Raman microspectroscopic analysis of fibers in beverages†
This technical note illustrates the applicability of Raman microspectroscopy (RM) for the analysis of the synthetic fiber content in different beverages (beer and mineral water). The particles and fibers were collected by filtration on a cellulose nitrate membrane filter (pore size = 0.45 μm) and subsequently identified and quantified by RM. Our results show no significant differences (p = 0.95) in the statistical distribution of fibers in beverage and blank samples, which suggests external contamination sources. Moreover, most of the identified fibers consisted of cellulose, which is a natural fiber and harmless compared to synthetic fibers. The other fibers identified were mainly made of polyethylene, which is used as a packaging material for the cellulose nitrate filter. Our study highlights the need for spectroscopic analysis as well as the use of adequate blank samples and an almost particle-free lab environment. Spectroscopic identification is crucial for the discrimination between cellulose and synthetic fibers; otherwise artefacts cannot be recognized and the interpretation will be misleading. The qualitative and quantitative analysis performed in our laboratory could not confirm the contamination of beverages with synthetic fibers reported by previous studies which relied on optical identification alone.