Gu Cheng, Karthikeyan K G, Sibley Samuel D, Pedersen Joel A
Environmental Chemistry and Technology Program, University of Wisconsin-Madison, Madison, WI 53706, United States.
Chemosphere. 2007 Jan;66(8):1494-501. doi: 10.1016/j.chemosphere.2006.08.028. Epub 2006 Nov 3.
The effect of solution chemistry and sorbate-to-sorbent ratio on the interaction of the antibiotic tetracycline with Elliott soil humic acid (ESHA) was investigated using equilibrium dialysis and FITEQL modeling. Tetracycline speciation strongly influenced its sorption to ESHA. Sorption was strongly pH-dependent with a maximum around pH 4.3, and competition with H+ and electrolyte cation (Na+) was evident. The pH-dependent trend was consistent with complexation between the cationic/zwitterionic tetracycline species and deprotonated sites in ESHA (mainly carboxylic functional groups). Modification of ESHA by Ca2+ addition increased tetracycline sorption suggesting that ternary complex formation (ESHA-metal-tetracycline) may be important at higher concentrations of multivalent metal cations. The macroscopic data (pH-envelope and sorption isotherms) were successfully modeled using a discrete logK function with the FITEQL 4.0 chemical equilibrium program indicating that ESHA-tetracycline interaction could be reasonably represented as complex formation of a monoacid with discrete sites in humic acid. Sorption-desorption hysteresis was observed; both sorption and desorption isotherms were well described by the Freundlich equation.
采用平衡透析法和FITEQL建模研究了溶液化学性质和吸附质与吸附剂比例对抗生素四环素与埃利奥特土壤腐殖酸（ESHA）相互作用的影响。四环素的形态对其在ESHA上的吸附有强烈影响。吸附强烈依赖于pH值，在pH 4.3左右达到最大值，并且与H⁺和电解质阳离子（Na⁺）的竞争明显。pH依赖性趋势与阳离子/两性离子四环素物种与ESHA中去质子化位点（主要是羧基官能团）之间的络合一致。通过添加Ca²⁺对ESHA进行改性增加了四环素的吸附，表明在较高浓度的多价金属阳离子下三元络合物的形成（ESHA-金属-四环素）可能很重要。使用离散logK函数和FITEQL 4.0化学平衡程序成功模拟了宏观数据（pH范围和吸附等温线），表明ESHA-四环素相互作用可以合理地表示为单酸与腐殖酸中离散位点的络合物形成。观察到吸附-解吸滞后现象；吸附和解吸等温线均能很好地用弗伦德利希方程描述。
