The absorption spectra of photosynthetic algae are characterized by a conti
nuous envelope, which is a result of the overlapping spectra of the indivua
l pigments. This feature makes it difficult to estimate the contribution of
each pigment to the total absorption spectra. Derivative analysis is an ob
jective tool for isolating absorption peaks in phytoplankton. Theoretically
, electrons and ions of interacting molecules can be regarded as simple har
monic oscillators in an electromagnetic field, which result in a Lorentzian
shape. However, when measured by an optical spectrophotometer the signal i
s transformed into a Gaussian curve. Thus, a combination of both types of c
urve provides a realistic approach to the decomposition of absorption spect
ra. In this study derivative analysis is performed on absorption spectra in
order to prove that the method can be successfully used to identify the in
dividual absorption spectra of component pigments. The spectra used are mod
elled phytoplankton, spectrophotometric measurements of algal cultures and
samples from natural waters. A combination of Gaussian-Lorentzian shaped cu
rves, centred on the identified peaks, were compared with the original spec
tra and showed good agreement.