Phenomenex Kinetex 5 mm C18 100 A˚ column with core–shell particles were
fitted with respective C30 or C18 guard columns, and operated at
35 8C. The mobile phase consisted of (A) methanol/water/1 M
ammonium acetateaq (90:8:2; v/v/v) and (B) methanol/methyl
tert-butyl ether/1 M ammonium acetateaq (20:78:2; v/v/v).