Standard solutions are commonly used to determine the concentration of an analyte species via calibration curve. A calibration curve is obtained by measuring a series of standard solutions with known concentrations, which can be used to determine the concentration of an unknown sample using linear regression analysis. For example, by comparing the absorbance values of a solution with an unknown concentration to a series of standard solutions with varying concentrations, the concentration of the unknown can be determined using Beer's Law.
Any form of spectroscopy can be used in this way so long as the analyte species has substantial absorbance in the spectra. The standard solution is a reference guide to discover the molarity of unknown species.
The matrix effect can negatively affect the efficiency of a calibration curve due to interactions between matrix and the analyte response. The matrix effect can be reduced by the addition of internal standards to the standard solutions, or by using the standard addition method.