A mathematical model for improving the ion chromatography method by applying external adjustment standards

•A mathematical model based on interpolation can improve the results obtained by IC.•Adjusting the results obtained by IC involves the use of external standards.•The adjustment factor is calculated based on the values of the external standard.•The applied method can improve the results by up to a few percent.•IC involves fewer operations on the sample compared to other methods (eg. UV–Vis).