Extraction study of algal pigments in river bed sediments by applying factorial designs

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Phytopigment content of river bed sediments changes in response to different concentrations of available nutrients and results in a useful descriptor of their trophic state and environmental quality. In this work three incomplete factorial designs of experiments were carried out for extracting algal pigments from river sediments using dimethylsulphoxide (DMSO), methanol or acetone. The independent variables used in this study and their variation limits were: extractant:sediment ratio (1–5 mL/g), temperature (40–80 °C) and duration of treatments (30–90 min). The experimental data obtained (chlorophyll- a, chlorophyll- b and total carotenoids content) allowed the development of empirical models for each phytopigment, describing the interrelationship between operational and experimental variables by equations, including linear, interaction and quadratic terms. The experimental results obtained showed that methanol and acetone were less effective extractants for phytopigments from river sediments when compared to DMSO. The model predicted that in a single extraction using 3.6 mL of DMSO/g of sediment at 38 °C during 40 min, DMSO releases the 89% of chlorophyll- a in the range tested, whereas the best conditions for extracting chlorophyll- b and total carotenoids are achieved using 3.6–3.7 mL of DMSO/g of sediment, at 64–67 °C for 50–51 min, respectively, releasing the 76% of the chlorophyll- b and the 100% of the total carotenoids in a single extraction.