高效液相色谱法测定二甲四氯在铁铝土中的吸附特征

Characteristics of MCPA sorption in ferralsol using high performance liquid chromatography

二甲四氯(MCPA)是铁铝土区域广泛使用的一种除草剂,生物毒性大。吸附是控制MCPA在土壤中迁移/转化的关键过程。本研究建立了以C18为色谱柱、V(甲醇):V[水(乙酸调pH值至2.5)]=80:20为流动相、PDA为检测器(检测波长280 nm)的MCPA高效液相色谱检测方法,并结合批量平衡法评估MCPA在铁铝土中的吸附特征。结果表明:在0.5~40 mg/L内,MCPA的质量浓度与对应的峰面积间呈良好线性关系(R^2=0.9999),检出限为0.2 mg/L,定量限为0.5 mg/L;回收率为98%~103%,相对标准偏差为3.5%~4.0%,适用于MCPA吸附试验的测定。铁铝土对MCPA的等温吸附过程符合Freundlich模型,吸附自由能△G<0,|△G|为9.34~14.73 kJ/mol,是一个自发的、非均质的、多层的物理吸附过程。吸附常数Kf值在0.85~4.24 L/kg之间,属于难吸附污染物,对地下水具有环境风险。不同铁铝土对MCPA的吸附作用受土壤pH值、有机质、矿物影响,表现为水稻土>暗红湿润铁铝土>简育湿润铁铝土。氢键结合、偶极间作用是吸附发生的关键作用力。

4-Chloro-2-methylphenoxyacetic acid(MCPA)is a widely used herbicide with high biological toxicity in ferralsol.Sorption is a key process that regulates the behavior of MCPA migration and conversion in soil.In order to evaluate the sorption behavior of MCPA in ferralsol,a simple and sensitive high performance liquid chromatographic method(HPLC)for the determination of MCPA in solution was developed with C18 column and PDA detector set at 280 nm.The mobile phase consisted of a mixture of 80:20(V/V)methanol and distilled water(adjusted to pH value 2.5 with acetic acid).The sorption isotherm experiment was also conducted.The results showed that good linear relationships(R^2=0.9999)between HPLC peak area and the concentration of MCPA was obtained in the range from 0.5 to 40 mg/L.Detection limits(LOD)and quantitation Limit(LOQ)were 0.2 mg/L and 0.5 mg/L,respectively.Satisfactory relative recoveries ranging from 98%to 103%were achieved with relative standard deviations of 3.5%-4.0%.Those results demonstrated that the HPLC method was suitable for the evaluation of MCPA sorption.The isotherm data of MCPA sorption in ferralsols were fitted well by Freundlich model with△G<0 and|△G|=9.34-14.73 kJ/mol,which suggested that MCPA sorption on the ferralsols was an spontaneous,exothermic and anisotropic process dominated by physical forces.The value of Kf for MCPA ranged from 0.85 to 4.24 L/kg,which revealed that MCPA was difficult to be adsorbed by soils.It may further cause a potential environmental risk to groundwater.Moreover,diverse sorption capacity of MCPA was observed among three types of ferralsols in the following order:paddy soil>rhodic ferralsol>haplic ferralsol,which was closely related to the soil pH,organic matter and mineral.The sorption process was dominated by hydrogen bonding and dipole interaction.