A number of discrepancies in the spectrophotometric determination of plant pigments with the Richards with Thompson method have been reported. A revised set of equations for the determination of plant chlorophylls and a new equation for the approximate estimation of plant carotenoids are presented.
Parsons, T. R., and J. D. Strickland. 1963. "Discussion of spectrophotometric determination of marine-plant pigments, with revised equations for ascertaining chlorophylls and carotenoids." Journal of Marine Research 21, (3). https://elischolar.library.yale.edu/journal_of_marine_research/1003