Combined microextraction by packed sorbent and high-performance liquid chromatography–ultraviolet detection for rapid analysis of ractopamine in porcine muscle and urine samples

Magnetic solid-phase extraction based on restricted-access molecularly imprinted polymers for ultrarapid determination of ractopamine residues from food samples by capillary electrophoresis

An ultrafast, efficient, and eco-friendly method combining magnetic solid phase extraction and capillary electrophoresis with diode array detection have been developed to determine ractopamine residues in food samples. A restricted access material based on magnetic and mesoporous molecularly imprinted polymer has been properly synthesized and characterized, demonstrating excellent selectivity and high adsorbent capacity. Short-end injection capillary electrophoresis method was optimized: 75 mM triethylamine pH 7 as BGE, -20 kV, 50 mbar by hydrodynamic injection during 8 s, and capillary temperature at 25 °C; reaching ultrafast ractopamine analysis (∼0.6 min) with good peak asymmetry, and free from interfering and/or baseline noise. After sample preparation optimization, the conditions were: 1000 µL of sample at pH 6, 20 mg of adsorbent, stirring time of 120 s, 250 µL of ultrapure water as washing solvent, 1000 µL of methanol: acetic acid (7: 3, v/v) as eluent, and the adsorbent can be reused four times. In these conditions, the analytical method showed recoveries around to 100 %, linearity ranged from 9.74 to 974.0 µg kg-1, correlation coefficient (r) ≥ 0,99 in addition to adequate precision, accuracy, and robustness. After proper validation, the method was successfully applied in the analysis ractopamine residues in bovine milk and bovine and porcine muscle.

Core-Satellite Nanoassemblies as SPR/SERS Dual-Mode Plasmonic Sensors for Sensitively Detecting Ractopamine in Complex Media

Highly sensitive and reliable detection of β-adrenergic agonists is especially necessary due to the illegal abuse of growth-promoting feed additives. Here, we develop a novel surface plasmon resonance/surface-enhanced Raman scattering (SPR/SERS) dual-mode plasmonic sensor based on core-satellite nanoassemblies for the highly sensitive and reliable detection of ractopamine (RAC). The addition of RAC results in the decomposition of core-satellite nanoassemblies and consequently changes the Rayleigh scattering color of dark-field microscopy (DFM) images and the Raman scattering intensity of SERS spectra. The excellent sensitivity, specificity, and uniformity of this strategy were confirmed by detecting RAC in various complex media in the farm-to-table chain, and the limit of detection (LOD) was 0.03 ng/mL in an aqueous solution. In particular, the convenient access to livestock sewage not only ensures animal welfare but also provides great convenience for the market regulation of β-agonists. The success of our on-site strategy only with a portable Raman device promises great application prospects for β-agonist detection.

Au Nanoparticles Functionalized Covalent-Organic-Framework-Based Electrochemical Sensor for Sensitive Detection of Ractopamine

Ractopamine, as a feed additive, has attracted much attention due to its excessive use, leading to the damage of the human nervous system and physiological function. Therefore, it is of great practical significance to establish a rapid and effective method for the detection of ractopamine in food. Electrochemical sensors served as a promising technique for efficiently sensing food contaminants due to their low cost, sensitive response and simple operation. In this study, an electrochemical sensor for ractopamine detection based on Au nanoparticles functionalized covalent organic frameworks (AuNPs@COFs) was constructed. The AuNPs@COF nanocomposite was synthesized by in situ reduction and was characterized by FTIR spectroscopy, transmission electron microscope and electrochemical methods. The electrochemical sensing performance of AuNPs@COF-modified glassy carbon electrode for ractopamine was investigated using the electrochemical method. The proposed sensor exhibited excellent sensing abilities towards ractopamine and was used for the detection of ractopamine in meat samples. The results showed that this method has high sensitivity and good reliability for the detection of ractopamine. The linear range was 1.2-1600 μmol/L, and the limit of detection (LOD) was 0.12 μmol/L. It is expected that the proposed AuNPs@COF nanocomposites hold great promise for food safety sensing and should be extended for application in other related fields.

Ractopamine at the Center of Decades-Long Scientific and Legal Disputes: A Lesson on Benefits, Safety Issues, and Conflicts

Ractopamine (RAC) is a synthetic phenethanolamine, β–adrenergic agonist used as a feed additive to develop leanness and increase feed conversion efficiency in different farm animals. While RAC has been authorized as a feed additive for pigs and cattle in a limited number of countries, a great majority of jurisdictions, including the European Union (EU), China, Russia, and Taiwan, have banned its use on safety grounds. RAC has been under long scientific and political discussion as a controversial antibiotic as a feed additive. Here, we will present significant information on RAC regarding its application, detection methods, conflicts, and legal divisions that play a major role in controversial deadlock and why this issue warrants the attention of scientists, agriculturists, environmentalists, and health advocates. In this review, we highlight the potential toxicities of RAC on aquatic animals to emphasize scientific evidence and reports on the potentially harmful effects of RAC on the aquatic environment and human health.

Electrospun nanofibers modified with zeolitic imidazolate framework-8 for electrochemiluminescent determination of terbutaline

For the first time it is demonstrated that zeolitic imidazolate framework-8 electrospun nanofibers (ZIF-8 NF) could serve as electrochemiluminescence (ECL) accelerator for the facile detection of terbutaline residual. A novel ECL sensor for the determination of terbutaline was fabricated based on ZIF-8 NF. The ZIF-8 NF were successfully prepared according to electrospinning and in-situ growth method. First, chitosan was modified on the surface of the electrode, and then the ZIF-8 NF was modified onto the upper layer of the chitosan. Taking advantages of chitosan and ZIF-8 NF in conductivity and electrocatalysis, the modified electrode presents obvious ECL phenomenon in 0.2 M PBS solution (pH 10.0) containing 0.025 M luminol. After the addition of terbutaline, ECL intensity decreased significantly, and the decreasing value showed a linear relationship with the logarithm of terbutaline concentration. The linear range was from 2.0 × 10^-10 to 2.0 × 10^-5 M, and the detection limit was 1.41 × 10^-11 M (3σ/m). The method had high sensitivity, good stability, and good applicability to actual pork samples.

In-tube solid phase microextraction and determination of ractopamine in pork muscle samples using amide group modified polysaccharide-silica hybrid monolith as sorbent prior to HPLC analysis

A facile in-tube solid phase microextraction (in-tube SPME) procedure was developed to enrich ractopamine before HPLC-UV analysis. This was achieved by employing amide groups modified polysaccharide-silica hybrid monolith as an efficient sorbent. The monolith was synthesized by a simple reaction with agarose oxide and tetramethoxylisane, followed by the modification of amide groups via subsequent ring opening, "thiol-ene" click and dehydration reactions. Under the optimized extraction conditions, the enrichment factors for ractopamine, dopamine, clenbuterol, para-methylphenol and phenol were determined to be 50.5, 32.2, 4.8, 2.1 and 1.8, respectively. The monolithic column has ideal selectivity for ractopamine. Coupled with HPLC-UV, this method demonstrated a linearity within 2.0-800 ng/g for ractopamine with spiking in pork muscles (R² = 0.9958). The LOD was 0.64 ng/g (S/N = 3) and recoveries ranged from 85.2 to 108.1% (n = 3). This approach provides a feasible way for analysis of trace ractopamine in biological samples.

Ultramarine blue nanoparticles as a label for immunochromatographic on-site determination of ractopamine

A competitive immunochromatographic assay (ICA) is presented and used for on-site determination of ractopamine (RAC). Ultramarine blue nanoparticles were directly separated from ultramarine blue industrial products by centrifugation (< 10,000 rpm and > 4000 rpm) and used as visible labels in ICAs. The ultramarine blue nanoparticles were coated by polyacrylic acid (PAA), which provides carboxyl groups on the surface of ultramarine blue nanoparticles. An anti-RAC monoclonal antibody (mAb) was covalently immobilized on the carboxyl-modified ultramarine blue nanoparticle surface via diimide-activated conjugation between the carboxyl groups on the ultramarine blue nanoparticle surface and the amino groups of the antibodies. RAC and BSA-modified RAC competitively bind to the anti-RAC mAb on the ultramarine blue nanoparticles. The blue band in the test line is generated by the accumulation of ultramarine blue nanoparticles and is negatively associated with the RAC content. Under optimal conditions, the visual limit of detection (vLOD) of this ICA for RAC is 2.0 ng mL^-1, 2.0 ng mL^-1, and 1.0 ng mL^-1 in phosphate-buffered saline (PBS), feed samples, and pork samples, respectively. The ultramarine blue nanoparticle-based ICA also shows no cross activity with salbutamol, clorprenaline, clenbuterol, or terbutaline. Graphical abstract Schematic representation of the ultramarine blue nanoparticles immunochromatographic assay for detection of ractopamine (RAC) based on competitive method. The ultramarine blue nanoparticles were screened from commercial ultramarine pigments for the first time and used to detect ractopamine.

Sonochemical synthesis of perovskite-type barium titanate nanoparticles decorated on reduced graphene oxide nanosheets as an effective electrode material for the rapid determination of ractopamine in meat samples

A simple and facile ultrasound based sonochemical method to incorporate Perovskite-type barium titanate (BaTiO₃) nanoparticles inside the layered and reduced graphene oxide sheets (rGOs) is reported. BaTiO₃@rGOs nanocomposite was characterized by FESEM, HRTEM, EDX, mapping, XRD, XPS and EIS. The results show that the decoration and also incorporation of BaTiO₃ nanoparticles in the multi-layered and ultrasound reduced graphene oxide matrix. Non-enzymatic and differential pulse voltammetric sensor of ractopamine (food toxic) based on the BaTiO₃@rGOs nanocomposite modified screen printed carbon electrode is developed. Compared with the original BaTiO₃/SPCE and rGOs/SPCE, the BaTiO₃@rGOs/SPCE displays excellent current response towards ractopamine and gives linearity in the range of 0.01-527.19 µM ractopamine in neutral phosphate buffer (pH 7.0). The BaTiO₃@rGOs nanocomposite modified sensor also exhibits valuable ability of anti-interference to electroactive analytes. Furthermore, the as-prepared BaTiO₃ NPs@rGOs/SPCE has been applied to the determination of ractopamine in pork and chicken samples.

Detection of okadaic acid (OA) and tetrodotoxin (TTX) simultaneously in seafood samples using colloidal gold immunoassay

Tetrodotoxin (TTX) is a neurotoxin mainly responsible for severe neurological illness, and okadaic acid (OA) is another important lipophilic toxin to humans. In this study, we developed a gold strip for simultaneous detection of OA and TTX in real seafood samples. In the assay, the prepared nanoparticles (about 40 nm) was applied to conjugate with specific monoclonal antibodies against OA and TTX, and the resulted mixtures were used to capture its corresponding toxin in test strip. OA and TTX conjugates were coated as two test lines on the nitrocellulose membrane, and goat anti-mouse IgG was used to form the control line, forming three lines on the test strip. The visual detection limits (vLOD) of this immunoassay for OA and TTX were 0.75 and 15 ng/mL, respectively, and no cross reactions were observed in the process of detection. The visual assay for OA and TTX detection could be finished within 10 min. This study might provide a feasible method and good understanding for rapidly simultaneous detection for toxins based on immunoassay.

A novel colorimetric immunosensor based on platinum colloid nanoparticles immobilized on PowerVision as signal probes and Fe3 O4 @β-cyclodextrin as capture probes for ractopamine detection in pork

BACKGROUND

A novel colorimetric immunosensor was developed for the simple, sensitive and selective detection of ractopamine (RAC) based on using β-cyclodextrin-modified Fe₃ O₄ particles (Fe₃ O₄ @β-CD) as capture probes and complex platinum colloid nanoparticles (PtNPs-PV) composed of platinum colloid nanoparticles (PtNPs) and polymerase chelate PowerVision (PV) as signal probes.

RESULTS

PtNPs-PV double catalyzed the chromogenic substrate 3,3'-diaminobenzidine (DAB), which induced changes in the color of DAB and chromogenic absorbance. Incubation temperature, pH and incubation time were systematically optimized and, under optimum conditions, the measured absorbance values showed a linear relationship with the RAC concentrations in the range 0.03-8.1 ng mL^-1 . The detection limit was 0.01 ng mL^-1 . The sensor exhibited high sensitivity and specificity, as demonstrated by testing structurally similar organic compounds such as salbutamol, clenbuterol and dopamine. The practicality of the developed colorimetric immunosensor was supported by the successful detection of RAC in pork samples with recovery ranging from 94.00% to 106.00%.

CONCLUSION

We designed a novel sandwich-type noncompetitive colorimetric immunoassay for the detection of trace levels of RAC in pork. The proposed method can also be used for the detection of toxins in food products via PtNPs-PV amplification. © 2018 Society of Chemical Industry.

Novel ractopamine-protein carrier conjugation and its application to the lateral flow strip test for ractopamine detection in animal feed

In this work, a novel conjugate of ractopamine and bovine serum albumin (RAC-BSA) has been developed via the Mannich reaction, with a mole coupling ratio for RAC-BSA of 9:1. The proposed conjugation method provides a simple and one-step method with the use of fewer reagents compared with other conjugation methods for competitive immunoassays. RAC-BSA conjugation was used to fabricate a competitive lateral flow strip test for RAC detection in animal feed. For sample preparation, RAC was spiked in swine feed purchased from the local markets in Thailand, and methanol and running buffer at a volume ratio of 10:90 was used as extraction buffer. The procedures for sample preparation were completed within 25 min. Under optimal conditions, the limit of detection (LOD), assessed by the naked eye within 5 min, was found to be 1 ng/g. A semi-quantitative analysis was also conducted using a smart phone and computer software, with a linearity of 0.075-0.750 ng/g, calculated LOD of 0.10 ng/g, calculated limit of quantitation of 0.33 ng/g, and good correlation of 0.992. The recoveries were found in the range of 96.4%-103.7% with a relative standard deviation of 2.5%-3.6% for intra- and inter-assays. Comparison of the results obtained by the strip test with those obtained by enzyme-linked immunosorbent assay had a good agreement in terms of accuracy. Furthermore, this strip test exhibited highly specific RAC detection without cross reactivity with related compounds. Therefore, the RAC-BSA conjugation via the Mannich reaction can be accepted as a one-step and easy conjugation method and applied to the competitive lateral flow strip test.

Current trends on microextraction by packed sorbent – fundamentals, application fields, innovative improvements and future applications

MEPS, the acronym of microextraction by packed sorbent, is a simple, fast and user- and environmentally-friendly miniaturization of the popular solid-phase extraction technique (SPE).

Ephedrine Analysis in Real Urine Sample via Solvent Bar Microextraction Technique Coupled with HPLC-UV and Chemometrics

Background:

Ephedrine, an alpha/beta-adrenergic agonist, is one of the most common doping agents not only among athletes but also the ordinary people, therefore its detection at low trace levels with a sensitive and cost effective method has become a priority to investigate many analytical methods.

Objective:

In this work, solvent bar microextraction followed by high-performance liquid chromatography (HPLC-UV) was used for extraction and determination of ephedrine at low trace levels from urine samples at optimum condition.

Methods:

In this study, a designed experiment was carried out using solvent bar microextraction technique, which has been proved to be a green method. This method requires three phases consisting of a donor phase with an alkaline pH, an acceptor phase with an acidic pH, and organic solvent to impregnate the pores of the hollow fiber. The obtained results were used for estimating the optimum ranges for each parameter, analyzing the effect of different parameters, simultaneously.

Results:

Under optimized circumstances, the preconcentration factor was 129. The calibration curves represented good linearity for urine sample with coefficient estimations higher than 0.9991. The limit of detection and quantitation for ephedrine were 16.7 µg L-1 and 50 µg L-1, respectively. The relative standard deviations of analysis were 3.5% within a day (n=3) and 4.1% between days (n=9).

Conclusion:

According to the results and previous studies, it can be concluded that the preconcentration factor for ephedrine was the best result ever reported considering selectivity and cost-effectiveness.

Fabrication of Metal-Substituted Polyoxometalates for Colorimetric Detection of Dopamine and Ractopamine

A novel colorimetric detection method based on the peroxidase-like activity of metal-substituted polyoxometalates (POMs) of SiW₉M₃ (M = Co²⁺, Fe³⁺, Cu²⁺, Mn²⁺) has been established. POMs can catalyze oxidation of dopamine (DA) and ractopamine (RAC) by H₂O₂ in aqueous solutions. SiW₉Co₃-based POMs detect DA at concentrations as low as 5.38 × 10⁻⁶ mol·L⁻¹ simply by observation of the color change from colorless to orange using the naked eye. RAC is detected by observing the change from colorless to slight red by SiW₉Cu₃ with a detection limit of 7.94 × 10⁻⁵ mol·L⁻¹. This study shows that colorimetric DA and RAC detection using SiW₉Co₃ and SiW₉Cu₃ is highly selective and sensitive as well as visually observable.

Application of QuEChERS for Determining Xenobiotics in Foods of Animal Origin

The use of pesticides and veterinary drugs results in the appearance of residues of xenobiotics in foods. Thus, several methods have been developed for monitoring them; however, most are tedious and expensive. By contrast, the QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) methodology involves a microextraction that yields small samples and has been applied for the analysis of various xenobiotics including pesticides, antibiotics, and mycotoxins. QuEChERS has shown advantages over other techniques including fast sample preparation, reduced needs for reagents and labware, and versatility. This approach allows the simultaneous determination of pesticides with various polarities and volatilities and can be easily modified for the analysis of a wide range of xenobiotics in various matrices including animal products rich in fat. Nevertheless, to attain high recoveries, the extraction, cleanup, and concentration steps have to be optimized according to the target compounds and matrix. Hence, QuEChERS is a promising and environmentally friendly methodology for the high-throughput routine analysis of xenobiotics in animal products. This review focuses on the application of QuEChERS to foods of animal origin and describes recent developments for the optimization of the analysis of veterinary drugs, pesticides, polycyclic aromatic hydrocarbons, and other compounds of concern.

Advantages of time-resolved fluorescent nanobeads compared with fluorescent submicrospheres, quantum dots, and colloidal gold as label in lateral flow assays for detection of ractopamine

Label selection is a critical factor for improving the sensitivity of lateral flow assay. Time-resolved fluorescent nanobeads, fluorescent submicrospheres, quantum dots, and colloidal gold-based lateral flow assay (TRFN-LFA, FM-LFA, QD-LFA, and CG-LFA) were first systematically compared for the quantitative detection of ractopamine in swine urine based on competitive format. The limits of detection (LOD) of TRFN-LFA, FM-LFA, QD-LFA, and CG-LFA were 7.2, 14.7, 23.6, and 40.1pg/mL in swine urine samples, respectively. The sensitivity of TRFN-LFA was highest. In the quantitative determination of ractopamine (RAC) in swine urine samples, TRFN-LFA exhibited a wide linear range of 5pg/mL to 2500pg/mL with a reliable coefficient of correlation (R²=0.9803). Relatively narrow linear ranges of 10-500pg/mL (FM-LFA) and 25-2500pg/mL (QD-LFA and CG-LFA) were acquired. Approximately 0.005µg of anti-RAC poly antibody (pAb) was used in each TRFN-LFA test strip, whereas 0.02, 0.054, and 0.15µg of pAb were used in each of the FM-LFA, QD-LFA, and CG-LFA test strips, respectively. In addition, TRFN-LFA required the least RAC-BSA antigens and exhibited the shortest detection time compared with the other lateral flow assays. Analysis of the RAC in swine urine samples showed that the result of TRFN-LFA was consistent with that of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and a commercial enzyme-linked immunosorbent assay (ELISA) kit.

A competitive luminol chemiluminescence immunosensor based on a microfluidic chip for the determination of ractopamine

Herein, a competitive luminol chemiluminescence immunosensor based on a microfluidic chip was developed to detect ractopamine (RCT) both in phosphate buffer and swine urine samples. The immunosensor can provide a liner range of 0.5-40 ng/mL and a high sensitivity with a limit of detection of 0.97 ng/mL for RCT detection in swine urine. Good rates of recovery in negative swine urine samples were achieved over the RCT concentration ranging from 0.5 to 40 ng/mL. The proposed method offered a promising analytical scheme for the on-site determination of RCT.

Characterization of the binding of paylean and DNA by fluorescence, UV spectroscopy and molecular docking techniques

The interaction of paylean (PL) with calf thymus DNA (ctDNA) was investigated using fluorescence spectroscopy, UV absorption, melting studies, ionic strength, viscosity experiments and molecular docking under simulated physiological conditions. Values for the binding constant Ka between PL and DNA were 5.11 × 10(3) , 2.74 × 10(3) and 1.74 × 10(3)  L mol(-1) at 19, 29 and 39°C respectively. DNA quenched the intrinsic fluorescence of PL via a static quenching procedure as shown from Stern-Volmer plots. The relative viscosity and the melting temperature of DNA were basically unchanged in the presence of PL. The fluorescence intensity of PL-DNA decreased with increasing ionic strength. The value of Ka for PL with double-stranded DNA (dsDNA) was larger than that for PL with single-stranded DNA (ssDNA). All the results revealed that the binding mode was groove binding, and molecular docking further indicated that PL was preferentially bonded to A-T-rich regions of DNA. The values for ΔH, ΔS and ΔG suggested that van der Waals forces or hydrogen bonding might be the main acting forces between PL and DNA. The binding distance was determined to be 3.37 nm based on the theory of Förster energy transference, which indicated that a non-radiation energy transfer process occurred. Copyright © 2015 John Wiley & Sons, Ltd.

Multiresidue Method for Analysis of β Agonists in Swine Urine by Enzyme Linked Receptor Assay Based on β2 Adrenergic Receptor Expressed in HEK293 Cells

A novel enzyme-linked receptor assay (ELRA) based on β₂-adrenergic receptor (β₂-AR) has been developed for rapid and high-throughput detection of β-adrenergic agonists (β-agonists) in urine. Human embryonic kidney cells (HEK293) were introduced as the expression system to enhance the functionality of the recombinant β₂-AR, and the attempt to detect β-agonists in swine urine using such approaches was accomplished unprecedentedly. In this article, a recombinant porcine β₂-AR was produced in the inner membrane of HEK293 cells and purified from crude membrane protein by nickel-nitrilotriacetic acid affinity chromatography. After activity identification, the recombinant receptor was used in the development of direct competitive ELRA. Several parameters such as blocking buffer and blocking process were optimized and the performance of the system was determined. The IC50 concentrations of clenbuterol, salbutamol, and ractopamine were 34, 53 and 63 μg/L, and the average recovery rates were 68.2%, 60.3% and 65.5%, respectively. ELRA based on β₂-AR shows a series of advantages such as safety, easy operation, and high efficiency, making it promising for the rapid screening of β-agonists in animal urine.

Simple and sensitive monitoring of β2-agonist residues in meat by liquid chromatography-tandem mass spectrometry using a QuEChERS with preconcentration as the sample treatment

A liquid chromatography with tandem mass spectrometric detection (LC-MS/MS) method was established for the simultaneous determination of the levels of 10 β2-agonists in meat. The samples were extracted using an aqueous acidic solution and cleaned up using a Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) technique utilising a DVB-NVP-SO3Na sorbent synthesised in-house. First, the β2-agonist residues were extracted in an aqueous acidic solution, followed by matrix solid-phase dispersion for clean-up. The linearities of the method were R(2)=0.9925-0.9998, with RSDs of 2.7-15.3% and 73.7-103.5% recoveries. Very low limits of detection (LOD) and quantitation (LOQ) of 0.2-0.9 μg/kg and 0.8-3.2 μg/kg, respectively, were achieved for spiked meat. The values obtained were lower than the maximum residue limits (MRLs) established by the EU and China. These results clearly demonstrate the feasibility of the proposed approach. The evaluated method provided reliable screening, quantification and identification of 10 β2-agonists in meat.