运用3DEEMs及荧光偏振方法研究pH、离子强度及浓度效应对腐殖酸荧光光谱特性的影响

利用三维荧光激发.发射光谱(3DEEMs)及荧光偏振法研究了3例腐殖酸和1例湖泊溶解有机物(DOM)在不同腐殖酸浓度、离子强度和pH条件下的荧光光谱特性.实验结果表明,随着浓度增大,各腐殖酸样的荧光强度增大,其中垃圾渗滤液腐殖酸和Pahokee泥炭腐殖酸的荧光峰出现红移.随着浓度进一步增大,腐殖酸的荧光偏振值增大,由此推断在此浓度范围内腐殖酸由于分子间的排斥作用使其构型出现伸展.离子强度增大导致腐殖酸及阿哈湖DOM的荧光强度降低.随着氯化钾(KCI)浓度增大,Fluka腐殖酸的荧光峰A蓝移,荧光峰B的荧光偏振值出现减小,推测是由于静电中和作用使其荧光基团发生卷曲造成的.离子强度对其余腐殖酸样和阿哈湖DOM的其他荧光特性没有明显的影响.总的来说,pH值的变化对腐殖酸和湖泊DOM的荧光特征的影响是很明显的.随着pH值增大,腐殖酸和湖泊DOM的荧光强度增强.而pH值减小时,Fluka腐殖酸和Pahokee泥炭腐殖酸的荧光峰(A峰)蓝移,当pH值降到5时,Fhka腐殖酸的荧光峰突然红移到最大,随后又继续蓝移;垃圾渗滤液腐殖酸和阿哈湖DOM的荧光峰位无明显的漂移.所有样品的荧光偏振值都减小(但阿哈湖DOM的A峰变化不大),但在pHi≤5时又增大,这种现象表明随着pH值降低,腐殖酸和湖泊DOM中有机大分子发生卷曲,但在pH≤5时由于羧基的质子化又以平面伸展构型出现在溶液中.

Application of three-dimensional excitation-emission matrix fluorescence spectroscopy and fluorescence polarization to studying characterization of natural organic substances

Characterization of three humic acids (HA) and a lake dissolved organic matter (DOM) at different concentrations,ionic strengths and pHs was investigated by three-dimensional excitation-emission matrix fluorescence spectroscopy and fluorescence polarization. A red shift in the longer wavelength peak region occurred in the humic acid extracted from the landfill leachate and the Pahokee peat humic acid with increasing concentration of humic acids. Their fluorescence polarization (FP) increased at the same time. This indicated some degree of association occurred in the molecules of the humic acids. The fluorescence intensity of all samples decreased with increasing ionic strength. A blue shift in the shorter wavelength peak region of peak A of the Fluka HA occurred with increasing KCl concentration. The FP of the peak B decreased,which probably resulted from curliness of the fluorophores because of electrostatic neutralization. There was no distinct effect of ionic strength observed on the fluorescence characterization of other humic acids and DOM from Lake Aha. In general,the fluorescence intensity of all samples increased with increasing pH. A blue shift of emission peak of Fluka HA and Pahokee peat HA occurred with decreasing pH,while no distinct peak shift was discovered in the landfill leachate HA and DOM from Lake Aha. Except for peak A of DOM from Lake Aha,the FP of all samples decreased as the pH reduced. However,the FP increased as the pH dropped to 5. This indicates the conformation of the macromolecules in the organic matters was curling as the pH reduced,but it existed in extended flat conformation again as the pH was below to the value of 5 because of the protonation of carboxyl.