LKAB is located in northern Sweden and is a world-leading producer of refined iron ore products that are delivered to customers around the world. LKAB's mining contributes, among other things, to the weathering of sulphide minerals and calcium sulphates, which increase the concentration of sulphate in the recipient. The Swedish government has not established the threshold value for sulfate in the environment, but sulfate is an increasing problem for the mining industry. It is therefore interesting to analyze the lev-els of sulphate. In recent years, LKAB has carried out pilot projects to study different purification techniques to minimize the emissions of sulfate to the nearby water envi-ronment. Ion analysis is important in analytical chemistry and environmental chemistry and can be performed both with classic wet chemical methods and with new efficient and repeatable analysis methods such as Ion Chromatography (IC). IC plays a dominant role in ion determinations and has been accepted worldwide for the analysis of, among other things, anions as a reference method. LKAB carries out environmental analysis of, among other things, the anion sulfate with IC. The aim of the thesis was to create an optimal curve fit for sulphate analyzed with IC. By finding out the sulfate content from LKAB's nearby water environment, which was ana-lyzed with IC, the measurement range of the test method was determined. The raw data of the test method was subjected to a regression analysis to study which polynomial re-generated the analysis results with satisfactory certainty. The following parts are in-cluded in regression analysis, linear polynomial, quadratic polynomial, cubic polyno-mial, LOQ, LOD, Wald–Wolfowitz test, residuals, weighted residuals, the correlation co-efficient, the coefficient of determination, the adjusted coefficient of determination, and the relative error that occurs when analyzing control samples. The test method's measurement range included 19 measurement points between 1.2-104mg/l. The coefficient of determination corrected for the number of degrees of free-dom was calculated closer to 1 and the relative error was smaller for the linear polyno-mial in comparison to other polynomials included in the regression analysis. Visually, the spread of positive and negative residuals was evenly distributed around the mean and shows a linear relationship. Also, the Wald – Wolfowitz test showed that the spread of the residuals has a random distribution. The calculated LOQ value was lower in com-parison with the lowest sulfate concentration that was included in the measurement range of the test method. A validation of the test method must be carried out before the test method can be used as a routine by LKAB.