Abstract

The sorption and desorption of a mixture of phenolic acids by the kaolinite modified with aluminum hydroxide was studied in the presence of acetate buffer. The experiments were performed in a 1-mL flow-through microcolumn in 5 and 50 mM sodium acetate buffer (pH 4.5) at a flow rate of 0.5 mL/min. The total concentration of phenolic acids was 0.01 mg/mL (0.06 mM); the concentration of each acid was 0.01 mM. Sodium acetate buffer (5 and 50 mM, pH 4.5) and 50 mM sodium acetate buffer supplemented with 0.1 mM oxalic acid were used for desorption. The concentration of phenolic acids was determined by reverse phase high-pressure liquid chromatography. The following order of sorption was observed: gallic > protocatechuic \( \gg \)p-hydroxybenzoic ~ vanillic ~ ferulic ~ syringic acid. The sorption of phenolic acids in 50 mM buffer comprised 18–35% of their sorption in 5 mM buffer, suggesting the competition of acetate ions and phenolic acids for binding sites on the mineral. The order of desorption of phenolic acids was opposite to the order of sorption and generally correlated with the stability constants of the phenolic acid complexes with aluminum hydroxide. All acids, except for gallic and protocatechuic acids, were weakly bound to the mineral and were almost completely (88–98%) desorbed with 5 mM acetate buffer. The total desorption of gallic and protocatechuic acids by all eluents comprised 25 and 45% of their sorbed amount, respectively. Desorption was significant only in 50 mM acetate buffer (12 and 23%) and in the same buffer with 0.1 mM oxalic acid (10 and 15%). Thus, it has been shown that the distribution of phenolic acids between the solid phase and solution is largely determined by the presence of competing aliphatic compounds. Based on desorption experiments, we propose possible types of complexes of phenolic acids and aluminum hydroxide on the surface of the mineral.

中文翻译：

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乙酸和乙酸根离子对改性高岭石吸附-解吸酚酸混合物的影响

摘要

在乙酸盐缓冲液的存在下，研究了用氢氧化铝改性的高岭石对酚酸混合物的吸附和解吸。实验是在1mL流通式微柱中在5和50 mM乙酸钠缓冲液（pH 4.5）中以0.5 mL / min的流速进行的。酚酸的总浓度为0.01 mg / mL（0.06 mM）；每种酸的浓度为0.01 mM。解吸使用乙酸钠缓冲液（5和50 mM，pH 4.5）和补充有0.1 mM草酸的50 mM乙酸钠缓冲液。通过反相高压液相色谱法测定酚酸的浓度。观察到以下吸附顺序：没食子>原儿茶\（\ gg \）p-羟基苯甲酸〜香草酸〜阿魏酸〜丁香酸 50 mM缓冲液中酚酸的吸附量占5 mM缓冲液中酚酸吸附量的18–35％，这表明乙酸根离子和酚酸竞争矿物上的结合位点。酚酸的解吸顺序与吸附的顺序相反，并且通常与酚酸与氢氧化铝的配合物的稳定性常数相关。除没食子酸和原儿茶酸外，所有酸均与矿物弱结合，并用5 mM乙酸盐缓冲液几乎完全解吸（88–98％）。所有洗脱液对没食子酸和原儿茶酸的总解吸分别占其吸附量的25％和45％。仅在50 mM乙酸盐缓冲液（12％和23％）中以及在具有0.1 mM草酸的相同缓冲液（10％和15％）中，解吸才有意义。因此，已经表明，酚酸在固相和溶液之间的分布在很大程度上取决于竞争性脂族化合物的存在。基于解吸实验，我们提出了矿物表面上酚酸和氢氧化铝配合物的可能类型。