3.3.3. Methyl Peak Profile between 2D Spectra

The peak heights of the 48 identified methyl peaks in 2D 1H-13C spectra of Lantus® and Basaglar® were recorded as *Ix* for peak *x*. The relative peak intensity of the peak *x* (*Rel.Int.x*) was calculated per Equation (3), where *IThr-d* is the peak height of the peak Thr-d, which is the peak with the highest intensity. The mean and standard deviation of *Rel.Int.x* were calculated from the spectra of 5 different lots within each brand (Table 2). The *p* value was calculated for each peak *x* using *t*-test function of two-sample assuming unequal variances in Excel (ver. 16.46). The significant threshold of 0.05 in *p* value was used to determine the equivalence of relative peak heights. The equation for relative peak intensity is described as follows.

$$Rel.Int.\_{\mathbf{x}} = 100 \times I\_{\mathbf{x}} / I\_{Thr-d} \tag{3}$$
