Deguang Li

Preparation and characterization of 1-naphthylacetic acid?silica conjugated nanospheres for enhancement of controlled-release performance

Chemical pesticides have been widely used to increase the yield and quality of agricultural products as they are efficient, effective, and easy to apply. However, the rapid degradation and low utilization ratio of conventional pesticides has led to environmental pollution and resource waste. Nano-sized controlled-release formulations (CRFs) can provide better penetration through the plant cuticle and deliver the active ingredients efficiently to the targeted tissue. In this paper we reported novel conjugated nanospheres derived from 1-naphthylacetic acid (NNA), 3-aminopropyltriethoxysilane (APTES) and tetraethyl orthosilicate and their application as a controlled-release plant growth regulator. The NNA and APTES conjugate was prepared through a covalent cross-linking reaction and subsequent hydrolyzation and polycondensation to synthesize NNA-silica nanospheres. The release data indicated that the release of NNA was by non-Fickian transport and increased as particle size decreased. It was also found that the acidity-alkalinity was enhanced and as the temperature increased, the release of the active ingredient was faster. The nanoconjugate displayed a better efficacy in promoting root formation than NNA technical. The present study provides a novel synthesis route for CRFs comprising a pesticide, with long-duration sustained-release performance and good environmental compatibility. This method may be extended to other pesticides that possess a carboxyl group.

Preparation and characterization of double-shelled avermectin microcapsules based on copolymer matrix of silica–glutaraldehyde–chitosan

Controlled release formulation (CRF) of pesticides is highly desirable for attaining the most effective utilization of the pesticide as well as reducing environmental pollution. Due to the selective permeation and protection properties of the semi-permeable membrane, pesticide microcapsules have been widely used. In this work, we developed a novel two-step method for synthesizing highly stable silica-glutaraldehyde-chitosan composite avermectin microcapsules. The silica shell was formed through the hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) at the oil droplet-water interface by using TEOS as the silica precursor and hexadecyl trimethyl ammonium chloride as a surfactant. Then the silica shell was modified with 3-aminopropyltriethoxysilane. Chitosan nanospheres were prepared by adjusting the pH value of the solution and then cross-linking with modified silica at the surface of the silica shell in the presence of glutaraldehyde to form double-shelled avermectin microcapsules. The results showed that the resulting microcapsules had a remarkable loading ability for avermectin (about 40% w/w) and can protect avermectin against photo- and thermal degradation effectively. Compared to single-shelled microcapsules, the double-shelled ones had better controlled release properties under all conditions. The present study provides a novel CRF comprising a pesticide which is light-sensitive or high temperature-sensitive, and a method for preparing the improved pesticide formulation so that the pesticide release rate and release period could be adjusted.

Determination of malondialdehyde in biological fluids by high-performance liquid chromatography using rhodamine B hydrazide as the derivatization reagent

Malondialdehyde (MDA) is a biomarker for lipid peroxidation, and studies of sensitive and selective analytical methods for it are very important for pathological research. The aim of this work was to develop and validate a novel HPLC method for the quantification of MDA in biological fluids using rhodamine B hydrazide (RBH) as the derivatization reagent. After pretreatment and derivatization in acid medium at 50 °C for 40 min, the RBH-derivatized MDA was separated on a Kromasil C18 column at 25 °C and detected by a fluorescence detector at excitation wavelength of 560 nm and emission wavelength of 580 nm. The results showed linearity in the range of 0.8-1500.0 nM with a detection limit of 0.25 nM (S/N = 3). The recovery of MDA from plasma and urine was 91.50 to 99.20%, with a relative standard deviation range of 1.45 to 3.26%. In comparison to other methods reported for the determination of MDA, the proposed method showed superiority in simplicity, more sensitivity, shorter derivatization time, and less interference. The developed method was applied to quantification of MDA in human biological fluids collected from five volunteers with a concentration range of 24.62-245.00 nM.

Development and validation of a high-performance liquid chromatography method for determination of ractopamine residue in pork samples by solid phase extraction and pre-column derivatization.

Ractopamine (RAC) has been approved as a feed additive for swine, cattle or turkey, and is likely to have residue in edible animal products and may pose a potential risk for consumer health. Therefore, it is essential to establish a method to detect the residue of RAC in animal products. This work presents a rapid and sensitive HPLC method for the determination of RAC in pork samples with pre-column derivatization. The RAC derivative was separated on a kromasil C18 column and detected at 284nm with a UV detector. The detection capability (CCβ) was 0.078μgg(-1) and the linearity was established over the concentration range of 0.15-100.0μgg(-1). The overall mean recovery in spike range of 0.2μgg(-1) to 100μgg(-1) was 89.9% with the overall mean relative standard deviation of 4.1%. This method can be used for the quantification of RAC in pork samples and help to establish adequate monitoring of the residue of RAC.

Adsorption properties and degradation dynamics of endocrine-disrupting chemical levonorgestrel in soils.

Levonorgestrel, a synthetic progesterone used as an oral contraceptive or emergency contraceptive pill, has been shown to be an endocrine-disrupting chemical. To assess the environmental risk of levonorgestrel, batch experiments and laboratory microcosm studies were conducted to investigate the adsorption and degradation of levonorgestrel in five contrasting soils of China. Freundlich and Langmuir models were applied to sorption data to examine the affinity of levonorgestrel for soils with varying physical and chemical properties. The K(f) of levonorgestrel in the tested soils ranged from 10.79 to 60.92 mg(1-n) L(n) kg(-1) with N between 0.69 and 1.23, and the Q(m) ranged from 18.18 to 196.08 mg/kg. The multiple regression analysis was conducted between K(f) and soil properties. Results indicate that total organic carbon plays a dominant role in the adsorption process. Gibbs free energy values less than 40 kJ/mol demonstrate that levonorgestrel sorption on soils could be considered as a physical adsorption. The degradation of levonorgestrel in five soils was fitted by the first-order reaction kinetics model. The half-lives of levonorgestrel were between 4.32 and 11.55 days. The initial concentration and sterilization experiments illustrated that the degradation rate of levonorgestrel in soil was concentration-dependent and microbially mediated. The low mobility potential of levonorgestrel in soils was predicted by the groundwater ubiquity score (GUS) and retardation factor (R(f)).

Determination and dynamics of kanamycin A residue in soil by HPLC with SPE and precolumn derivatization

As one of the aminoglycoside antibiotics, kanamycin has been widely used in human therapy and as an additive to promote growth and prevent disease in forage. The kanamycin residue may have potenital risks for organisms and the environment. Therefore, the monitoring of this drug may have dynamic importance. In this work, a novel method for determination and dynamic study of kanamycin A was developed through solid phase extraction and derivatization with 4-chloro-3,5-dinitrobenzotrifluoride before high-performance liquid chromatography analysis. The calculated recoveries were from 72.3 to 92.5%, with relative standard deviations from 2.99 to 6.94%. The detection limit of kanamycin A in soil was 0.006 mg kg−1 with a signal-to-noise ratio of 3. The dynamics in soil showed that the degradation of kanamycin A coincided with the equations C = 1.951e−0.0482 t for black soil and C = 1.807 e−0.0247 t for red soil and the half-lives were 14.38 and 28.06 d respectively. The degradation rate reached 95.19% in black soil after 63 days compared with 77.14% in red soil.