Wenjun Gui

Simultaneous Determination of Seven Neonicotinoid Pesticide Residues in Food by Ultraperformance Liquid Chromatography Tandem Mass Spectrometry

The present study developed an improved analytical method for simultaneous quantification of seven neonicotinoids in food by ultraperformance liquid chromatography combined with electrospray ionization triple quadrupole tandem mass spectrometry (UPLC-MS/MS) under the multiple reaction monitoring (MRM) mode. The optimization of extraction, cleanup, UPLC separation and MS/MS parameters of analytes were especially focused on. The low limits of quantification (LOQs) of neonicotinoids ranged from 0.1 to 6 microg kg(-1). Meanwhile, reasonable recoveries (65-120%) of seven neonicotinoids for food including apple, cabbage, potato, rice, tea, milk, chicken, pork and egg were demonstrated in different spiked levels within their respective linear range (0.025-150 microg kg(-1)). The developed analytical method would be appropriate for the routine, high throughput, high sensitivity quantification of seven neonicotinoids using simple sample pretreatment.

Gold immunochromatographic assay for simultaneous detection of carbofuran and triazophos in water samples

Using a simple test for rapid identification and quantification of pesticide multiresidues in food and environmental samples is a long-cherished approach for practical monitoring purposes. Here two gold-based lateral-flow strips (strip A and strip B) were investigated for simultaneous detection of carbofuran and triazophos. For the strip A format, a bispecific monoclonal antibody (BsMcAb) against both carbofuran and triazophos was employed to prepare the immunogold probe. For the strip B format, anti-carbofuran monoclonal antibody (McAb) and anti-triazophos McAb separately labeled with colloidal gold were combined as detector reagents. By comparison of visual results from pesticide standard tests between the two formats, the strip B assay manifested higher sensitivities for both pesticides. Analysis of spiked water samples by the preferable strip indicated that the detection limits for carbofuran and triazophos were 32 and 4 microg/L, respectively. The strength of the portable one-step strip assay was in the simultaneous screening for two pesticides within a short time (8-10 min) without any equipment.

Thyroid endocrine disruption in zebrafish larvae following exposure to hexaconazole and tebuconazole.

The widely used triazole fungicides have the potential to disrupt endocrine system, but little is known of such effects or underlying mechanisms of hexaconazole (HEX) and tebuconazole (TEB) in fish. In the present study, zebrafish (Danio rerio) embryos were exposed to various concentrations of HEX (0.625, 1.25 and 2.5 mg/L) and TEB (1, 2 and 4 mg/L) from fertilization to 120 h post-fertilization (hpf). The whole body content of thyroid hormone and transcription of genes in the hypothalamic-pituitary-thyroid (HPT) axis were analyzed. The results showed that thyroxine (T4) levels were significantly decreased, while triiodothyronine (T3) concentrations were significantly increased after exposure to HEX and TEB, indicating thyroid endocrine disruption. Exposure to HEX significantly induced the transcription of all the measured genes (i.e., corticotrophin-releasing hormone (CRH), thyroid-stimulating hormone (TSHβ), sodium/iodide symporter (NIS), transthyretin (TTR), uridine diphosphate glucuronosyltransferase (UGT1ab), thyronine deiodinase (Dio1 and Dio2), thyroid hormone receptors (TRα and TRβ) in the HPT axis, but did not affect the transcription of thyroglobulin (TG). However, TEB exposure resulted in the upregulation of all the measured genes, excepting that TG, Dio1and TRα had not changed significantly. The overall results indicated that exposure to HEX and TEB could alter thyroid hormone levels as well as gene transcription in the HPT axis in zebrafish larvae.

Adsorption and desorption behavior of herbicide diuron on various Chinese cultivated soils.

The adsorption-desorption behaviors of diuron were investigated in six cultivated soils of China. The effect of system pH and temperature were also studied. The data fitted the Freundlich equation very well. The adsorption K(F) values indicated the adsorption of diuron in the six soils was in the sequence of black soil (D)>yellow earth (F)>paddy soil (B)>yellow-brown soil (C)>yellow-cinnamon soil (A)>lateritic red earth (E). The adsorption K(F) and Freundlich exponents n were decreased when temperature was increased from 298 K to 318 K. However, the Gibbs free energy values were found less negative with the increasing temperature. Meanwhile, the extent of diuron adsorption on soil was at rather high level under low pH value conditions and decreased with increasing pH value. In addition, the desorption behavior of diuron in the six soils was in the sequence of lateritic red earth (E)>yellow-cinnamon soil (A)>paddy soil (B)>yellow earth (F)>yellow-brown soil (C)>black soil (D). At the same time, desorption hysteresis of diuron were observed in all of the tested soils. And the soil organic matter content may play an important role in the adsorption-desorption behavior.

Development of a one-step strip for the detection of triazophos residues in environmental samples

Environmental and food safety issues now are recognized internationally, and pesticide residues play key roles as environment and food pollutants. It is crucial to develop methods for rapid determination of pesticide residues in environments and foods. A one-step strip based on nanocolloidal-gold-labeled monoclonal antibodies for detection of triazophos residue was developed. The nanocolloidal gold, with an average particle diameter of 25 nm (G25), was labeled to an antitriazophos monoclonal antibody. This conjugate was dispensed on the conjugate pad of a porous glass fiber. Ovalbumin hapten and goat anti-mouse IgG were dispensed on the nitrocellulose membrane and served as the test line (T-line) and control line (C-line), respectively. After conditions optimization, the one-step strip was finally developed for the residue determination of triazophos. The limit of detection (LOD) of the strip was 4 ng/mL for standard. The detection was not affected by the pH of the liquid sample but low total ion concentration will induce illegible C-line and T-line. The LOD for spiked samples of soil and water was 5ng/mL, with run time of no more than 10min.

Development of a Mab-based heterologous immunoassay for the broad-selective determination of organophosphorus pesticides.

A broad-selective monoclonal antibody (Mab) for organophosphorus (OP) pesticides was raised using heterologous indirect enzyme-linked immunosorbent assay (ELISA) to screen hybridomas. On the basis of this Mab, five coating antigens were used to develop homologous and heterologous indirect competitive ELISAs. With the most suitable competitor, a sensitive and broad-selective ELISA was developed. The IC(50) values were estimated to be 20.32 ng/mL for parathion, 21.44 ng/mL for methyl-parathion, 42.15 ng/mL for fenitrothion, and 58.85 ng/mL for isocarbophos. Spike recoveries were between 70.52 and 103.27% for the detection of single pesticide residues of the four OP pesticides in purple-clayed paddy soil. Moreover, the chosen ELISA was then applied to the detection of mixtures of parathion and methyl-parathion in soil samples. The average recovery and coefficient of variation were 80.91 and 4.82%, respectively. Results proved that this broad-selective ELISA would be useful for the multiresidue determination of OP pesticides.

Development of a direct competitive enzyme-linked immunosorbent assay for parathion residue in food samples.

A heterologous direct competitive enzyme-linked immunosorbent assay (ELISA) for parathion residue determination is described based on a monoclonal antibody and a new competitor. The effects of several physicochemical factors, such as methanol concentration, ionic strength, pH value, and sample matrix, on the performance of the ELISA were optimized for the sake of obtaining a satisfactory assay sensitivity. Results showed that when the assay medium was in the optimized condition (phosphate buffer solution [PBS] containing 10% [v/v] methanol and 0.2 mol/L NaCl at a pH value of 5.0), the sensitivity (estimated as the IC(50) value) and the limit of detection (LOD, estimated as the IC(10) value) were 1.19 and 0.08 ng/ml, respectively. The precision investigation indicated that the intraassay precision values all were below 10% and that the interassay precision values ranged from 4.89 to 19.12%. In addition, the developed ELISA showed a good linear correlation (r(2)=0.9962) to gas chromatography within the analytes concentration range of 0.1 to 16 ng/ml. When applied to the fortified samples (parathion adding level: 5-15 microg/kg), the developed ELISA presented mean recoveries of 127.46, 122.52, 91.92, 124.01, 129.72, 99.37, and 87.17% for tomato, cucumber, banana, apple, orange, pear, and sugarcane, respectively. Results indicated that the established ELISA is a potential tool for parathion residue determination.

Development of a sensitive competitive indirect ELISA for parathion residue in agricultural and environmental samples.

A sensitive competitive indirect enzyme-linked immunosorbent assay (ELISA) for the insecticide parathion was developed. The optimal immunogen was 5-(ethoxy(4-nitrophenoxy)phosphorothioylamino)pentanoic acid. In addition, five competitors were applied for development of a heterologous competitive indirect ELISA. Then several physicochemical factors (organic solvent, ionic strength and pH) that influence assay performance were studied and optimized. The IC(50) and IC(10) of the optimized ELISA were 0.95 and 0.15 ng/mL, respectively, which meant almost 86-fold and 6-fold improvement in the assay sensitivity in comparison with the homologous assay (81.74 ng/mL) and the non-optimized heterologous assay (5.60 ng/mL). Finally, the assay was applied to the analysis of parathion in spiked agricultural and environmental samples without extraction or cleanup. The average recoveries of parathion added to water, soil, cucumber, rice and corn were between 78.57% and 107.67%. The limit of detection (LOD) for water and soil samples was 5 ng/mL, and the LOD for cucumber, rice and corn samples was 10 ng/mL.

Enhanced Competitive Chemiluminescent Enzyme Immunoassay for the Trace Detection of Insecticide Triazophos

A direct competitive chemiluminescent enzyme immunoassay (CLEIA) for triazophos was developed, which was based on the anti-THHe IgG monoclonal antibody and a heterogeneous enzyme tracer (THHu-HRP). Several components of chemiluminescent enhanced solution (CES) were optimized. The results showed that 1 mM of p-iodo-phenol, 0.625 mM of luminol, and 4 mM of H(2)O(2) had the best performance. Based on the study of CES, the influence of several factors (assay buffer, blocking substance, and solvent) on the immunoassay was investigated. The sensitivity for detection, IC(50) value was 0.87 ng/mL at a practical working concentration range between 0.04 ng/mL and 5 ng/mL and the limit of detection for triazophos was 0.063 ng/mL. The average recovery of triazophos added to lettuce, carrot, apple, water, and soil were 78.71%, 67.52%, 118.3%, 117.2%, and 122.0%, respectively. Finally, comparison between the methods of CLEIA and high-performance liquid chromatography-tandem mass spectrum (HPLC-MS/MS) was performed. The results obtained from CLEIA were in agreement with those of HPLC-MS/MS.

Development of a broad-selective immunoassay for multi-residue determination of type II pyrethroids in West Lake water

Abstract With the purpose of finding an immunoassay of similar sensitivity for type II pyrethroids such as fenpropathrin, cypermethrin, deltamethrin, esfenvalerate, cyhalothrin, fluvalinate and flucythrinate, we prepared three kinds of polyclonal antibodies (Pabs), and screened against nine coating antigens (CAgs). The final selected antibody–antigen combination based on heterologous assay was further optimised and tested for tolerance to methanol concentration, ionic strength and pH changes. Sensitivity of optimal immunoassay was found to be quite similar among cypermethrin, deltamethrin and esfenvalerate, as IC50 values were 23.2, 24.5 and 25.1 µg/L for the three pyrethroids, respectively. No cross-reactivity was measured to type I pyrethroids or other relative metabolites. This immunoassay was used to detect different combinations of cypermethrin, deltamethrin and esfenvalerate spiked in West Lake water, and recoveries were between 95.6% and 103.6%, which indicated that the chosen ELISA was feasible for multi-residue analysis.