To release the sulfate groups, the polysaccharide was subjected to acid hydrolysis. For this purpose, 25 mg of the carrageenan sample were mixed with 2.25 mL of 2.3 M trifluoroacetic acid and 0.25 mL of 35 % (v/v) hydrogen peroxide. Hydrolysis was carried out for 16 h at 100 °C. Subsequently, the samples were cooled to room temperature (20 °C) and then centrifuged for 10 min at 220 x g. After centrifugation, 250 µL of the supernatant was dried by evaporation. The dried residue was dissolved in 3.25 mL of water and treated in a water bath at 70 °C for 15 min . Sulfate analysis was carried out on a Dionex ICS-6000 system (Thermo Fisher Scientific, USA) equipped with a conductivity detector and a Dionex AERS 500e suppressor (4 mm, Thermo Fisher Scientific, USA) to suppress the conductivity of the eluent. 30 mM sodium hydroxide solution was used as the eluent with an isocratic flow rate of 0.38 mL/min. Separation of inorganic ions was carried out on a Dionex IonPac AS10 column (250 x 4 mm, particle size 8.5 µm, Thermo Fisher Scientific, USA) and the column temperature was set at 30 °C.