No abstract

A broad-specificity immunoassay was established to monitor marbofloxacin (MBF) and ofloxacin (OFX) residues in raw milk and porcine muscle samples. The main influential parameters in the assay buffer were investigated to improve the assay performance. The cross-reactivities (CRs) were lower than 0.25%, except for OFX (41.38%). The quantitative working ranges for MBF and OFX based on fortified matrices ranged from 0.11 to 30.85 ng mL −1 , with a 50% inhibitory concentration of 0.76±0.12 ng mL −1 for MBF and 2.70±0.28 ng mL −1 for OFX. The detection limits of enzyme-linked immunosorbent assay (ELISA) ranged from 0.053 to 0.358 ng mL −1 in spiked samples. The mean recoveries were in the range of 80.52-95.46%, less than 12.06% of the coefficient of variation. A good correlation between the ELISA results and those from instrument methods demonstrated the practical application of the novel ELISA. Therefore, the immunoassay proposed is feasible for MBF and OFX analysis in animal-derived foods.

We report a novel method for simultaneous determination of cyromazine and melamine based on a molecularly imprinted monolith on-line coupled with high performance liquid chromatography (HPLC). The imprinted monolith was prepared by in situ polymerization using 2,4-diamino-6-undecyl-1,3,5-triazine (DAUTA) as a mimic template. Due to the better solubility of DAUTA in chloroform, hydrogen bonds were effectively developed between the template and the functional monomer and resulted in the formation of highly specific cavities in the obtained imprinted monolith. With methanol as the loading solvent, cyromazine and melamine were both selectively retained by the obtained imprinted monolith, while the nonspecific adsorption on the non-imprinted monolith was negligible. The imprinted monolithic column was on-line coupled with HPLC for purification and concentration of the two analytes from milk samples. To minimize the peak broadening during the on-line transfer of the analytes from the imprinted monolith to the following analytical column, a successive desorption program was developed for the elution step, which enabled on-line stacking of the target compounds before being analyzed by HPLC. Low detection limits of 0.12 μg mL(-1) for melamine and 0.05 μg mL(-1) for cyromazine were achieved with only 0.3 mL of milk sample and a low sensitivity HPLC-UVD instrument. The method may be further extended to detect other analytes of interest in a large variety of samples.

Development of an indirect competitive enzyme-linked immunosorbent assay for screening ethopabate residue in chicken muscle and liver.

A new molecularly imprinted polymer (MIP)-chemiluminescence (CL) method has been developed for the detection of ethopabate (ETP) residues in chicken muscle. The MIP microspheres were prepared using precipitation polymerization with ETP as a template, methacrylic acid as a functional monomer and pentaerythritol triacrylate as a cross-linker in the porogen of acetonitrile. The prepared MIP microspheres were characterized by using a scanning electron microscope, differential scanning calorimeter and Fourier transform infrared spectrometer. The binding properties of ETP on the imprinted polymers were evaluated by the equilibrium rebinding experiment. It was revealed that two classes of binding sites were produced in the resulting ETP MIPs with the dissociation constants of 23.92 mg L À1 and 77.82 mg L À1 , and the affinity binding sites of 8808.28 mg g À1 and 14 043.90 mg g À1 , respectively. As the artificial biomimetic recognition element for ETP, the polymer microspheres were immobilized in microtiter plates (96 wells) with poly(vinyl alcohol) as a glue. Through the optimization of the MIP absorption and CL imaging conditions, ETP was quantified based on the peroxyoxalate CL reaction enhanced by imidazole. Under the optimum conditions, the relative CL intensity has a linear relationship with the ETP concentration in the range of 0.1 mg mL À1 to 30 mg mL À1 , with a limit of detection of 14.7 mg kg À1 and a limit of qualification of 20.4 mg kg À1 in chicken muscle. The recoveries of spiked ETP are in the range of 99.80% to 99.98% with a relative standard deviation of 1.7% to 3.4%. For the first time, the CL method combined with MIPs was developed to determine trace ETP in real samples, and the results show that it can become a useful analytical tool for quick detection in residue analysis.