2.3. Gel permeation chromatography (GPC)

Gel permeation chromatography was performed in a Shimadzu HPLC system equipped with degassing unit (DGU-20A3R), high pressure pump (LC-20AD), autosampler (SIL-20A HT), column Oven (CTO-20A), and refractive index detector (RID-10A). Isocratic elution was done using 0.1 M NaCl eluent (flow rate: 0.5 mL min⁻¹; column temperature: 40 °C). The mobile phase and sample solutions were filtered using nylon filter with pore size of 0.45 um. Ultrasonicated κ-carrageenan solutions were analyzed by joining two analytical columns, the SHODEX OHpak SB-805 HQ and SHODEX OHpak SB-804 HQ. The guard column SHODEX OHpak SB-G 6B was also used. The calibration curve was constructed by injecting polyethylene glycol (PEG) and polyethylene oxide (PEO) standards. Samples with concentration of 1.0 mg mL⁻¹ dissolved in 0.1 M NaCl and volume of 100 μL was injected in the columns through the autosampler.