To analyze the dimer acid, several methods including high-performance liquid chromatography (HPLC) [13–16], gas chromatography [17], and capillary electrophoresis [18] have been employed for the quantitative determination of dimer acids. However, in the case of complex mixtures, these methods require a complicated and time-consuming pre-treatment to extract and concentrate each target compound from the mixture to prepare high purity analytical grade target materials [15,16].