3234 of electrons of the aniline nitrogen in the chlorosulfoamyl benzoic acid entity on the other hand (38). It is worth noting that whether one deals with either amorphous or crystalline furosemide in the solid or solution, formation of CSA is always preferable than any other option. During the high-impact cryogenic grinding, furose- mide was prone to decompose to CSA. In other words, the cryogrinding provided enough mechanical energy to initiate chemical reaction. Unfortunately, there is no possible experimental way to verify the amount of mechanical energy that was generated and transferred to the ground sample during mechanical treatment under cryogenic conditions. However, based on some very rudimentary theoretical consideration proposed by Delogu et al. (41), we are able to estimate the mechanical energy dose transferred to a sample, i.e. total energy transfer mechanically transferred to the powder over a definite milling time. Of course, this is only an estimation which does not include the effect of cryogenic temperature upon the milling process. On the other hand, it predicts the potential impact of that mechanical device. In the first step, it is necessary to describe the trajectory of the magnetic rod placed in the grinding vessel and vibrated between two poles of an electromagnet. This trajectory is presented in Scheme 2. In our case, it is rather an easy-to- guess path; however, for a cylindrical-shaped traditional ball mill with few balls inside, it might be slightly more complicated (42). By assuming a purely plastic collision, the impact energy generated per hit can be calculated from the following equation: Scheme 2 Typical vessel used for high-impact cryogenic grinding. Adrjanowicz et al. E ¼ mRv2 2 I ¼ E N Dm ¼ E N t mp where mR is the mass of the magnetic rod and v is its velocity. The latter can be calculated knowing specific milling configuration and size of the vessel. The impact energy was found to be E = 1.5 mJ/hit. From impact energy E and frequency N generated per hit, the milling intensity can be determined as (41) This leads to I= 22 mW. The total energy transferred to the powder, known also as the specific milling dose, is given by (41) where mp is the mass of the powder and t refers to the total milling time. Assuming the total mass of the powder as 1 g, our consideration leads to the following values: 6.5, 12.5, and 18.7 kcal/mol for 60, 120 and 180 min of grinding, 1 ð Þ 2 ð Þ 3 ð Þ respectively These values are obviously not high enough to cause decomposition of the drug upon milling, especially because the cryogenic temperature effect was not taken into account. However, one should be aware that during milling the collisions are more likely heterogeneous rather than homogenous. Thus, the energy transfer to each particle wouldn’t be the same. Some of them would receive it more, while others less, and only those entities which received enough energy to overcome activation barrier would be decomposed. As revealed by UPLC studies, just 2.18%, 5.98% and 6.81% out of 1 g of furosemide sample decompose after, respectively, 60, 120 and 180 min of milling. If the specific milling dose is calculated for only such amounts of the powder (according to their total milling time), we obtain that in each case the energy transferred to the samples exceeds more than 200 kcal/mol. These theoretical estimations indicate that the milling is able to generate enough energy to overcome the energy barrier and initiate decomposition of furosemide. However, exper- imental values of total energy transferred to the sample would certainly be lower. We suppose that as the particle