Selection of protocols for phytoplankton pigment analysis: a comparative study

Pigments are widely used as indices for estimation of phytoplankton biomass and composition, and many protocols have been developed to analyze pigments in phytoplankton. Different protocols were compared using four solvents (methanol, 95% methanol, dimethylformamide, and 90% acetone) and two instruments (fluorometer and high-performance liquid chromatography (HPLC) coupled with diode array detector). Analysis of chlorophyll a (Chl a) with fluorometer could lead to over- or underestimation due to the interference from its derivatives in all probability. Among the four extractants, 90% acetone had a high recovery for chlorophylls. In contrast, 95% methanol was a poor extractant for chlorophylls due to the degradation of Chl a, especially in diatoms. The 95% methanol, however, had high extraction efficiencies for most diagnostic xanthophylls. Therefore, the selection of pigment analytical protocols should follow the specific purpose of phytoplankton study. In addition to fluorometry, an HPLC method with 90% acetone as extractant shall be a good choice for the analysis of Chl a to estimate phytoplankton biomass, especially for diatom-dominated samples, while an HPLC method with 95% methanol as extractant be more suitable to characterize different taxa in phytoplankton communities.