The influence of tetrahydroxyborate ions on the electrophoretic mobility of humic acids was evaluated by capillary electrophoresis (CE). Depending on the molarity of borate ions in the separation buffer, the humic acids exhibit electropherograms with sharp peaks consistently extending from a “humic hump”. The variations in the migration times of these peaks depend on the concentration of borate ions in the separation buffer. The complexation of borate ions and humic acid fractions was also analyzed with 11B and 1H NMR spectroscopy as well as UV spectrophotometry in solutions of the same composition as the CE separation buffers. Supplementary studies with model compounds (flavonoids, phenolic and sugar acids) indicate reaction mechanisms that include the formation of bidentate esters (monocomplexes) as well as spiranes (tetradentate esters or dicomplexes) within the humic substructure. Special attention must be given to the interpretation of CE electropherograms while fingerprinting humic substances with borate buffers since observed peaks do not necessarily indicate distinct humic components but may be artifacts caused by the interaction of the borate ions with the humic substances.
通过毛细管电泳(CE)评估了四羟基
硼酸根离子对
腐殖酸电泳迁移率的影响。根据分离缓冲液中
硼酸根离子的摩尔浓度,
腐殖酸的电泳图谱中会出现从“腐殖质峰”延伸出的尖锐峰。这些峰的迁移时间变化取决于分离缓冲液中
硼酸根离子的浓度。在成分与CE分离缓冲液相同的溶液中,还通过11B和1H NMR光谱以及紫外分光光度法分析了
硼酸根离子与
腐殖酸组分的络合情况。对模型化合物(
黄酮类化合物、
酚酸和糖酸)的补充研究表明,反应机理包括在
腐殖酸亚结构内形成二齿酯(单复合物)和螺环(四齿酯或二复合物)。在用
硼酸缓冲液对腐殖质进行指纹识别时,必须特别注意CE电泳图的解释,因为观察到的峰并不一定表示明显的腐殖质成分,而可能是
硼酸根离子与腐殖质相互作用产生的假象。