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It is possible to determine by use of the some statistical formulas how the internal standard technique affects the reproducibility of a given chromatographic method. The internal standard technique is widely used in chromatography. An accurate amount of a known compound is added to the sample solution prior to analysis. The internal standard technique considerably improves the reproducibility of determinations. Errors are often reduced in the analytical measurement since any loss of sample is compensated by the loss of an equivalent amount of internal standard. Instead of the absolute value of the peak area (or peak height), the ratio of the peak area of the compound to the peak area of the internal standard is used in calibration and in the evaluation of the unknown samples.