*3.1. Materials*

Dried PUL were provided by the National Institute of Biological Resources. Choline chloride (≥99.0%), oxalic acid, anhydrous (≥98.0%), and malonic acid (≥99.0%) were supplied by Samchun Chemical Co., Seoul, Korea. Succinic acid (≥99.5%) was purchased from Junsei Chemical Co., Japan, Glutaric acid (≥99.0%) was supplied by Daejung Chemicals and Metals, Gyunggi-do, Korea. Adipic acid (≥99.0%) was procured from Sigma Aldrich, USA. Acetonitrile (ACN, CH3CN, 99.9%, Fisher Chemical, Loughborough, UK) was used as a solvent for the mobile phase of HPLC, and acetic acid (CH3COOH, ACS reagent, Sigma Aldrich, St. Louis, MO, USA) was used as an additive.
