Electrochemical behavior of β2-agonists at graphite nanosheet modified electrodes

Electrochemical sensor to detect terbutaline in biological samples by a green agent

In this research, reduced graphene oxide (RGO) which is a form of graphene oxide (GO) was formed through a reduction process using a "green agent" called Ascorbic acid (AA). RGO was then modified on the surface of the glassy carbon electrode (GCE) to generate RGO/GCE (an advanced electrode). The RGO/GCE was then used to detect Terbutaline (TB) in urine samples of volunteer athletes (n = 5) using well-known spectrophotometric analyses including X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible Spectroscopy (UV-Vis), and Raman and electrochemical methods using voltammetric analyses such as differential pulse anodic stripping voltammetry (DP-ASV) and cyclic voltammetry (CV). Comparing various analysis methods using RGO/GCE to detect TB in human urine samples, voltammetric analysis specifically DP-ASV demonstrated higher sensitivity and selectivity in detecting TB than spectrophotometric analyses. Thus, in this study, several factors that would affect the voltammetric signals such as pH and interferents were evaluated and the electroactive surface area was also calculated. Our findings indicated that the RGO/GCE showed excellent repeatability, reproducibility, and long-term stability suggesting that TB could be detected more effectively using RGO/GCE than bare GCE. The detection limit of 0.0052 μM achieved in this study indicated that RGO/GCE can effectively detect TB in human urine while demonstrating reasonable selectivity and sensitivity.

A novel microfluidic paper-based analytical device based on chemiluminescence for the determination of β-agonists in swine hair

β-Agonists are illegal feed additives in the feed industries of many countries, especially China. Here, we report a microfluidic paper-based analytical device (μPAD) coupled with the chemiluminescence (CL) method to provide the sensitive, simple and rapid quantitative detection of β-agonists in swine hair samples. In this study, we found that the β-agonists diminished the CL generated by the reaction of K3[Fe(CN)6] and luminol on μPAD, which was different from that observed in the aqueous solution, and the degree of diminishment was proportional to the concentration of β-agonists. The possible mechanism was discussed as well. Also, this detection method showed a wide linear range (from 4.0 × 10-8 to 1.0 × 10-5 mol L-1) and low limit of detection (2.0 × 10-8 mol L-1) with a low consumption of samples and reagents. Satisfactory recovery values (from 78% to 95%) were achieved. Therefore, our μPAD CL sensor will be favorable to develop a miniaturized instrument for the on-site analysis of β-agonists in swine hair samples.

A highly stable black phosphorene nanocomposite for voltammetric detection of clenbuterol

A nanocomposite was prepared from graphene-like two-dimensional black phosphorene (BP, an allotrope of phosphorus) and nafion (Nf) treated with isopropanol (IP). A glassy carbon electrode (GCE) modified with this nanocomposite was found to be a viable sensor for voltammetric determination of clenbuterol (CLB). Unlike previously reported pure BP, the BP nanocomposite was stable towards water and oxygen. Its morphology, structure, electrochemically active surface area and electrochemical stability were investigated. The BP-Nf (IP) modified GCE displayed good electrochemical stability and electrocatalytic capacity with a low working potential of 0.94 V (vs. SCE), excellent peak current response for CLB in a linear concentration range of 0.06-24 μM with a detection limit of 3.7 nM (3σ/m) and a sensitivity of 0.14 μA·μM^-1·cm^-2 under optimal conditions. A sensing mechanism for the electro-oxidation of CLB was suggested and verified by density functional theory calculations under imitation of aqueous solution conditions. The sensor was successfully applied to the determination of CLB in bovine meat and bovine serum samples. Graphical abstract Highly-stable black phosphorene (BP) nanocomposite based on Nafion (Nf) was used to modify a glassy carbon electrode (GCE). It is shonw to be a viable electrochemical platform for sensitive voltammetric determination of trace clenbuterol (CLB) in bovine beef and bovine serum.

New sulfonate composite functionalized with multiwalled carbon nanotubes with cryogel solid-phase extraction sorbent for the determination of β-agonists in animal feeds

A new mixed-mode cation-exchange sulfonate composite functionalized with multiwalled carbon nanotubes with polyvinyl alcohol cryogel was fabricated and used for the first time as a solid-phase extraction sorbent for the determination of β-agonists in animal feeds. Feed samples were extracted with 0.20 M phosphoric acid and methanol (1:4, v/v) using ultrasonication, cleaned-up using the developed sorbent to which the β-agonists bound then finally eluted with 5.0% ammonia in methanol and analyzed by high-performance liquid chromatography. Various parameters that affected the extraction efficiency were optimized. Under the optimal conditions, the developed sorbent strongly interacted with β-agonists by cationic exchange and hydrophobic and hydrophilic interactions, that provided a high extraction efficiency in the range of 92.8 ± 3.7-104.4 ± 2.3% over a range of 0.04-2.0 mg/kg for salbutamol and ractopamine, and 0.40-8.0 mg/kg for clenbuterol. The relative standard deviations were less than 6.0%. The developed method was successfully applied for the determination of β-agonists in various types of animal feed and effectively reduced any matrix interference.

Electrochemical sensing of bisphenol A by graphene-1-butyl-3-methylimidazolium hexafluorophosphate modified electrode

Simple and low cost sensor for the determination of bisphenol A (BPA) based on graphene-1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) modified glassy carbon electrode was developed. It was an irreversible oxidation process of BPA on the modified electrode. Experimental conditions such as modified volume, pH, scan rate and accumulation time have been optimized. The modified electrode provided a considerable enhancement of BPA oxidation. The electrochemical response of BPA on this modified electrode was better than those on the graphene modified electrode and bare electrode. The detection limit of BPA was 8nM (S/N=3), the linear range was from 20nM to 2µM. The modified electrode has been employed for determination of milk and soda spiked BPA successfully.

Multiresidue Determination of β2-Agonists Including Phenylethanolamine A in Animal-Derived Food by Ultra-High Performance Liquid Chromatography/Tandem Mass Spectrometry

A comprehensive ultra-high performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) procedure for detection of nine β-agonists in animal-derived food is described. The method was based on enzymatic hydrolysis with β-glucuronidase from Helix pomatia, followed by a liquid-liquid extraction procedure with perchloric acid and a solid-phase extraction scheme using two kinds of cartridges, HLB and MCX. The influence of sample solution pH in the extraction recovery was studied, and pH 4.0 was found to give the best recovery. The analytes were eluted with methanol containing 4% ammonia. A validation procedure for quantitative analysis of β-agonists in animal-derived food was performed. The three kinds of internal standards, d3-salbutamol, d6-ractopamine and d9-clenpenterol, were applied in the sample preparation and detection of UHPLC/MS/MS. The recoveries from spiked samples ranged between 74.9 and 106.9%. The relative standard deviations of detection were at 0.7-9.6%. The limits of detection and quantification were 0.01-0.05 and 0.03-0.20 µg/kg, respectively. The effect of sample matrix in the detection was discussed in detail.

Monitoring of PAEMs and beta-agonists in urine for a small group of experimental subjects and PAEs and beta-agonists in drinking water consumed by the same subjects

This 5-month study contains two parts: (1) to monitor the concentrations of 11 phthalate esters metabolites (PAEMs) and two beta-agonists in human urine samples collected from a small group of consented participants including 16 females and five males; and (2) to analyze the residues of phthalate esters (PAEs) and beta-agonists in various categories of drinking water consumed by the same group of subjects. Each category of human urine and drinking water had 183 samples of its own. The analytical results showed that nine PAEMs were detected in human urine and eight PAEs were detected in drinking water samples. It was found that average concentrations of PAEMs increased as the age increased, but no significant difference between sexes. Further, using the principal component analysis, the loadings of age effect were found to be two times greater than that of gender effect in terms of four DEHP metabolites. Regarding beta-agonists of concern (i.e., ractopamine and salbutamol), they were neither detected in human urine nor drinking water samples in this study.

Sensitive voltammetric sensor based on isopropanol-Nafion-PSS-GR nanocomposite modified glassy carbon electrode for determination of clenbuterol in pork

In the present study, poly(sodium 4-styrenesulfonate) (PSS) functionalized graphene (GR) was synthesised via a simple one-step chemical reduction of exfoliated graphite oxides in the presence of PSS. Characterisation of as-made nanocomposite using Fourier transform infrared spectroscopy (FT-IR) and ultraviolet and visible spectroscopy (UV-vis) clearly demonstrate the successful attachment of PSS to graphene sheets. A novel clenbuterol (CLB) electrochemical sensor was fabricated based on isopropanol-Nafion-PSS-GR composite film modified glassy carbon electrode. In the Britton-Robinson buffer (pH 1.2), the sensor exhibited superior electrocatalytic activity towards the oxidation of CLB. Applying linear sweep voltammetry, a good linear relationship of the oxidation peak current with respect to concentrations of CLB cross the range of 7.5 × 10(-8)-2.5 × 10(-5)mol L(-1) and a detection limit of 2.2 × 10(-8) mol L(-1) were achieved. The proposed method was successfully applied for the determination of CLB in pork.

Direct detection of β-agonists by use of gold nanoparticle-based colorimetric assays

β-Agonists fed to animals for human consumption pose a serious threat to human health. Fast, broad-spectrum detection methods are needed for on-site screening of various types of β-agonists from animal feeds, meats, and animal body fluids. We developed a colorimetric assay that uses gold nanoparticle (AuNP) plasmon absorption to realize quick detection of β-agonists from liquid samples. β-Agonists showed the capability of directly reducing HAuCl(4) into atomic gold, which involved oxidation of the amine or phenol group on the benzene ring of the β-agonists. The resulting atomic gold formed AuNPs spontaneously, which had strong plasmon absorption at 528 nm. The linear relationship between the concentrations of β-agonists and the AuNPs plasmon absorbance granted quantitative determination of β-agonists in solution. The AuNPs colorimetric assay showed different sensitivities toward β-agonists with different substituent groups on the aromatic ring. β-Agonists with phenol groups had a lower limit of quantitation (LOQ) than those with amine groups. High-resolution transmission electron microscopy (TEM) images revealed the sizes of the AuNPs were in the range 15-25 nm, while X-ray energy-dispersive spectroscopic data suggested the smaller particles observed in TEM with lower contrast may be salt particles from the buffer solution. The developed colorimetric assay can potentially be used for the detection of β-agonists and their analogues from serum, urine, and other liquid samples in the presence of interference from common antibiotics and glucose.

Single-Walled-Carbon-Nanotube-Modified Pyrolytic Graphite Electrode Used as a Simple Sensor for the Determination of Salbutamol in Urine

A fast and sensitive voltammetric method has been proposed for the determination of salbutamol at single-walled-carbon-nanotube-modified edge-plane pyrolytic graphite electrode (SWNT/EPPGE) in human urine. The electrochemical response of salbutamol was determined by square wave voltammetry (SWV) in phosphate buffer solution (PBS) at physiological pH 7.2. The modified electrode showed improved voltammetric response towards the oxidation of salbutamol, and a well-defined anodic peak was observed at~600 mV with enhanced peak current in comparison to the bare electrode. Linear calibration plot using SWNT/EPPGE was obtained in the concentration range of 50 to 2500 ngml-1with sensitivity and detection limit of 2.15 nA/ngml-1and 4.31 ngml-1, respectively. The developed method has been successfully applied for the determination of salbutamol in commercial preparations and human body fluids. Fast analysis of salbutamol in human urine makes the proposed method of great interest for doping control purposes at the site of competitive games.