Taking the separation of PMP-X2 and PMP-X3 as an example, the retention behavior and resolution of PMP-XOS were obviously affected by the pH value of the buffer and the proportion of acetonitrile. The separation degree of PMP-X2 and PMP-X3 (Fig. 1A) was dropped and the retention time (RT) was reduced with the pH value increasing from 5.0 to 7.0, when the acetonitrile proportion remained at 20%. The Fig. 1B showed that the elution of PMPXOS became faster with the proportions of acetonitrile increased while the resolution decreased simultaneously. The concentration of ammonium acetate played little role in the separation of PMPXOS, however, the column pressure increased at the high concentration
of ammonium acetate buffer (Fig. 1C). The flow rate has a neglectable influence on the separation of PMP-XOS, but the column pressure rapidly increased when the flow rate changed from 0.8 mL/min to 1.2 mL/min (Fig. 1D).