A technique is suggested which allows an estimate to be made of the errors introduced into spectrophotometric measurements by the use of slits of finite width. The technique depends upon approximate analytic expressions for the slit function, the variation of the instrument sensitivity with wave-length, and the variation of the absorption coefficient with wave-length. A slit function is suggested for use with spectrophotometers with entrance and exit slits of equal width but with optics of varying dispersion. Expressions are derived for two convenient approximations for the absorption coefficient in the neighborhood of a maximum: a parabolic form, and two intersecting straight lines of opposite slope. Application of these expressions is made to experimental data on solutions of benzene, oxyhemoglobin, and neodymium chloride.
W. H. EBERHARDT, "Slit-Width Effects in Spectrophotometry," J. Opt. Soc. Am. 40, 172-176 (1950)