2.2.2. UATR-FTIR Studies

UATR-FTIR spectroscopy is commonly used as screening technique for assessing the potential physicochemical interaction between an API and the excipients employed in the pharmaceutical dosage forms. Usually, UATR-FTIR spectroscopy is used as a complementary tool along thermal analysis for the evaluation of compatibility/incompatibility between API and excipient, which is kept under ambient conditions.

The disappearance of an absorption band, a reduction of the band intensity, or the appearance of new bands reveal the existence of interactions between the API and the studied excipient [34,55–58]. This method provides information about the chemical groups to avoid in the excipients in order to develop stable pharmaceutical formulations [55].

The UATR-FTIR spectra of the inclusion complex RSP/RM-β-CD and its physical mixtures with selected excipients recorded at ambient temperature are shown in Figure 9.

**Figure 9.** UATR-FTIR spectra of RSP/RM-β-CD inclusion complex and its physical mixtures with selected excipients.

The UATR-FTIR spectrum of RSP/RM-β-CD inclusion complex exhibits a broad band between 3500 and 3300 cm−<sup>1</sup> (peak at 3387 cm−<sup>1</sup> ) related to hydroxyl groups (O-H stretching vibration) and other several bands noticed in Table 1; they are presented in Section 2.1.5.


**Table 1.** UATR-FTIR characteristic bands for RSP/RM-β-CD and its mixtures with excipients.

The spectral data collected in Table 1 along with the spectra depicted in Figure 1 reveal that the characteristic bands of RSP/RM-β-CD are present in the mixture of the KP with excipients either at the same wavenumber as in inclusion complex or slightly shifted to different wavenumbers, except for the case of the physical mixture of KP with LCT, where the spectral bands form 1465 and 1006 cm−<sup>1</sup> have disappeared from the mixture spectrum. This situation indicates an interaction between the inclusion complex and LCT even in ambient conditions, which are results that were previously suggested by the thermoanalytical methods.
