A further issue herein considered is peak shape. In fact, after a careful glance of the three peaks illustrated in Fig. 1a, it can be seen thatthe shapes of both the second and third modulated peak are not satisfactory, with both peaks presenting a shoulder on the left side of the base. The asymmetry factor (As) was measured for the third modulated peak at 10% ofits height, and a value of 0.75 was derived. The same parameter was not measured for the second modulated peak because the shoulder is located below the 10% peak height mark.