the basic and neutral substances were separated with a 0.1 m sodium citrate/citric acid buffer system ( ph 4.0 ) containing 1 % tetrahydrofuran , and the acidic ones with 0.075 m sodium citrate/citric acid buffer ( ph 3.5 ) containing 1 % tetrahydrofuran , 10 % methanol , and 12 % acetic acid .
C0055819
citric acid
C0304465
sodium citrate/citric acid