Simultaneous Determination of Rimsulfuron and Haloxyfop-P-methyl and Its Metabolite Haloxyfop in Tobacco Leaf by LC-MS/MS.

Background: Tobacco (Nicotiana tabacum L.), is an important economic crop. In China, the use of rimsulfuron and haloxyfop-P-methyl herbicides for weed management during the planting period is necessary to improve the production of tobacco. Objective: To establish and validate a quick, easy, cheap, effective, rugged, and safe LC-MS/MS method to determine rimsulfuron, haloxyfop-P-methyl, and haloxyfop in tobacco leaf samples. Methods: We optimized MS/MS conditions and chromatographic conditions for optimal detection conditions. The extraction solvent and sorbent were optimized, and the analysis of variance was applied to analyze the pretreatment method to obtain the optimal pretreatment conditions. Results: The validation results showed that the proposed method exhibited good linearity (R² > 0.9978), satisfactory recovery (72.51-101.60%) and low LOQ (0.02-1.00 mg/kg). The matrix effects of the three analytes in the two tobacco leaf matrixes were different. The dissipation results showed that the half-lives of rimsulfuron and haloxyfop-P-methyl in fresh tobacco leaf samples were ranged from 2.4 to 3.7 days. The final residues of rimsulfuron, haloxyfop-P-methyl, and haloxyfop in flue-cured tobacco leaf samples were all lower than the LOQ. Conclusions: The results demonstrate that the developed method could be used to detect rimsulfuron, haloxyfop-P-methyl, and haloxyfop in tobacco leaf matrixes. Highlights: A method for simultaneous determination of rimsulfuron, haloxyfop-P-methyl, and haloxyfop in tobacco leaf samples with high sensitivity has been established for the first time.

Dissipation, residues, and risk assessment of imidacloprid in Zizania latifolia and purple sweet potato under field conditions using LC-MS/MS.

A shortened version of Quick, Easy, Cheap, Effective, Rugged, and Safe method (QuEChERS) for determining the dissipation and residue of imidacloprid present in Zizania latifolia and purple sweet potato was established by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The average recoveries of imidacloprid in the two crops ranged from 82.12 to 113.79%, with relative standard deviation (RSD) of <7.32%. The dissipation dynamics of imidacloprid in Z. latifolia plants and purple sweet potato plants followed first-order kinetics, with half-lives of 3.2-5.5 days in each of sampling locations. The terminal imidacloprid residues in Z. latifolia and purple sweet potato at each of location were <0.005-0.120 mg kg-1. According to the risk assessment results, both the acute dietary risk quotient and chronic dietary risk quotient values were <1, indicating that imidacloprid is unlikely to pose health risks to humans with normal recommended use. The present study may serve as a valuable reference for the safe and reasonable use of imidacloprid in Z. latifolia and purple sweet potato fields.

Residues, dissipation kinetics, and dietary intake risk assessment of two fungicides in grape and soil.

The residue behavior and dietary intake risk of two fungicides (dimethomorph and pyraclostrobin) in grape (Vitis vinifera L.) were investigated from field trials. A modified quick, easy, cheap, effective, rugged, and safe method for simultaneously determining dimethomorph and pyraclostrobin residues in grape and soil was established using high performance liquid chromatography-tandem mass spectrometry. The average recoveries of dimethomorph and pyraclostrobin in the grape and soil matrices varied from 76.88% to 97.05%, with relative standard deviations of 1.73%-10.38%. The degradation half-lives of dimethomorph and pyraclostrobin were 7.3-12.0 days and 3.6-7.0 days in grape and soil, respectively. The terminal residues of dimethomorph and pyraclostrobin in the two matrices were 0.05-0.87 mg/kg. For dietary exposure risk assessments, all of the hazard quotient and hazard quotient index values were below 100%, which indicated that the suspending agents of dimethomorph and pyraclostrobin were sprayed on grape at the recommended dosages with no significant potential risks for Chinese consumers. This study provides a reference for analytically evaluating residual degradation behavior and dietary intake risk of two fungicides under field conditions.

Simultaneous determination of residues of thiamethoxam and its metabolite clothianidin in tobacco leaf and soil using liquid chromatography-tandem mass spectrometry.

A simple analytical method was developed to simultaneously determine thiamethoxam and its metabolite, clothianidin, in fresh tobacco leaf, soil and cured tobacco leaf using liquid chromatography with tandem mass spectrometry. Thiamethoxam and clothianidin in tobacco and soil samples were extracted with acetonitrile containing 0.1% formic acid and purified using an NH2 -SPE column. The optimized method provided good linearity with coefficients of determination R2 ≥ 0.9981. The limits of detection and quantification were between 0.006-0.12 and 0.02-0.4 mg/kg, respectively. Intra- and inter-day recovery assays were used to validate the established method. The average recoveries of thiamethoxam and clothianidin in fresh tobacco leaf, soil and cured tobacco leaf were 75.04-100.47%, 75.86-86.40% and 89.83-99.39%, respectively. The intra- and inter-day relative standard deviations were all <9%. The developed method was successfully applied for the analysis of thiamethoxam and clothianidin residues in actual tobacco and soil samples. The results indicated that the established method met the requirements for the analysis of trace amounts of thiamethoxam and clothianidin in fresh tobacco leaf, soil and cured tobacco leaf.

Dissipation, residues and risk assessment of spirotetramat and its four metabolites in citrus and soil under field conditions by LC-MS/MS.

A modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method for the simultaneous determination of spirotetramat and its four metabolite residues in citrus, peel, pulp and soil was developed and validated by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The samples were extracted with acetonitrile (1%, glacial acetic acid, v/v) and purified using primary secondary amine and octadecylsilane. The limit of detection was 0.01-0.13 mg/kg, whereas that of quantification was 0.02-0.40 mg/kg for spirotetramat and its metabolites. The average recoveries of spirotetramat, spirotetramat-enol, spirotetramat-mono-hydroxy, spirotetramat-enol-glucoside and spirotetramat-ketohydroxy in all matrices were 73.33-107.91%, 75.93-114.85%, 76.44-100.78%, 71.46-103.19% and 73.08-105.27%, respectively, with relative standard deviations < 12.32%. The dissipation dynamics of spirotetramat in citrus and soil followed first-order kinetics, with half-lives of 2.3-8.5 days in the three sampling locations. The terminal residues of spirotetramat in four matrices at the three locations were measured below the 1.0 mg/kg maximum residue limit set by China, and residues were found to be concentrated on the peel. The risk assessment of citrus was evaluated using risk quotients. The risk quotient values were found to be significantly <1, suggesting that the risk to human health was negligible when using the recommended doses of spirotetramat in citrus. These results could provide guidance for the safe and proper application of spirotetramat in citrus in China.

Stereoselective Bioaccumulation of Water and Soil-Associated Dufulin Enantiomers in Tubifex.

In this study, the stereoselective bioaccumulation of rac-dufulin, pure S-(+)-dufulin, and pure R-(-)-dufulin in Tubifex (Oligochaeta, Tubificida) were analyzed in spiked-water and spiked-soil systems at low and high dose levels. In the bioaccumulation experiments treated with rac-dufulin, the enantioselective behaviors of the enantiomers show that the concentrations of R-(-)-dufulin are higher than those of S-(+)-dufulin at two dose levels. However, when treated with solely pure S-(+)-dufulin and R-(-)-dufulin, no significant difference of concentrations was detected in Tubifex. Furthermore, the calculated accumulation factors in Tubifex indicated that dufulin (racemic or the pure enantiomers) in the spiked-soil treatments had higher bioaccumulation potential than in the spiked-water treatments. The spiked-soil experiments revealed that the dissipation of dufulin in soil was not enantioselective at the enantiomer levels and Tubifex could reduce the concentrations of dufulin in the underlying solid matrix and accelerate its repair and detoxification process.

[Experimental study on xenogenic acellular dermal matrix incorporated with silver].

OBJECTIVE: To investigate the biological characteristics of xenogenic acellular dermal matrix( Xeno-ADM) incorporated with silver, and to observe its effect in grafting. METHODS: Xeno-ADM was prepared with 0. 25% trypsin and 0. 5% triton X-100 , and then it was immersed in 2 g/L silver nitrate solution to prepare xeno-ADM incorporated with silver. The bacterial inhibitory effect of two kinds of xeno-ADM on burn wound was determined, and the histological characteristic of the wounds was observed with optical microscope, transmission electron microscope and scanning electron microscope. The Ag+ content in the xeno-ADM incorporated with silver was measured with atomic absorption spectrometer. Twenty-seven rabbits with full-thickness skin defects on the back were randomly divided into three groups, i. e. split-thickness skin autograft only( group A, n = 9) , xeno-ADM with overlying split-thickness skin autograft( group B, n = 9) , xeno-ADM incorporated with silver with overlying split-thickness skin autograft ( group C, n = 9). The skin specimens from grafted area in each group were harvested at 2,4 and 6 post-operation weeks( POW) and examined under light microscope and transmission electron microscope. The condition of the graft, the contraction degree of the grafts and the historical changes in grafting area were observed at 2,4,6 POW. The survival rate of the grafts was calculated and the proliferative activity of the lymphocyte in each group was determined at 2 POW. RESULTS: 1. Compared with xeno-ADM, the anti-bacterial effect of xeno-ADM incorporated with silver was much better ( P < 0. 05). No epidermis was seen in both types of xenografts ,and the collagen fibers were even in size and arranged regularly, with no obvious degeneration, and the dermis was also devoid of cells and cellular components. The Ag + content in xeno-ADM incorporated with silver measured (2. 7+/-0. 7) mg/g. 2. The grafts in B and C groups presented similar color to that of normal skin at 6 POW, and it was smooth, with fine texture and no scarring. The collagen fibers was arranged regularly, and conjunction between epidermis and dermis, the structure of basal cell desmosome and semi-desmosome were well reconstructed. The grafts in A group was in dark red color, with obvious contraction, and easily broken. The contraction rate in A group at 2,4 and 6 POW were obviously higher than those in B and C groups( P < 0. 05), while no obvious difference was observed between B and C groups. ( P >0. 05). The overall survival rate of the grafts in C group at 2 POW was 91.7% , which was evidently higher than that in A (77.8%) and B (80. 6% ) groups. The lymphocyte proliferative activity exhibited no difference among A, B and C groups( P >0.05). CONCLUSION: The xeno-ADM incorporated with silver has good anti-bacterial effect. In addition, it preserves the basic tissue structure and integral collagen fiber scaffold, without cells to induce rejection, so that it can be used as an ideal dermal substitute.

[Respiratory support with high frequency jet ventilation in severely burned patients with inhalation injury during early postburn stage].

OBJECTIVE: To observe the effects of respiratory support with high frequency jet ventilation (HFJV) in severely burned patients with inhalation injury during early postburn stage. METHODS: Twenty severely burned patients with TBSA of 79.6 +/- 29.3% and inhalation injury were enrolled in the study. Nineteen cases received tracheostomy after admission and only one received nasal intubation. All the patients underwent HFJV to correct hypoxia. The changes in blood gas analysis, respiratory rate and pulse were recorded before and 11 days after the ventilation. RESULTS: Tracheostomy was performed on 2.7 +/- 2.4 postburn days (PBDs), and HFJV was given during 4.4 +/- 2.9 PBDs. PaO(2) was evidently higher during 1 - 3 days after HFJV than that before the ventilation (P < 0.01) and remained at high level for 1 week after HFJV. There was no change in PaCO(2), respiratory rate and pulse during the ventilation. CONCLUSION: HFJV was beneficial in improving oxygenation and without any obvious side effects during the early management of severely burned patients with inhalation injury. This might be an optimal respiratory support pattern.