In the internal standard method, a

In the internal standard method, a known amount of a reference species is added to all the samples, standards, and blanks. The response signal is then not the analyte signal itself but the ratio of the analyte signal to the reference species signal. A calibration curve is prepared where the y-axis is the ratio of responses and the x-axis is the analyte concentration in the standards as usual. Figure 8-12 illustrates the use of the internal standard method for peak-shaped responses.The internal standard method can compensate for certain types of errors if these influence both the analyte and the reference species to the same proportional extent. For example, if temperature influences both the analyte and reference species to the same extent, taking the ratio can compensate for variations in temperature. For compensation to occur, the reference species is chosen to have very similar chemical and physical properties to the analyte. The use of an internal standard in flame spectrometry is illustrated in Example 8-7.