A Note of Caution on Using Absolute Methanol Concentrations and Low Temperatures to Quantify Mycosporine-Like Amino Acids in Algae

Mycosporine‐like amino acids (MAAs), a family of UV‐absorbing compounds, are widespread among many marine and freshwater organisms, however, no standard method to analyze these compounds is available. Consequently, protocols to extract MAAs largely differ, for example, in the type of solvent, concentrations, temperatures, and times used. In this study, we tested whether the concentrations of MAAs are affected by extraction at different temperatures and methanol (MeOH) concentrations. Natural assemblages of freshwater phytoplankton and the marine alga Porphyra sp. were used as test organisms. The MAAs shinorine, palythine, MAA 331, asterina‐330, and porphyra‐334 present in the organisms examined were generally best extracted at 45 °C in 25% aqueous MeOH. In Porphyra sp. and natural freshwater phytoplankton, the mean total MAA concentrations obtained with this protocol were, respectively, about 13 and 3 times higher than when extracted in 100% MeOH at 4 °C. Depending on the organism examined, both MeOH concentration and temperature affected extraction efficiency and final MAA concentration. Our results stress the need for a priori testing the influence of these variables to assure that the highest concentration is obtained without altering the qualitative MAA composition. Based on these results, direct comparison of MAA concentrations reported in the scientific literature should be done with caution.