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1.
A humic‐fraction‐modified silica gel is prepared and used as the adsorbent for various pesticidal carboxylate esters in hexane. The percentage of adsorption, calculated on the basis of the difference in peak areas for most carboxylate esters in hexane, reaches more than 90% in 1 h. The FTIR (Fourier Transform Infrared) Spectroscopy results show that the interaction force leading to the adsorption observed in hexane is dipole‐dipole oriented and is affected negatively both by the steric hindrance created due to the presence of the group near the carbonyl center of esters and the bulky alkyl group attached to an ether linkage. The hydrogen bonding (i.e. strong dipole‐dipole interaction) and π‐π stacking complexation are either absent or the minor force responsible for the adsorption of carboxylate esters in hexane in most cases. Other factors that cause the variation in the percentage of adsorption include the type of liquid phase (e.g. ethyl ether or acetonitrile vs. hexane) and the additive of acidic or basic origin present in the matrix, which renders the desorption approach for analyte adsorbed.  相似文献   

2.
Reaction of an isocyanide with an iminium ion intermediate, formed by reaction between 6‐formyl‐2,3‐dimethoxybenzoic acid and secondary amines (dibenzyl‐ or benzyl(isopropyl)amine) in the presence of silica nanoparticles (silica NPs, ca. 70 nm) proceeds smoothly at room temperature to afford 2,3‐dihydro‐1H‐isoindolone derivatives in high yields.  相似文献   

3.
Packed cartridges have been widely used in solid‐phase extraction. However, there are still some drawbacks, such as they are blocked easily and the method is time‐consuming. In view of the advantages of monoliths, a monolithic extraction material has been directly synthesized in a glass syringe without any gap between the monolith and syringe inner wall. The monolithic syringe was modified with graphene oxide by loading graphene oxide dispersion onto it. The content of graphene oxide and the surface topography of the monolith have been evaluated by elemental analysis and scanning electron microscopy, respectively, which confirmed the successful modification. This prepared graphene oxide‐modified monolithic syringe was directly used as a traditional solid‐phase extraction cartridge. As expected, it shows good permeability and excellent capability for the extraction of quaternary ammonium alkaloids. The sample loading velocity (1–6 mL/min) does not affect the recovery. Under the optimal conditions, good linearities (= 0.9992–0.9998) were obtained for five quaternary ammonium alkaloids, and the limits of detection and quantification were 0.5‐1 and 1–2 μg/L, respectively. The proposed method was successfully applied for the analysis of quaternary ammonium alkaloids in Chinese patent medicine.  相似文献   

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