1 Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
2 Faculty of Applied Chemistry and Materials Science, Politehnica University of Bucharest, Bucharest, Romania.
Appl Spectrosc. 2017 May;71(5):939-950. doi: 10.1177/0003702816660725. Epub 2016 Sep 20.
This work was sparked by the reported identification of man-made cellulosic fibers (rayon/viscose) in the marine environment as a major fraction of plastic litter by Fourier transform infrared (FT-IR) transmission spectroscopy and library search. To assess the plausibility of such findings, both natural and man-made fibers were examined using FT-IR spectroscopy. Spectra acquired by transmission microscopy, attenuated total reflection (ATR) microscopy, and ATR spectroscopy were compared. Library search was employed and results show significant differences in the identification rate depending on the acquisition method of the spectra. Careful selection of search parameters and the choice of spectra acquisition method were found to be essential for optimization of the library search results. When using transmission spectra of fibers and ATR libraries it was not possible to differentiate between man-made and natural fibers. Successful differentiation of natural and man-made cellulosic fibers has been achieved for FT-IR spectra acquired by ATR microscopy and ATR spectroscopy, and application of ATR libraries. As an alternative, chemometric methods such as unsupervised hierarchical cluster analysis, principal component analysis, and partial least squares-discriminant analysis were employed to facilitate identification based on intrinsic relationships of sample spectra and successful discrimination of the fiber type could be achieved. Differences in the ATR spectra depending on the internal reflection element (Ge versus diamond) were observed as expected; however, these did not impair correct classification by chemometric analysis. Moreover, the effects of different levels of humidity on the IR spectra of natural and man-made fibers were investigated, too. It has been found that drying and re-humidification leads to intensity changes of absorption bands of the carbohydrate backbone, but does not impair the identification of the fiber type by library search or cluster analysis.
这项工作的起因是，据报道，傅里叶变换红外（FT-IR）透射光谱和库检索将人造纤维素纤维（人造丝/粘胶纤维）鉴定为海洋环境中塑料垃圾的主要成分。为了评估这些发现的合理性，使用傅里叶变换红外光谱法对天然纤维和人造纤维进行了检查。比较了透射显微镜、衰减全反射（ATR）显微镜和 ATR 光谱获得的光谱。采用库检索，结果表明，根据光谱采集方法的不同，鉴定率存在显著差异。研究发现，仔细选择检索参数和光谱采集方法对于优化库检索结果至关重要。当使用纤维的透射光谱和 ATR 库时，无法区分人造纤维和天然纤维。ATR 显微镜和 ATR 光谱以及 ATR 库采集的 FT-IR 光谱成功地区分了天然和人造纤维素纤维。作为替代方法，采用无监督层次聚类分析、主成分分析和偏最小二乘判别分析等化学计量学方法，基于样品光谱的固有关系进行鉴定，并成功地对纤维类型进行了区分。根据预期，观察到了ATR 光谱因内部反射元件（锗与金刚石）的不同而产生的差异；然而，这些差异并未影响化学计量分析的正确分类。此外，还研究了不同湿度水平对天然和人造纤维的红外光谱的影响。结果发现，干燥和重新加湿会导致碳水化合物骨架吸收带的强度发生变化，但不会通过库检索或聚类分析损害纤维类型的识别。
