THE DECONVULATION OF ABSORPTION SPECTRA OF GREEN PLANT MATERIALS—IMPROVED CORRECTIONS FOR THE SIEVE EFFECT

The extinction (absorbance, optical density) of a suspension of algal cells or chloroplasts, etc. can be an a linear function of the absorption coefficient of the cell contents, even when the effects of scattering are negligible. The deviation from linearity is Duysens' sieve effect. The heights of absorption maxima of suspensions are depressed as compared with those of the “particle” contents. Duysens proposed an expression for correcting for this distortion; that expression proves to be a special approximate case of a more general one. This paper proposes an improved method of correction which utilizes this general expression, conventional expressions for particle absorption based on the Lorentz-Mie and Aden and Kerker equations for scattering and absorbing, and iterative methods for numerically deducing particle absorption coefficients from suspension parameters. The procedure is illustrated by applying it to previous experimental spectra of Chlorellu cells and spinach chloroplasts.