Example of Internal Standard Method:

The subsequent data were acquired in the flame photometric determination of sodium through internal standard method. Here 10 ppm of lithium was added to the series of standard solutions of sodium and the sample. A ratio of intensity of emission at the wavelengths of sodium and the lithium are provided in Table.

Table: The ratio of intensity of emission at the wavelength of Na and Li during flame photometric determination by internal standard method

Solution

The plot of an intensity ratio versus the concentration of the standard solutions of sodium is provided in Figure.

Figure: Schematic calibration plot of Intensity ratios versus the Concentration during flame photometric determination of sodium by internal standard method

As the intensity ratio for the solution of unknown concentration is 43, we could determine the unknown concentration along with the help of the graph plotted above. An observed ratio for the given sample corresponds to a focus of 5.7 ppm of sodium.