Direct through-container Raman spectroscopic analyses of samples housed in glass and plastic containers: a review

This review summarizes current trends in direct through-container Raman spectroscopic analyses of housed samples without external sampling. Nonsampling Raman measurement is a relatively simple technique that avoids damaging or contaminating a sample's commercial value by opening the container. The most demanding aspect of such techniques is the need to minimize or eliminate spectral interference from the container when analyzing the housed samples. To reduce the spectral peaks associated with the container, which can be either fluorescent or nonfluorescent, various measurement configurations, including spatially offset Raman scattering and/or algorithm-based background subtractions, have been employed. Here, reports on the former technique are categorized according to their analytical purposes into qualitative chemical identification and quantitative determination of component concentrations of housed samples. Studies in each group are further classified by container material, either glass or polymer (plastic), as the optical properties of each, as well as the dominance of their Raman spectral peaks, are different. Prospects for advances and unresolved issues in through-container Raman measurement are also discussed.