The large-scale simultaneous extraction and concentration of aqueous solutions of triazine analogs, and aflatoxins, through a hydrocarbon-based membrane (e.g., polyethylene, polyethylene/polypropylene copolymer) under ambient temperature and atmospheric pressure is reported. The subsequent adsorption of analyte in the extraction chamber over the lignin-modified silica gel facilitates the process by reducing the operating time. The maximum adsorption capacity values for triazine analogs and aflatoxins are mainly adsorption mechanism-dependent and were calculated to be 0.432 and 0.297 mg/10 mg, respectively. The permeation, and therefore the percentage of analyte extracted, ranges from 1% to almost 100%, and varies among the solvents examined. It is considered to be vapor pressure- and chemical polarity-dependent, and is thus highly affected by the nature and thickness of the membrane, the discrepancy in the solubility values of the analyte between the two liquid phases, and the amount of adsorbent used in the process. A dependence on the size of the analyte was observed in the adsorption capacity measurement, but not in the extraction process. The theoretical interaction simulation and FTIR data show that the planar aflatoxin molecule releases much more energy when facing toward the membrane molecule when approaching it, and the mechanism leading to the adsorption.
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 p-p 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.
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