In chemical analysis, matrix refers to the components of a sample other than the analyte[1] of interest. The matrix can have a considerable effect on the way the analysis is conducted and the quality of the results are obtained; such effects are called matrix effects.[2] For example, the ionic strength of the solution can have an effect on the activity coefficients of the analytes.[3][4] The most common approach for accounting for matrix effects is to build a calibration curve using standard samples with known analyte concentration and which try to approximate the matrix of the sample as much as possible.[2] This is especially important for solid samples where there is a strong matrix influence.[5] In cases with complex or unknown matrices, the standard addition method can be used.[3] In this technique, the response of the sample is measured and recorded, for example, using an electrode selective for the analyte. Then, a small volume of standard solution is added and the response is measured again. Ideally, the standard addition should increase the analyte concentration by a factor of 1.5 to 3, and several additions should be averaged. The volume of standard solution should be small enough to disturb the matrix as little as possible.