A solvent system consisting of 0.1% acetic acid in water (solvent A) and acetonitrile
(solvent B) was used with the following gradient: starting with 100% A and installing a gradient to obtain 8% B at 12 min, 10% B at 24 min, 30% B at 44 min, 90% B at 54 min, 100% B from 55 to 58 min and finally 5% B at 59 min