8 - Multivariate analysis of extracted pigments using spectrophotometric and spectrofluorometric methods

Summary

Introduction

The spectral absorption and fluorescence properties of chlorophylls and pheopigments have been exploited in the past to determine the concentration of a few extracted pigments using simultaneous equations (the so-called di- or trichromatic methods). Spectrophotometric, fluorometric and spectrofluorometric techniques for pigment extracts from oceanographic samples were reviewed and compared in the 1997 volume edited by Jeffrey et al., Phytoplankton Pigments in Oceanography (Chapters 4, 14 and Appendix F in Jeffrey et al., 1997).

Recently, advanced chemometric methods developed for multi-component analysis have been applied to the analysis of pigment extracts (Neveux and Lantoine, 1993; Moberg et al., 2001; Naqvi et al., 2004). The use of full spectrum techniques enhances the information acquired from phytoplankton samples, and chemometric methods have been shown to be a valuable tool to extract accurate pigment concentrations from this information (Moberg et al., 2001). The major advantage of these methods is that a greater number of pigments can be determined even if they have overlapping spectra, because a greater part of the information contained in the absorption or fluorescence spectra is being employed than was the case with the di- or trichromatic equations implemented in earlier work. Recent studies pointed out that simultaneous equations such as those used in trichromatic methods may yield inaccurate results because of interference from compounds other than the two or three pigments assessed with these methods (Naqvi et al., 1997, 2004; Küpper et al., 2007). This was acknowledged in the 1997 volume (Jeffrey and Welschmeyer, 1997; Humphrey and Jeffrey, 1997).