Fig. 2.

Negative-ion ESI mass spectra of oligouronic acid fractions F1, F3, F5 and F7, which were collected by preparative HPLC and then subjected to desalination. DP1-5 refers to the degree of oligomer polymerization. The ESI–MS conditions were as follows: injection volume, 2 F7; ESI voltage, 4 kV; capillary temperature, 275 °C; capillary voltage, 350 V; tube lens, 250 V; scan range, 400–2000 m/z. Nitrogen was used as the sheath gas and auxiliary gas at a flow rate of 30 and 5 arb, respectively. The mobile phase (methanol/water = 1:1, v/v) was delivered at a flow rate of 200 μl/min