Measurement of Absorption and Scattering With an Integrating Sphere Detector: Application to Microalgae

A spectrometer with an integrating sphere (IS) detector was used to measure the absorbance due to scattering and absorption. Analysis of the measurement process showed that two measurements of the absorbance, one with the cuvette placed in the normal spectrometer position, and the second with the cuvette placed next to the entrance aperture of the IS detector, provide enough information to separate the contributions from scattering and molecular absorption. Measurements were carried out with mixtures of microsphere and chromophore solutions. Two cases were examined: microspheres suspended in an aqueous fluorescein solution, and microspheres suspended in an aqueous holmium oxide solution. In both cases, the proposed measurement model gave results which were in good agreement with the expected response. Measurements on microalgae suspensions yielded a molecular absorption contribution and a scattering contribution. The scattering contribution had significant spectral structure which was inversely related to the molecular absorption contribution. The absorption and scattering contributions may provide independent information on the status of chlorophyll molecules and the structure of chloroplasts in microalgae.