Synthesis, antiproliferative and 4D-QSAR studies of thiadiazole derivatives bearing acrylamide moiety as EGFR inhibitors

As a target for clinical anti-cancer treatment, epidermal growth factor receptor (EGFR) exhibits its over-expression on various tumour cells and is associated with the development of a variety of human cancers. Herein, we described the synthesis, antiproliferative activity assay and 4D-QSAR studies of thiadiazole derivatives bearing acrylamide moiety as EGFR inhibitors. Compared with Gefitinib, some of the target compounds have excellent antiproliferative activities against EGFR-expressed A431 cell line. The robust and reliable 4D-QSAR was constructed using comparative distribution detection algorithm, ordered predictors selection and genetic algorithm method, and the following acceptable statistics are shown: r² = 0.82, Q²_LOO = 0.67, Q²_LMO = 0.61, r²_Pred = 0.78.

[The progress on post-exposure prophylaxis of tetanus immunological preparation in adults]

The tetanus has been eliminated in the pregnancy women and newborns in China. However, there is a gap for adult tetanus immunization, and the risk of tetanus infection cannot be ignored. In order to clearly understand the effect of the tetanus to human beings and the current use of tetanus immunological preparation for adult post-exposure prophylaxis, the incidence of the tetanus, the use status of tetanus immunological preparation and recommendations for post-exposure prophylaxis at home and abroad were reviewed and summarized, which may provide academic evidence for post-exposure prophylaxis procedures and use of tetanus immunological preparation.

Manipulation of Electrode Composition for Effective Water Management in Fuel Cells Fed with an Electrically Rechargeable Liquid Fuel

The liquid fuel cell, with its high energy density and ease of fuel handling, has attracted great attention worldwide. However, its real application is still being greatly hindered by its limited power density. Hence, the recently proposed and demonstrated fuel cell, using an electrically rechargeable liquid fuel (e-fuel), is believed to be a candidate with great potential due to its significant performance advancement. Unlike the conventional alcoholic liquid fuels, the e-fuel possesses excellent reactivity, even on carbon-based materials, which therefore allows the e-fuel cell to achieve superior performance without any noble metal catalysts. However, it is found that, during the cell operation, the water generated at the cathode following the oxygen reduction reaction could lead to a water flooding problem and further limit the cell performance. To address this issue, in this work, by manipulating the cathode composition, a blended binder cathode using both Nafion and polytetrafluoroethylene as binding agents is fabricated and demonstrated its superiority in the fuel cell to achieve an enhanced water management and cell performance. Furthermore, using the developed cathode, a fuel cell stack is designed and fabricated to power a 3D-printed toy car, presenting this system as a promising device feasible for future study and real applications.

[Hesitancy of parents towards vaccines in national immunization program in three regions in China: a cross-sectional study]

Objective: To investigate the incidence and determinants of vaccine hesitancy towards national immunization program in China and understand the current status of parents' hesitancy to different vaccines used in national immunization program. Methods: A cross-sectional survey was conducted in Beijing, Sichuan and Gansu. The methods of proportional probability sampling and convenience sampling were used to select the eligible study subjects for questionnaire surveys. Results: A total of 3 592 parents were enrolled in the study, in whom 38.22% fully accepted all the vaccines, 59.35% agreed to let their children to receive all the vaccines but showed slight concern, and 2.42% had hesitancy to the vaccines. The vaccine with the most hesitancy was polio vaccine (0.89%), followed by diphtheria pertussis tetanus vaccine (0.70%) and hepatitis A vaccine (0.64%). The dominant reason for vaccine hesitancy was the risk-benefit perception of vaccination (31.03%), followed by the low awareness of the parents (21.84%) and the inconvenience caused by distance and time (21.84%). Conclusions: The incidence of vaccine hesitancy towards national immunization program was low in parents in China, but over 50% of the parents showed concern to the vaccines. It is essential to improve the service quality of national immunization program and strengthen the health education about the vaccination to reduce the incidence of vaccine hesitancy in parents.

[Development and outlook on human challenge trial of vaccine]

Human challenge trial (HCT) is a test in which human volunteers are intentionally infected with pathogens in order to evaluate the efficacy of candidate preventive or therapeutic drugs. During the COVID-19 pandemic, the HCT of vaccines has aroused people's attention due to its significant advantages over clinical trial. This paper introduces the concept, development and application of HCT, the advantages and limitations of HCT for vaccine evaluation, and the consideration of future HCT of COVID-19 vaccine in China.

[Review on immunogenicity, safety and social value of combined vaccines for children used both at home and abroad]

Combined vaccines contain two or more antigens. Research suggested that combined vaccines could prevent multi diseases and reduce the frequency of vaccination. This article focus on combined vaccines for children used both at home and abroad, such as diphtheria-pertussis-tetanus vaccine (DTaP), measles-rubella-mumps vaccine (MMR), etc. and summarizes their immunogenicity, safety and social values, including benefits to families, vaccination workers and health services, to provide evidence for promoting the research, development and use of combined vaccines in China. We found that combined vaccines can not only ensure the immunogenicity and safety, but also give convenient and lower cost vaccination to families, and using combined vaccines can improve the work efficiency of vaccination workers, reduce the impact of the epidemic on immunization services and improve vaccination coverage and timeliness. At present, the promotion of combined vaccines in China is restricted by many technical bottlenecks, high prices, and low awareness among people. It is recommended that research on the safety, effectiveness and health economics of combined vaccines should be strengthened, and the value of combined vaccines should be scientifically evaluated; the public's awareness and trust in combined vaccines should be enhanced, as well as the development and application of multi-linked multivalent vaccines should be promoted. The government should improve regulations to assist the development and application of combined vaccines.

Synthesis and receptor dependent 4D-QSAR studies of 4,5-dihydro-1,3,4-oxadiazole derivatives targeting cannabinoid receptor

Cannabinoid receptor has been shown to be overexpressed in various types of cancers, especially non-small cell lung cancer. As a result, it could be used as novel target for anticancer treatments. Because receptor-dependent 4D-QSAR generates conformational ensemble profiles of compounds by molecular dynamics simulations at the binding site of the enzyme, this work describes the synthesis, biological activity evaluation and 4D-QSAR studies of 4,5-dihydro-1,3,4-oxadiazole derivatives targeting cannabinoid receptor. Compared with WIN55,212-2, compound 5 f showed the best antiproliferative activity. The receptor-dependent 4D-QSAR model was generated by multiple linear regression method using QSARINS. Leave-n-out cross-validation and chemical applicability domain were performed to analyse the independent test set and to verify the robustness of the model. The best 4D-QSAR model showed the following statistics: r² = 0.8487, Q²_LOO = 0.7667, Q²_LNO = 0.7524, and r²_Pred = 0.8358.

On-Site Fluorination for Enhancing Utilization of Lithium in a Lithium-Sulfur Full Battery

The rechargeability of the lithium anode in lithium-sulfur (Li-S) batteries is an issue for this type of battery. In this work, we demonstrate a Li-S full battery comprising a protected anode scaffold and a Li₂S cathode. The stabilized performance is attained by an on-site fluorination strategy, using BiF₃ for the interfacial coating of the anode. Unlike previously reported LiF protective coating derived from the vapor/solution depositions, BiF₃ nanocrystals would be lithiated on-site to the anode surface and server as the protective layer. The chemically inertial Li₃Bi alloy can provide additional ion-conductive paths and stitch the LiF to form a seamless protective layer, thereby suppressing the dendrite propagation and parasitic reactions effectively. With the designed anode structures and compositions, the high-loading full battery (8.05 mg cm^-2) can achieve an exceptional utilization of both sulfur (898 mAh g_S^-1) and lithium (1533 mAh g_Li^-1) over 200 cycles, marking a step toward cyclable Li metal batteries at a high capacity.

Rational design of spontaneous reactions for protecting porous lithium electrodes in lithium-sulfur batteries

A rechargeable lithium anode requires a porous structure for a high capacity, and a stable electrode/electrolyte interface against dendrite formation and polysulfide crossover when used in a lithium-sulfur battery. Here, we design two simple steps of spontaneous reactions for protecting porous lithium electrodes. First, a reaction between molten lithium and sulfur-impregnated carbon nanofiber forms a fibrous network with a lithium shell and a carbon core. Second, we coat the surface of this porous lithium electrode with a composite of lithium bismuth alloys and lithium fluoride through another spontaneous reaction between lithium and bismuth trifluoride, solvated with phosphorous pentasulfide, which also polymerizes with lithium sulfide residual in the electrode to form a solid electrolyte layer. This protected porous lithium electrode enables stable operation of a lithium-sulfur battery with a sulfur loading of 10.2 mg cm-2 at 6.0 mA cm-2 for 200 cycles.

Establishment and characterization of a chimeric infectious cDNA clone of classical swine fever virus

Classical swine fever virus (CSFV) causes a highly contagious disease among swine that has an important economic impact worldwide. There are two important CSFV strains in China, Shimen and hog cholera lapinized virus (HCLV). Shimen strain is highly virulent while HCLV, also referred to as C-strain, is a live attenuated vaccine strain considered to be one of the most effective and safest live vaccines. In this study, a chimeric infectious cDNA clone of CSFV named pT7SM-c was engineered by replacing the E(rns) genomic region of an infectious clone of CSFV Shimen strain, pT7SM, with the same region obtained from HCLV. RNA transcripts of pT7SM-c containing an engineered EcoRI site that served as a genetic marker were directly infectious in PK15 cells. The rescued virus vT7SM-c showed similar growth kinetics and cytopathic effect with the parental virus vT7SM in the cells. The chimeric infectious cDNA clone can be used as a practical tool for further studying of the virulence, protein function and pathogenesis of CSFV through genetic manipulation.

Inhibition of human positive cofactor 4 radiosensitizes human esophageal squmaous cell carcinoma cells by suppressing XLF-mediated nonhomologous end joining

Radiotherapy has the widest application to esophageal squamous cell carcinoma (ESCC) patients. Factors associated with DNA damage repair have been shown to function in cell radiosensitivity. Human positive cofactor 4 (PC4) has a role in nonhomologous end joining (NHEJ) and is involved in DNA damage repair. However, the clinical significance and biological role of PC4 in cancer progression and cancer cellular responses to chemoradiotherapy (CRT) remain largely unknown. The aim of the present study was to investigate the potential roles of PC4 in the radiosensitivity of ESCC. In this study, we showed that knockdown of PC4 substantially increased ESCC cell sensitivity to ionizing radiation (IR) both in vitro and in vivo and enhanced radiation-induced apoptosis and mitotic catastrophe (MC). Importantly, we demonstrated that silencing of PC4 suppressed NHEJ by downregulating the expression of XLF in ESCC cells, whereas reconstituting the expression of XLF protein in the PC4-knockdown ESCC cells restored NHEJ activity and radioresistance. Moreover, high expression of PC4 positively correlated with ESCC resistance to CRT and was an independent predictor for short disease-specific survival of ESCC patients in both of our cohorts. These findings suggest that PC4 protects ESCC cells from IR-induced death by enhancing the NHEJ-promoting activity of XLF and could be used as a novel radiosensitivity predictor and a promising therapeutic target for ESCCs.

Nonequilibrium scheme for computing the flux of the convection-diffusion equation in the framework of the lattice Boltzmann method

In this paper, we propose a local nonequilibrium scheme for computing the flux of the convection-diffusion equation with a source term in the framework of the multiple-relaxation-time (MRT) lattice Boltzmann method (LBM). Both the Chapman-Enskog analysis and the numerical results show that, at the diffusive scaling, the present nonequilibrium scheme has a second-order convergence rate in space. A comparison between the nonequilibrium scheme and the conventional second-order central-difference scheme indicates that, although both schemes have a second-order convergence rate in space, the present nonequilibrium scheme is more accurate than the central-difference scheme. In addition, the flux computation rendered by the present scheme also preserves the parallel computation feature of the LBM, making the scheme more efficient than conventional finite-difference schemes in the study of large-scale problems. Finally, a comparison between the single-relaxation-time model and the MRT model is also conducted, and the results show that the MRT model is more accurate than the single-relaxation-time model, both in solving the convection-diffusion equation and in computing the flux.

Lattice Boltzmann model for the convection-diffusion equation

We propose a lattice Boltzmann (LB) model for the convection-diffusion equation (CDE) and show that the CDE can be recovered correctly from the model by the Chapman-Enskog analysis. The most striking feature of the present LB model is that it enables the collision process to be implemented locally, making it possible to retain the advantage of the lattice Boltzmann method in the study of the heat and mass transfer in complex geometries. A local scheme for computing the heat and mass fluxes is then proposed to replace conventional nonlocal finite-difference schemes. We further validate the present model and the local scheme for computing the flux against analytical solutions to several classical problems, and we show that both the model for the CDE and the computational scheme for the flux have a second-order convergence rate in space. It is also demonstrated the present model is more accurate than existing LB models for the CDE.

Effect of the forcing term in the multiple-relaxation-time lattice Boltzmann equation on the shear stress or the strain rate tensor

In this work, the effect of the forcing term (or external force) in the multiple-relaxation-time lattice Boltzmann equation (MRTLBE) on the shear stress or the strain rate tensor is studied theoretically and numerically. Through a Chapman-Enskog analysis and numerical simulations, we show that the shear stress (or the strain rate tensor) derived from the MRTLBE is second-order accurate in space. We then examine the influence of the forcing term on the shear stress or the strain rate tensor, and demonstrate that the forcing term effect must be included when the shear stress or the strain rate tensor is computed with the nonequilibrium part of the distribution function.

Discrete effects on boundary conditions for the lattice Boltzmann equation in simulating microscale gas flows

The lattice Boltzmann equation (LBE) has shown its promise in the simulation of microscale gas flows. One of the critical issues with this advanced method is to specify suitable slip boundary conditions to ensure simulation accuracy. In this paper we study two widely used kinetic boundary conditions in the LBE: the combination of the bounce-back and specular-reflection scheme and the discrete Maxwell's scheme. We show that (i) both schemes are virtually equivalent in principle, and (ii) there exist discrete effects in both schemes. A strategy is then proposed to adjust the parameters in the two kinetic boundary conditions such that an accurate slip boundary condition can be implemented. The numerical results demonstrate that the corrected boundary conditions are robust and reliable.

Lattice Boltzmann simulation of dense gas flows in microchannels

It is true that the Knudsen number that characterizes gas flows in microchannels increases to a finite value as the geometric dimension is reduced. However, since the gas in such a flow may retain a small mean free path and a small mean molecular spacing, the gas can still be rather dense in microdevices. Gas flows in microchannels have mainly been studied by molecular dynamics and direct simulation Monte Carlo methods. However, both methods are computationally expensive. In this work, we study dense gas flows in microchannels using an Enskog equation-based lattice Boltzmann Bhatnagar-Gross-Krook model. It is found that a dense gas flowing through a microchannel behaves different than a dilute gas under the same flow conditions.

Thermal lattice Boltzmann equation for low Mach number flows: decoupling model

A lattice Boltzmann model is proposed for solving low Mach number thermal flows with viscous dissipation and compression work in the double-distribution-function framework. A distribution function representing the total energy is defined based on a single velocity distribution function, and its evolution equation is derived from the continuous Boltzmann equation. A lattice Boltzmann equation model with clear physics and a simple structure is then obtained from a kinetic model for the decoupled hydrodynamic and energy equations. The model is tested by simulating a thermal Poiseuille flow and natural convection in a square cavity, and it is found that the numerical results agree well with the analytical solutions and/or the data reported in previous studies.

Multiwalled Carbon Nanotube Supported PtRu for the Anode of Direct Methanol Fuel Cells

The activity of the methanol oxidation reaction of a multiwalled carbon nanotube (MWCNT)-supported PtRu catalyst was investigated and compared with the Vulcan XC-72 carbon-supported catalyst. The PtRu nanoparticles with 1:1 and 7:3 atomic ratios (with similar PtRu loadings and morphological structures) were deposited both on the MWCNTs and on the carbon. Cyclicvoltammetry results demonstrated that the MWCNT-supported PtRu catalyst exhibited a higher mass activity (mA mg(-1) of PtRu) for the methanol oxidation reaction than the carbon-supported PtRu under the condition that both catalysts possess more or less the same PtRu loadings, particle sizes, dispersions, and electrochemical surface area. The direct methanol fuel cell performance test data showed that MWCNT-supported PtRu catalysts yielded about 35-39% higher power densities than the carbon-supported PtRu.

Lattice Boltzmann method for incompressible flows with large pressure gradients

Conventional lattice Boltzmann Bhatnagar-Gross-Krook (LBGK) models can simulate incompressible flows correctly only if the Mach number M and the density variation deltarho are negligibly small. However, the equation of state p=RTrho resulting from the conventional models limits their application to incompressible flows with a rather small pressure gradient. In this paper, based on the Enskog equation, we propose a finite difference lattice BGK model for isothermal incompressible flows with the resulting equation of state and transport properties suitable for nonideal fluids. We validated this model by simulating the plane Poiseuille flow, the two dimensional Womersley flow, and the backward-facing step flow and found that the numerical results obtained by the proposed model are more accurate than those by the conventional LBGK models when the pressure gradient imposed on the flows increases.

Temperature dependence of the velocity boundary condition for nanoscale fluid flows

Velocity slips may occur as a fluid flows over a solid surface in the nanometer scale. The slip length L(s) , characterizing the degree of slip, is usually used to describe the velocity boundary condition at the fluid/solid interface. In this work, we show that for a given wall-fluid system, the slip length L(s) generally varies with the system temperature T . In particular, we show that it is possible to create a pair of solid wall and fluid systems, in which the velocity slip becomes rather small and independent of temperature.

A lattice Boltzmann algorithm for electro-osmotic flows in microfluidic devices

In this paper, a finite-difference-based lattice Boltzmann (LB) algorithm is proposed to simulate electro-osmotic flows (EOF) with the effect of Joule heating. This new algorithm enables a nonuniform mesh to be adapted, which is desirable for handling the extremely thin electrical double layer in EOF. The LB algorithm has been validated by simulating a problem with an available analytical solution and it is found that the numerical results predicted by the algorithm are in good agreement with the analytical solution. The LB algorithm is also applied to modeling a mixed electro-osmotic/pressure driven flow in a channel. The numerical results show that Joule heating plays an important role in EOF.

Simple kinetic model for fluid flows in the nanometer scale

Fluid flows in the nanometer scale can be studied by molecular dynamics or Monte Carlo methods, but the time and length scales are usually limited to rather short ranges due to the computational expense. Kinetic theory is an alternative tool for studying nanoscale flows, but the existing models are rather complicated and difficult to implement. In this paper, we propose a simple Enskog-like kinetic model for nanoscale flows. The results predicted by this model compare well with molecular dynamics or Monte Carlo simulation results in the literature.

Finite-difference-based lattice Boltzmann model for dense binary mixtures

We propose a finite-difference-based lattice Boltzmann model for dense binary mixtures based on the Enskog theory. The model is applicable to a mixture composed of two dense fluids with different shear viscosities. The macroscopic hydrodynamic and diffusion equations are derived from the model through the Chapmann-Enskog procedure. The model is also validated numerically.

Thermal lattice Bhatnagar-Gross-Krook model for flows with viscous heat dissipation in the incompressible limit

In this paper, by introducing a different distribution function and starting from the Boltzmann equation as well as the Maxwell-Boltzmann distribution, we obtain a Boltzmann Bhatnagar-Gross-Krook (BGK) equation for thermal flows with viscous heat dissipation in the incompressible limit. The continuous thermal BGK model is then discretized over both time and phase space to form a lattice BGK model, which is shown to be consistent with some existing double distribution function lattice BGK models based on macroscopic governing equations. We have also demonstrated that the lattice BGK model derived theoretically in this work can be used to simulate laminar incompressible convention heat transfer with/without viscous heat dissipation.

Preconditioned lattice-Boltzmann method for steady flows

In this paper we propose a preconditioned lattice Boltzmann (LB) method for steady incompressible flows. For steady flows, the macroscopic equations derived from this LB model are equivalent to those from the standard LB model, but with an improved eigenvalue system. The proposed model can be viewed as an explicit solver for preconditioned compressible Navier-Stokes equations. Linear stability analysis is performed and the results show that the stability of the model is the same as that of the standard LB model for low Mach numbers. The proposed model retains the structure of the standard LB model and, hence, possesses all the advantages. Numerical tests show that the convergence rate can be enhanced as much as an order of magnitude compared to the standard lattice Boltzmann method. The accuracy of the solutions is improved as well.

Discrete velocity and lattice Boltzmann models for binary mixtures of nonideal fluids

In this paper, a discrete velocity model and a lattice Boltzmann model are proposed for binary mixtures of nonideal fluids based on the Enskog theory. The velocity space of the Enskog equation for each component is first discretized by applying a Gaussian quadrature, resulting in a discrete velocity model that can be solved by suitable numerical schemes. A lattice Boltzmann model is then derived from the discrete velocity model with a slightly modified equilibrium. The hydrodynamics of each model are also derived through the Chapmann-Enskog procedure.

Explicit finite-difference lattice Boltzmann method for curvilinear coordinates

In this paper a finite-difference-based lattice Boltzmann method for curvilinear coordinates is proposed in order to improve the computational efficiency and numerical stability of a recent method [R. Mei and W. Shyy, J. Comput. Phys. 143, 426 (1998)] in which the collision term of the Boltzmann Bhatnagar-Gross-Krook equation for discrete velocities is treated implicitly. In the present method, the implicitness of the numerical scheme is removed by introducing a distribution function different from that being used currently. As a result, an explicit finite-difference lattice Boltzmann method for curvilinear coordinates is obtained. The scheme is applied to a two-dimensional Poiseuille flow, an unsteady Couette flow, a lid-driven cavity flow, and a steady flow around a circular cylinder. The numerical results are in good agreement with the results of previous studies. Extensions to other lattice Boltzmann models based on nonuniform meshes are also discussed.

Lattice Boltzmann model for incompressible flows through porous media

In this paper a lattice Boltzmann model is proposed for isothermal incompressible flow in porous media. The key point is to include the porosity into the equilibrium distribution, and add a force term to the evolution equation to account for the linear and nonlinear drag forces of the medium (the Darcy's term and the Forcheimer's term). Through the Chapman-Enskog procedure, the generalized Navier-Stokes equations for incompressible flow in porous media are derived from the present lattice Boltzmann model. The generalized two-dimensional Poiseuille flow, Couette flow, and lid-driven cavity flow are simulated using the present model. It is found the numerical results agree well with the analytical and/or the finite-difference solutions.

Modification of AOAC multiresidue method for determination of synthetic pyrethroid residues in fruits, vegetables, and grains. Part I: Acetonitrile extraction system and optimization of florisil cleanup and gas chromatography

We present a multiresidue method for determination of synthetic pyrethroids in fruits, vegetables, and grains. The method is a modification of AOAC Method 970.52. Residues are extracted with acetonitrile (for fruits and vegetables) or acetonitrile-water (2 + 1) (for grains) and then transferred to hexane. Coextractives are removed by acetonitrile partitioning and open-column chromatography with deactivated Florisil. The final extract is analyzed by gas chromatography with electron capture detection (GC-ECD). An HP-17 wide-bore column is used to determine the individual isomeric contents of each insecticide. The method was used to recover 8 pyrethroids (biphenthrin, fenpropathrin, cyhalothrin, permethrin, cypermethrin, fluvalinate, fenvalerate, and deltamethrin) spiked at 0.01-4.0 mg/kg in 20 crops (apple, pear, peach, banana, grape, strawberry, potato, tomato, cucumber, pepper, cabbage, carrot, celery, polished rice, wheat, green gram, buckwheat, sorghum, maize, and barley). Recoveries of the 8 pyrethroid insecticides in 6 crops ranged from 83.8 to 112.8%, with a coefficient of variation (CV) of 2.00 to 12.09% for the narrow-bore capillary GC (n = 6) and from 82.8 to 106.4%, CV = 2.93-12.19%, for the wide-bore capillary GC (n = 6). The minimum detectable levels of 0.004-0.028 mg/kg (for fruits and vegetables) or 0.01-0.08 mg/kg (for grains) for the 8 pyrethroids are easy to detect.

Modification of AOAC multiresidue method for determination of synthetic pyrethroid residues in fruits, vegetables, and grains. Part II: Acetone extraction system

To optimize conditions and to evaluate further a multiresidue method for pyrethroids, various extraction solvents and partitioning conditions were examined. Acetone and acetonitrile (for fruits and vegetables) and acetone-water and acetonitrile-water (for grains) were used as solvents with or without acetonitrile partitioning. Twenty crops fortified with 8 pyrethroid insecticides at low, medium, and high levels were analyzed. For limit of detection (LOD) levels, repeatability tests were completed with acetone-water as extraction solvent. Recoveries of 8 pyrethroid insecticides at LOD levels were 76.2-99.6%, with coefficients of variation (CVs) of 2.08-10.90% for narrow-bore capillary gas chromatography (GC) (n = 6) and 80.1-107.3% with CVs of 3.76-15.38% for wide-bore capillary GC (n = 6). Both acetone or acetone-water extraction with acetonitrile partitioning and acetonitrile or acetonitrile-water extraction with acetonitrile partitioning are suitable for multiresidue analysis of pyrethroid insecticides. However, acetonitrile and acetonitrile-water as extraction solvents were better than acetone and acetone-water at LOD-fortified levels. This finding was confirmed chromatographically with pear, cucumber, and barley control samples.

Cleanup with two Florisil columns for gas chromatographic determination of multiple pyrethroid insecticides in products of animal origin

A gas chromatographic method was developed for the simultaneous determination of 9 pyrethroid insecticides in products of animal origin. The multiresidues of the pyrethroids in different samples were extracted with acetone-petroleum ether (1 + 1), and extracts were cleaned up on a Florisil partition column and a Florisil adsorption column. Four animal tissue samples were examined at 0.05-0.25 ppm fortification levels. The average recoveries of all insecticides were 76.9-88.0%, and the coefficients of variation were < 4.6% for all insecticides except permethrin. The detection limits of the method were ca 5 ppb for all insecticides but permethrin, which had a detection limit of ca 10 ppb.

Packed-column gas chromatographic method for the simultaneous determination of 10 pyrethroid insecticide residues in fruits, vegetables, and grains

A simple, rapid, packed-column gas chromatographic method was developed for simultaneous determination of 10 pyrethroid insecticide residues (allethrin, biphenthrin, cyhalothrin, permethrin, cyfluthrin, flucythrinate, fenvalerate, fluvalinate, deltamethrin, and py-115) in fruits, vegetables, and grains. These multiresidues are extracted from various crops with acetone-petroleum ether and cleaned up on a Florisil column (for the fruits and vegetables) or on a Florisil-charcoal-alumina column (for the grains) prior to their determination by gas chromatography with an electron capture detector. Recoveries of 10 pyrethroid compounds from 12 different crops (maize, soybeans, wheat, sorghums, paddy, potatoes, cucumbers, cauliflowers, spinaches, apples, bananas, and oranges) fortified at levels of 0.02-5.00 ppm ranged from 58 to 130%. In a separate precision study, coefficients of variation were 5.5-14.6% at 0.1-0.5 ppm (n = 10, maize), and 4.1-12.1% at 0.010-0.050 ppm (n = 10, apples). The detection limits of the method ranged from 2.0 to 10.0 ppb on a crop basis.

Rapid method for the determination of multiple pyrethroid residues in fruits and vegetables by capillary column gas chromatography

A rapid and economical simplified multi-residue method is described for the determination of multiple pyrethroid insecticides in fruits and vegetables. The residues are extracted from crops with methanol and the crop co-extractives are removed by toluene partitioning and Florisil-charcoal minicolumn chromatography. The final extract is analysed by capillary column gas chromatography with electron-capture detection. The recoveries were determined by fortifying six different crops (apples, oranges, cabbages, pears, peppers and tomatoes) with eleven pyrethroids (Py-115, allethrin, biphenthrin, fenpropathrin, cyhalothrin, permethrin, cyfluthrin, flucythrinate, fluvalinate, fenvalerate and deltamethrin) at three levels, 0.01-0.07, 0.10-0.70 and 1.0-7.0 mg/kg. Three determinations were made at each level for each crop. Recoveries of the eleven pyrethroids ranged from 70.4 to 110.0% at the three different levels. The practical determination limit of the method was in the range 3.0-30.0 micrograms/kg for all the pyrethroid insecticides. The proposed method had major advantages that simplified steps were achieved for the extraction and the clean-up, the solvent consumption was reduced and the analysis time was shortened.