The mobile phase consisted of 0.6% methanol, 0.341 mM 1-octanesulfoic acid sodium salt, 168.2 mM sodium acetate, 66.6 mM citric acid monohydrate, 0.025 mM disodium ethylenediamine tetraacetate (EDTA) and 0.71 mM triethylamine adjusted to pH 4.0–4.1 with acetic acid.