Chifang Peng

Evaluation and interlaboratory validation of a GC-MS method for analysis of pesticide residues in teas

A method was described for simultaneous determination of nine organic heterocyclic pesticide residues by gas chromatography-mass spectrometry-selected ion monitoring. Atrazine, vinclozolin, procymidone, triflumizole, imazalil, buprofezin, propiconazole, fenarimol, and pyridaben were clearly separated from each other, extracted with acetone—hexane mixture, purified with graphitized carbon black cartridge and neutral Al2O3 cartridge, eluted with acetone—hexane mixture, simultaneously determined by GC-MS, and then quantified with an external standard method. Recoveries of pesticides ranged from 73 % to 116 % at the spiked level of 0.01–30 mg kg−1, while the relative standard deviation was between 3 % and 27 %. In addition, the limits of determination (0.01 mg kg−1 to 5.0 mg kg−1) and linearity (0.02–40 μg mL−1) revealed that simultaneous determination of multi-residues in Chinese teas (like Oolong tea, green tea, red tea, etc.) was possible. Furthermore, an interlaboratory study among 5 labs was conducted to further validate the method, and the results were satisfactory.

Development of colloidal gold-based immunochromatographic assay for the rapid detection of medroxyprogesterone acetate residues

Abstract One-step membrane-based competitive colloidal gold-based immunoassays in lateral-flow formats for the rapid detection of medroxyprogesterone acetate (MPA) were developed. Nitro-cellulose membrane strip was separately coated with goat anti-rabbit IgG (control line) and MPA hapten-OVA conjugate (test line). Anti-MPA polyclonal antibody labelled with colloidal gold particles was firstly incubated with MPA. A positive reaction as a result of the remaining antibody-gold conjugate combining with antigen coated on the membrane was obvious by visual detection, with detection limits for lateral flow of 5 µg/kg for detecting MPA standard solution, and the limit of detection was 10 µg/kg for detecting the MPA spiked in swine urine and liver. The assay time for test was less than 5 min, suitable for rapid testing on-site.

Comparative Analysis of Medroxyprogesterone Acetate Residue in Animal Tissues by ELISA and GC‐MS

Abstract Medroxyprogesterone acetate is a xenobiotic growth promoter of meat‐producing animals. In this study, the liver, kidney, and muscle of rabbits were obtained after the medroxyprogesterone acetate was administrated successively for 5 days at 0.8 mg/kg and withdrawn for 7 days before slaughter. The medroxyprogesterone acetate residues were determined by ELISA method. The average residue in muscle, liver, and kidney, as 7, 6, and 23 µg/kg, respectively. Residues were confirmed by GC/MS by monitoring four ions, 373, 283, 265, and 145 m/z. A good correlation was observed between the GC/MS and ELISA methods.

Separation and identification of synthetic antigens of hexoestrol residue in animal derived food by HPLC-MS

Abstract Hexoestrol and its derivatives, hexoestrol-mono-ether-butyrate-ethyl (HES-MEBE), hexoestrol-di-ether-butyrate-ethyl (HES-DEBE) were separated and identified using liquid chromatography and spectrometry (ESI). The conditions were as follows: Methyl alcohol and water as mobile phase, 0.3 ml/min of flow rate, elution with linear gradient concentrations from 60–100% of methanol for 25 min on a Lichrospher C-18 column. Synthetic antigen was prepared by coupling hexoestrol-mono-caroxyl-propyl-ethyl (HES-MCPE) with carrier protein by the mixed anhydride method, and the conjugation rate, analysed by UV scanning, is 36.

Simultaneous Determination 9 Anabolic Steroids Residues in Animal Muscle Tissues by Gas Chromatography‐Mass Spectrometry

Abstract A method was developed for determining 9 anabolic steroids (ASs) residues in animal muscle tissues by gas chromatography‐mass spectrometry (GC/MS). After undergoing enzymolysis, being homogenized, and then being picked‐up by ultrasound the sample was extracted with tert‐Butyl methyl ether, cleaned up through solid‐phase extraction (SPE) based on the reverse phase (RP) principle, and after derivatization of the analyst of interest, analyzed by GC/MS under selective ion monitoring (SIM). The limits of the detection (LOD) of the GC/MS method used for testing epitestosterone (ETS), nandrolon (17β‐NT), 17α‐methyl‐testosterone (MTS), testosterone 17‐propionate (PTS), 17β‐estradiol 3‐benzoate (BES), estrone (ESN), 17β‐estradiol (17β‐ES), 17α‐ethynylestradiol (EES), and estriol (EST) in animal muscle ranged from 0.10 to 0.33 µg/kg and the limits of quantification (LOQ) were from 0.24 to 0.82 µg/kg. The experiments using spiked samples, such as pork, beef, chicken, and fish, made it clear that at addition level of 2.0 µg/kg, the average recovery of the ASs ranged from 62.5% to 80.5%, and the coefficient of variation ranged from 12.5% to 26.8%, while at an addition level of 5.0 µg/kg, the average recovery was from 70.8% to 86.4%, and the coefficient of variation was from 8.8% to 18.4%.

Synthesis and identification of immunogen medroxyprogesterone acetate residues in edible foods and preparation of the Antisera

Medroxyprogesterone acetate (MPA), relative molecular mass is only 344.5 and it has no immunogenecity. The methods of the carbodiimides and the mixed anhydride were both adopted to couple MPA with bovine serum albumin, the carrier protein. The coupling rates of conjugate using the above methods were estimated to be 14 and 20 by ultraviolet spectrophotometry. The coupling was successful according to the analysis of SDS-PAGE illustration. New Zealand white rabbits were immunized with the conjugate the coupling rate of which was 14, and blood was collected after five periods of immunities. Then the titre of antiserum was tested to be 2.6 × 105 by indirect ELISA, which further identified the success of coupling.

Development of colloidal gold-based immumochromatographic assay for the rapid detection of medroxyprogesterone acetate residues in biological materials

A competitive colloidal gold-based immunoassay in lateral-flow format for the rapid detection of medroxyprogesterone acetate (MPA) in biological materials was developed. A nitro-cellulose membrane strip was separately coated with goat anti-rabbit IgG (control line) and MPA hapten-OVA conjugate (test line). Anti-MPA polyclonal antibody labelled with colloidal gold particles was first incubated with MPA. The limit of detection for lateral flow was 5 ng g−1 for detecting an MPA standard solution, and the limit of detection was 10 ng mL−1 for detecting the MPA spiked in pig urine and 10 ng g−1 for spiked in pig liver. The results were confirmed by high-performance liquid chromatography tandem mass spectrometry (HPLC/MS/MS) and indicated that there was a good agreement between both methods (R 2 = 0.976). The assay time for the test was less than 5 min, suitable for rapid testing on site.