pH值和离子对诺氟沙星在胡敏酸上吸附特征的影响

根据OECD Guideline 106批平衡实验,研究了pH值、Ca2+浓度和离子类型对诺氟沙星在胡敏酸上吸附特征的影响.结果表明,吸附系数(Kd)随着pH值的增大有先增加后减小的趋势,在pH 4.0和pH 6.0时吸附系数较大.红外光谱表明,pH 3.0有利于诺氟沙星和胡敏酸形成氢键; pH6.0和7.0时胡敏酸的羧基可能与诺氟沙星的氨基形成了肽键.诺氟沙星在胡敏酸上的吸附量和Kd值随着溶液中Ca2+离子浓度的增加而逐渐减小,表明两者之间存在阳离子吸附和竞争吸附.不同类型的阳离子和阴离子的加入都能导致诺氟沙星在胡敏酸的吸附特性存在差异.阳离子的影响趋势主要为价态的影响,即价态越高,在胡敏酸表面吸附位点的吸附能力就越强,对诺氟沙星吸附阻碍作用越显著,表现在诺氟沙星的最大吸附量(Qm)为:M+ (Na+、K+、NH4+) >M2+ (Mg2+、Ca2+、Zn2+);其次受阳离子的离子半径和水解作用的影响.而只有能水解的阴离子才能对诺氟沙星在胡敏酸上的吸附产生明显的阻碍作用.

Influence of pH and ions on sorption of norfloxacin on humic acid

The influences of pH, concentrations of Ca2+, and ion types on sorption characteristics of norfloxacin (Nor) on humic acid (HA) were investigated by batch equilibrium studies according to OECD Guideline 106. Sorption coefficient (Kd) tended to increase with pH increasing in the range of 3.0~4.0, but to decrease as pH increase in the range of 6.0~7.0. The Kd values had two peaks at pH 4.0 and 6.0 than those at other tested pH values. The FTIR spectra of HA before and after hydrogen bonds were favorably formed at pH 3.0 between HA and Nor, while peptide bonds were likely formed between carboxyl group of HA and amino group of Nor at pH 6.0 and 7.0. The Kd values and sorption amounts of Nor gradually decreased with the increasing concentration of Ca2+, indicating that the cation exchange and completion sorption occurred between Nor and Ca2+. Addition of different cations and anions in solution led to different sorption characteristics of Nor. The valencies of different cations played the dominating role in affecting the sorption of Nor on HA. The higher valencies cations, the more strongly cations were adsorbed on surface sorption sites of HA, resulting in the following order of the maximum sorption amounts (Qm) for Nor: M+ (Na+、K+、NH4+) > M2+ (Mg2+、Ca2+、Zn2+). On the other hand, the radius and the hydrolysis of cations could also influence the sorption of Nor. The inhibition effect of anions on Nor sorption became pronounced when the hydrolytic anions were added in solution.