Normalization by Multiplication or Division

It is possible to amplify the highest peaks in both analog spectra or to multiply the digital data by a factor that allows at least two signals to be congruent. Then the possible deviations can be observed on the monitor or after plotting them out. 

Another method is to take the ratios of the peak heights of both spectra and to compare the results (Sec. 2.6.1.4). The ratios must be equal in the case of identical substances even if the concentrations are different (PPR method). This mathematical operation can be carried out by a short computer program. The printout is a set of data given in Table 4-7 for the comparison of trypsin and acetyltrypsin. Note that even small differences in the substances can easily be detected. In the fundamental spectra, the shape of the curves are very similar (Fig. 4-32 a) but the differences become clearly visible if the heights of the corresponding peaks in Fig. 4-32 b are mathematically manipulated. Other examples, such as the comparison of different varieties of beer [2], whale and horse myoglobin [25], and human and bovine hemoglobin [5] can be found in the cited literature. 

---