Internal standards can significantly improve the accuracy of the analytical data, as an internal standard provides a reference that can be used to correct for variability between the calibration standards and the samples. The most common example is correcting for matrix differences between the calibration standards and samples, and the key criteria for using an internal standard are: 1) it must not be present in the sample, 2) it must be free from interferences, 3) it’s added in equal concentrations to all analytical solutions (blanks, calibration standards, and samples).