Department of Environment and Energy, Sejong University, Seoul, South Korea.
Water Res. 2011 Apr;45(9):2965-74. doi: 10.1016/j.watres.2011.03.013. Epub 2011 Mar 17.
The spectral responses of a leaf litter derived humic substance (LLHS) and Suwannee River fulvic acid (SRFA) upon ultraviolet (UV) A irradiation were characterized using two-dimensional correlation spectroscopy (2D-COS) based on the absorption and the synchronous fluorescence spectra at different irradiation times. A 12 day irradiation on the humic substances (HS) resulted in higher reduction of the absorbance relative to the dissolved organic carbon concentration, suggesting that aromatic chromophores were preferentially oxidized and/or non UV-absorbing compounds were generated by the photobleaching. Synchronous fluorescence spectra revealed the preferential removal of fulvic-like and humic-like fluorophores and delayed response of protein-like fluorescence upon the irradiation. The spectral features at long wavelengths (>430 nm) appear to be affected by intra-molecular interactions of the individual chromophores associated with shorter wavelengths. Absorption-based 2D-COS demonstrated that there are three types of absorption bands for the two HS, which changed sequentially in the order of 290-400 nm → 200-250 nm → 250-290 nm. In addition, two or three distinctive fluorescence bands in response to the irradiation were identified from 2D-COS. The sequential orders and the associated wavelength bands were possibly explained by the irradiation wavelengths and the differences between direct and indirect photochemical reactions. The interpretation of the 2D-COS results was very consistent with the kinetic rate constants individually calculated at several discrete wavelengths. Our study demonstrated that 2D-COS could be used as a powerful tool in identifying distinctive bands of HS that have dissimilar behavior and the associated sequential orders by visualizing the spectral changes at continuous wavelengths.
采用二维相关光谱（2D-COS）技术，基于不同辐照时间下的吸收光谱和同步荧光光谱，对叶源腐殖质（LLHS）和苏万尼河富里酸（SRFA）在紫外（UV）A 辐照下的光谱响应进行了研究。腐殖质（HS）辐照 12 天后，相对于溶解有机碳浓度，吸光度的降低幅度更大，这表明芳香发色团优先被氧化，或者通过光漂白生成了非紫外吸收化合物。同步荧光光谱表明，富里酸样和腐殖酸样荧光团优先被去除，而蛋白质样荧光的响应延迟。长波长（>430nm）处的光谱特征似乎受到与较短波长相关的单个发色团的分子内相互作用的影响。基于吸收的 2D-COS 表明，两种 HS 有三种类型的吸收带，它们依次在 290-400nm→200-250nm→250-290nm 的顺序中发生变化。此外，还从 2D-COS 中确定了两个或三个对辐照有响应的独特荧光带。这种顺序和相关的波长带可能是由辐照波长和直接和间接光化学反应之间的差异解释的。2D-COS 结果的解释与在几个离散波长下单独计算的动力学速率常数非常一致。我们的研究表明，2D-COS 可以作为一种强大的工具，用于通过可视化连续波长下的光谱变化，识别具有不同行为和相关顺序的 HS 的独特波段。
