAC and DDAC were extracted using 5 % formic acid in methanol for 60 min at 60 °C in an ultrasonic bath; after dilution with water and 5 % NH₄OH solution, a purification step using a weak cationic exchange column was performed. Satisfactory limit of detections (LODs) were achieved, below 1.0 μg kg^?1 and 0.05 μg L^?1 for powdered and liquid milk for infants, respectively. No sample was free of BAC homologues and DDAC, and in one powdered milk sample, the contamination level exceeded 500 μg kg^?1, the maximum level recommended by the Standing Committee on the Food Chain and Animal Health for food and feed.     

Determination of Herbicides in Milk Using Vortex-Assisted Surfactant-Enhanced Emulsification Microextraction Based on the Solidification of a Floating Organic Droplet

A vortex-assisted surfactant-enhanced emulsification–solidification liquid microextraction (VASEME-SFO) has been proposed for the determination of triazine and phenylurea herbicides in milk. 1-Dodecanol was used as the extraction solvent and dispersed into the aqueous samples by the assistance of a vortex mixer. Meanwhile, the addition of a surfactant, which was used as an emulsifier, could enhance the speed of the mass transfer from aqueous samples to the extract solvent. Acetic acid and Na₂SO₄ were applied and used to eliminate interference by proteins and fats. The influence of various parameters in the VASEME-SFO such as the type and volume of the extraction solvent, the type and concentration of the surfactant, and the vortex time, salt addition, and sample solution pH were investigated and optimized. Under optimal conditions, the limits of detection (LODs) and quantification (LOQs) reached ranges of 0.005–0.09 and 0.015–0.30 μg L^?1, respectively. Dynamic linear ranges (DLRs) of 0.2–200 and 2–400 μg L^?1 were obtained for triazine and phenylurea herbicides, respectively. The performance of the method was evaluated for extraction and determination of these herbicides in milk in micrograms per liter, and satisfactory results were obtained (RSD?<?10.6 %).     

Aflatoxin M1 in raw,UHT milk and dairy products in Sicily (Italy)

A survey on 73 milk samples from different animal breeds and 24 dairy products samples from Sicily, Italy, was carried out for the presence of aflatoxin M₁ (AFM1) by LC-fluorescence detection after immunoaffinity cleanup. AFM1 was detected in 48% and 42% of the milk and dairy samples at concentration ranges between <5.0–16.0 and <5.0–18.0 ng L^?1, respectively. Within the raw milk samples, 92% had an AFM1 content below 5.0 ng L^?1, in 7% of the cases it was in the range 5.0–10.0 ng L^?1 and 1% was contaminated between 10.0 and 20.0 ng L^?1. For the dairy products, ultra-high-temperature treated (UHT) milk, milk cream and cheese, the incidence was 42%, of which 83% contained less than 5.0 ng L^?1 and 17% contained 10.0–20.0 ng L^?1 AFM1. The levels of contamination found justify continuous monitoring for public health and to reduce consumer exposure.     

Preparation of a Hydrophilic Molecularly Imprinted Polymer and Its Application in Solid-Phase Extraction to Determine of Trace Acrylamide in Foods Coupled with High-Performance Liquid Chromatography

A hydrophilic molecularly imprinted polymer was synthesized using acrylamide (C₃H₅ON) as the template and 2-acrylamido-2-methylpropane sulfonic acid as the functional monomer. This imprinted polymer was characterized by static and kinetic adsorption experiments, and results showed that it exhibited with good recognition ability and fast adsorption–desorption dynamics toward acrylamide in an aqueous environment. Using the prepared material as sorbent, a method of molecularly imprinted solid-phase extraction coupled with high-performance liquid chromatography for analysis of acrylamide in foods was developed. Under the optimized conditions, the limit of detection (S/N?=?3) of this method for acrylamide was 72.0 ng/L, and the RSD for five replicate extractions of 10 μg/L acrylamide was 4.7 %. The blank potato samples spiked with acrylamide at different levels of 0.125, 0.250, and 0.50 μg/g were extracted and determined respectively by this developed method, and recoveries ranging from 91.5 to 95.1 % were obtained. Finally, commercial samples of twisted cruller and potato chip were quantitatively analyzed by this method.     

Molecularly Imprinted Polymer as Sorbent for Solid-Phase Extraction Coupling to Gas Chromatography for the Simultaneous Determination of Trichlorfon and Monocrotophos Residues in Vegetables

In this study, a molecularly imprinted polymer (MIP) was prepared using the mixture of trichlorfon and monocrotophos as the mixed template. The imprinted polymer was characterized and exhibited good recognition ability and fast adsorption–desorption dynamic toward the trichlorfon and monocrotophos. Using this imprinted polymer as sorbent, a new method of molecularly imprinted solid-phase extraction coupled to gas chromatography for the simultaneous determination of two organophosphate pesticides residues was developed. Under optimal condition, the linear range was 0.005–10.0 mg/l. At a loading flow rate of 2.0 ml/min for loading 100 ml, the detection limits were 0.28 μg/l for trichlorfon and 0.090 μg/l for monocrotophos, the peak area precision (RSD) for five replicates was 4.23–4.50 %. The blank rape samples spiked with two organophosphate pesticides at 0.05 and 0.1 mg/l levels were determined by this method with recoveries ranging from 89.41 % to 95.12 %. Moreover, this method was successfully applied to the quantitative detection of the trichlorfon and monocrotophos residues in leek samples.     

Application of molecularly imprinted hydrogel for the preparation of lactose‐free milk

BACKGROUND: A variety of lactose imprinted hydrogels were prepared and their binding properties were studied in comparison with blank non‐imprinted hydrogel. Methacrylamide and ethylene glycol dimethacrylate were used as functional monomer and cross‐linker, respectively. Dimethylsulfoxide was also applied as polymerisation solvent. RESULTS: Different template/monomer ratios were studied and the optimised imprinted hydrogel (MIP₂), with a lactose/methacrylamide ratio of 1:8, was selected in a rebinding test. In Scatchard analysis of MIP₂‐lactose interactions, the dissociation constant and maximum binding sites were 0.33 mmol L^?1 and 67.76 µmol g^?1 hydrogel, respectively. The selectivity of MIP₂ for lactose in aqueous media was also evaluated in comparison with different mono‐ and disaccharides. The data showed that the affinity of MIP₂ for lactose is significantly higher than other saccharides. The imprinted hydrogel was finally used as a sorbent for separation of lactose from milk. CONCLUSIONS: The results indicated that MIP₂, as an optimised imprinted hydrogel, can effectively bind lactose and decrease its concentration in milk. Copyright © 2012 Society of Chemical Industry     

Preparation and Application of a Molecular Imprinting Matrix Solid Phase Dispersion Extraction for the Determination of Olaquindox in Chicken by High Performance Liquid Chromatography

In this paper, a new method was established to extract olaquindox in chicken by matrix solid phase dispersion extraction using the molecularly imprinted polymers as solid phase materials. The polymers were prepared using olaquindox as the template, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the cross-linking agent. The imprinted material was characterized by static and kinetic adsorption experiments. The results showed that it had good recognition, selective ability, and fast adsorption–desorption dynamics for olaquindox. The prepared material was used as solid phase materials of matrix solid phase dispersion to enrich the olaquindox and then determined by high performance liquid chromatography. Under the optimized conditions, the range of recovery spiked with olaquindox at 1.0 and 2.0 μg?g^?1 levels was between 85.3 and 93.2 %.     

Simultaneous HPLC–DAD quantification of vitamins A and E content in raw,pasteurized, and UHT cow’s milk and their changes during storage

An improved extraction and HPLC method for the simultaneous extraction and quantitation of retinol, α-tocopherol, α-tocotrienol, and β-carotene was developed to analyze commercial whole/semi-skim/skim samples of raw/pasteurized/UHT milk in transparent plastic/glass bottles and Tetra Brik? containers. The sample preparation method required prior saponification at 40 °C for 15 min followed by n-hexane extraction. An isocratic acetonitrile/methanol (65:35 v/v) mobile phase, C₁₈ analytical column, and UV detector were chosen for HPLC quantification. The liposoluble vitamin content in raw, pasteurized conventional/organic, and UHT milk ranged 0.055–5.540 (retinol), 0.135–1.410 (α-tocopherol), and 0.040–0.850 mg/L (β-carotene). No significant differences (p > 0.05) were observed on losses of retinol, α-tocopherol, and β-carotene content in UHT whole milk after 5 days at 4 °C in the dark. After 14 days at 4 °C in the dark, the contents of retinol, α-tocopherol, and β-carotene remained higher in milk with higher fat content and were higher in unopened containers. In UHT whole milk, samples containing 0.02 % NaN₃, retinol (33 %), and α-tocopherol (11 %) but not β-carotene (2 %) decreased significantly (p < 0.05).     

Determination of Chlorpyrifos in Rice Based on Magnetic Molecularly Imprinted Polymers Coupled with High-Performance Liquid Chromatography

The magnetic molecularly imprinted polymers (MMIPs) were prepared and used for the selective separation of chlorpyrifos from rice samples. The MMIPs were synthesized by surface-imprinted polymerization, using functionalized Fe₃O₄ particles as magnetic cores, chlorpyrifos as template, methacrylic acid as functional monomer, and trimethylolpropane trimethacrylate as cross-linker. Magnetic particles were characterized by scanning electron microscopy, Fourier-transform infrared spectrometry, physical property measurement system, and thermogravimetric analyzer. Adsorption studies were carried out to investigate the specific binding capacity, kinetics, and recognition specificity. The kinetic property of MMIPs was well fitted to the pseudo-second-order equation. The selective recognition experiment demonstrated that MMIPs had high selectivity towards chlorpyrifos over reference compound. Chlorpyrifos extracted from the rice samples was purified with MMIPs and detected by high-performance liquid chromatography. Under the optimal conditions, the detection limit of chlorpyrifos was 0.0072 μg g^?1. The relative standard deviations of intra- and interday ranging from 2.4 to 4.6 % and from 3.5 % to 7.3 % were obtained, respectively. The recoveries of chlorpyrifos at three different fortified concentrations (0.025, 2.5, and 5 μg g^?1) were in the range of 81.2–92.1 %.     

Study on a Molecularly Imprinted Solid-Phase Extraction Coupled to Capillary Electrophoresis Method for the Determination of Trace Trichlorfon in Vegetables

How to determine the pesticide residues in vegetable is an urgent problem. In this study, we reported a new method of solid-phase extraction coupled to capillary electrophoresis (SPE–CE) based on a molecularly imprinted polymer (MIP) for determination of trace trichlorfon. The electrophoretic conditions and factors which affected the molecularly imprinted solid-phase extraction were optimized. Under optimal conditions, the linear ranges of the calibration graph were 0.1 μg/L to 10 mg/L. The limit of detection (LOD) and method quantitation limit (MQL) were 4.9 and 16.2 μg/kg, respectively. With a flow rate of 2.5 mL/min for 50 mL loading, an enrichment factor of 160 was obtained. The relative standard deviation (RSD) for five replicate extractions of 0.01 mg/L trichlorfon standard solution was 4.5 %. The blank cucumber, lettuce, and radish samples spiked with trichlorfon at three levels were extracted and determined by this presented method with recoveries ranging from 77.6 to 93.2 %. Moreover, this proposed methodology was successfully applied to the quantitative detection of the trichlorfon residues in the leek samples, and the results were in good agreement with that obtained by the gas chromatography method.     

Reproducible Molecularly Imprinted QCM Sensor for Accurate,Stable, and Sensitive Detection of Enrofloxacin Residue in Animal-Derived Foods

This study describes the development of a novel reproducible molecularly imprinted quartz crystal microbalance (QCM) sensor for the accurate and sensitive analysis of the residue of enrofloxacin (ENRO) in animal-derived foods. This proposed sensor was easily fabricated by directly immobilizing molecularly imprinted polymer (MIP) of ENRO on the surface of a QCM Au chip, which combined the advantages of selective recognition from the MIP with the high sensitivity and portability of a QCM sensor. The parameters in the fabrication and measurement process were optimized and discussed in detail. It was verified that the MIP-modified QCM Au chip performed favorably for the detection of ENRO residue in common animal-derived food products and demonstrated acceptable accuracy (recovery: pure milk 77.2–84.2%, egg 77.3–85.6%, chicken muscle 73.5–89.1%, pork 74.7–85.8%), precision (relative standard deviation (RSD, n = 3), pure milk 2.9–8.0%, egg 2.9–6.4%, chicken muscle 3.4–6.8%, pork 2.2–4.7%), and sensitivity (limit of detection, pure milk 0.31 μg L^?1, egg 0.44 μg kg^?1, chicken muscle 0.54 μg kg^?1, pork 0.57 μg kg^?1). The MIP-modified QCM Au chip for sensing ENRO was portable, could be stored for an extended period of time, and reused for more than 30 analysis cycles with a response attenuation of 7.8%. These results have demonstrated that the proposed MIP QCM sensor presents an accurate, sensitive, rapid, and low-cost methodology for ENRO residue detection in animal foods. This research is very promising for the development of novel effective devices applied to the detection of various contaminants in the field of food safety.     

A Preconcentration Procedure for Determination of Ultra-Trace Mercury (II) in Environmental Samples Employing Continuous-Flow Cold Vapor Atomic Absorption Spectrometry

New functionalized magnetic nanoparticles as solid-phase sorbent were prepared and investigated for extraction of ultra-trace amounts of mercury from environmental samples. The Fe₃O₄ magnetic nanoparticles functionalized with dithizone were characterized by Fourier transform infrared spectrometer. X-ray diffraction and scanning electron microscopy confirmed the size of nanoparticles. Effects of several factors on the extraction procedure were investigated. The optimized conditions were established to be 80 mg of polymer, 8.5 for solution pH, 5 min for adsorption time, 5 min for desorption time, 2 mL for HCl (0.1 mol L^?1)/ thiourea 0.05 % as the eluent, 500 mL for breakthrough volume, and without addition of salt. Under the optimal conditions, the limit of detection, maximum capacity, and preconcentration factor were 0.05 ng mL^?1, 0.557 mmol g^?1, and 250, respectively. Limit of quantification was in the range of 0.2–2 ng mL^?1 for various matrices. Accuracy and precision of the method were about ±2.0 and below 11.1 %, respectively. Finally, the present method has been successfully applied to mercury determination in table salt, green tea, vegetables, toothpaste, and water samples. The mercury content found in the real samples was from 0.6 to 15.74 ng mL^?1 without addition of mercury.     

The emulsifying properties of Persian gum (Amygdalus scoparia Spach) as compared with gum Arabic

The current study compares the emulsifying properties of Persian gum (PG) and gum Arabic (GA) in emulsions. The effects of concentration (0.5–3% w/v PG, 2.5–15% w/v PG), pH (2–7), ionic strength [NaCl, CaCl₂ (0–300 mM)], and temperature (40–90°C) were investigated. The surface–volume mean diameter (D₃₂) of the emulsions showed that the minimum values were 9.89 ± 0.68 and 4.52 ± 0.03 µm for emulsions containing 1.5% w/v PG and 15% w/v GA, respectively. In addition, the zeta potential of PG and GA emulsion changed from ?23.5 to ?39.5 and ?30.5 to ?46.0 mV, respectively. The interfacial tensions of PG and GA emulsions were varied in the ranges of 34.0–15.0 and 29.0–9.0 mN/m, respectively. Changes in the D₃₂ value of GA emulsions showed were not significantly different (p > 0.05) with respect to the effects of pH, NaCl, CaCl_2, and temperature. The NaCl concentration had no significant effect on D₃₂; but its value decreased from 13.11 to 5.70 µm as the CaCl₂ concentration increased. The interfacial tension of PG significantly increased with decreasing pH 7–2 and increasing 0–300 mM salts. After heating (25–90°C), the D₃₂ values of PG and GA emulsions changed to 11.04–14.54 and 4.21–4.21 μm, respectively. The results of this study can be useful for the application of PG as an emulsifier in beverage emulsions.