Relative influence of the dissolved humic material on the solid-phase extraction efficiency of pesticides from environmental water

The effect of organic matter on the solid-phase extraction (SPE) efficiency for pesticides belonging to different chemical groups (urea-derivatives, carbamates and triazines) and having different polarities, was simultaneously studied for the first time in pure and simulated water samples. SPE was carried out in precolumns packed with C18 silica or styrene-divinylbenzene copolymer PLRP-S phases on-line coupled to high performance liquid chromatography (HPLC) analysis. Retention factors in water (k'(W)) were estimated for 25 compounds and used for the calculation of the theoretical breakthrough volume (Vb(T)) in pure water. Experimental breakthrough volumes (Vb(E)) were first determined using purified and deionized water as the matrix for selected compounds having Vb(T) < 500 mL; then, the same water with an added humic acid sodium salt (HA) at 0.4-5.6 mg/L of dissolved organic carbon (DOC) content, was used as the matrix for compounds having VbE < 500 mL in pure water. Several polar pesticides showed negative linear or logarithmic Vb(E) curves depending on HA content; their recoveries were also determined in environmental samples having low dissolved organic carbon values, between 0.5-6.4 mg/L. A similar behavior was observed for these compounds in simulated and natural water samples, where DOC concentration and the percolated volume (Vp) mainly determine the solute recoveries values. However, the variation of recoveries as a function of DOC content could be negative or null depending on the two examined conditions (Vp lower or larger than Vb(E) in pure water). Results demonstrated that breakthrough volume must always be considered to correctly interpret the participation of dissolved humic material on the SPE efficiency of organic micropollutants in water.     

有机改性剂对水中有机氯农药提取效率的影响研究

通过有机改性剂在液液萃取和固相萃取条件下水中有机氯农药的提取效率比对分析,首次探讨了有机改性剂对水中有机氯农药提取效率的影响。结果表明,（1）液液萃取前处理水样中不加有机改性剂、固相萃取前处理水样中添加一定量有机改性剂时,水中有机氯农药的提取效率较高;（2）采用正交实验优化水中有机氯农药固相萃取的提取效率实验表明,有机改性剂添加量对其影响大于有机改性剂种类对其影响;最佳优化方案为水样中添加1%甲醇时,提取效率最高。     

活性炭多维电极法去除水中腐殖酸过程与宏观动力学研究

采用活性炭多维电极法去除水中溶解态腐殖酸。实验结果表明 ,与活性炭单纯吸附法相比 ,活性炭多维电极法可显著提高对溶解态腐殖酸的去除率 ;在连续运行条件下 ,延长水力停留时间、升高槽电压、溶液偏碱性有利于腐殖酸的去除 ;高效液相色谱分析结果表明 ,电极的氧化还原作用可使有机物分子量变小或矿化 ,因而处理系统有可能延长活性炭的使用寿命     

Influence of suspended clay minerals and humic matter on the solid phase extraction efficiency of selected pesticides from water

The purpose of this investigation was to determine the influence of humic acids (HA) and Ca-montmorillonite (CaM) on the solid-phase extraction (SPE) efficiency of atrazine, alachlor and alpha-cypermethrin from water samples at various pH-values. The nature and intensity of binding of the studied pesticides to CaM were determined by X-ray diffraction analysis and termogravimetric analysis (TGA) test. The studied pesticides eluted from discs were analysed by thin-layer chromatography (TLC). The effects of CaM and humic acid were generally pH-dependent and acted independently in extraction efficiency influence. Lower recovery of pesticides was observed at higher pH values when CaM was > or =0.1 g and was attributed to greater dispersion of clay, increased surface area and subsequent adsorption. Concentrations of dissolved organic carbon (DOC) in humic acid had less effect on the extraction efficiency when water was at pH 8 compared to water at pH 2, which was probably due to greater nonpolar interactions of the pesticides to the charge-neutralized humic acid molecule.