Applications Of Combined Extinction/Absorption Spectroscopy – Dairy Analysis, Microplastics Study, And Vitamin Assessment

Combined extinction/absorption spectroscopy is the combination of conventional ultraviolet and visible spectroscopy (UV Vis Spectroscopy) and diffuse-light absorption spectroscopy, i.e. using an integrating sphere (IS), in one instrument. The combination provides two optical properties of the sample in one trial, i.e. extinction and absorption. Scattering is computed by subtracting absorption from extinction. Hence, we obtain three UV Vis spectra of the sample in one measurement – extinction, absorption, and scattering. This information is important to understand the optical behavior of the sample or its interaction with UV Vis radiation. In addition, the integrating sphere could provide information of turbid media through its absolute absorption spectra when scattering is a matter. It is promising in real-time analyzing practical samples such as waste water, bio-fluid, or food.

This research aims to apply combined extinction/absorption spectroscopy into investigating the optical properties of materials – absorption and scattering, as well as chemical information of turbid samples through the absolute absorbance that could not be studied by a standard UV Vis spectrometer. It is promising for practical samples in environment, food, and biomedicine because most of them are too cloudy to be measured directly by a conventional setup. Three projects are run – microplastics study, dairy analysis, and vitamin assessment.

In dairy analysis, it showed peaks of nutrients – fat, protein, vitamin A, vitamin B2, and beta-carotene in a number of milk types and cream. In addition, the Lambert-Beer lines are constructed for fat and protein content in milk and cream. Preliminarily, they are linear in low concentration and non-linear in higher ones. Some hypotheses are raised to explain these phenomena.

In microplastics study, commercial latex sphere polystyrene samples with different diameters are measured and their optical properties or UV Vis spectra are harvested – extinction, absorption, and scattering. One investigation that has not been reported yet is their absorption in UV range shown by comparing with their electromagnetic models.

In vitamin assessment, dissolution study of complex vitamin B and vitamin C effervescent tablet showed real-time release of active agents by the absorption spectra.