The mobile phase consisted of 0.6% methanol, 0.341 mM 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.