Fourier Transform Infrared Spectroscopy
The principle of Fourier transform infrared spectroscopy (FTIR) is adsorption of light in the infrared region of the electromagnetic spectrum by the most molecules of the sample. The resulting spectrum represents the molecular absorption and transmission, creating a molecular fingerprint of the sample with absorption peaks which correspond to the frequencies of vibrations between the bonds of the atoms making up the material (Esfanjani, Jafari, Assadpoor, & Mohammadi, 2015; Sarmento, Ferreira, Veiga, & Ribeiro, 2006). The identification of different materials, determination of the amount of material present in the sample by measuring the size of the peak, determination of number of components in a mixture, and specifying the quality or consistency of a sample are the main advantages of FTIR. Therefore, FTIR can be exerted as a fast and sensitive analytical method to acquire the main information about the characterization of nanoencapsulation systems (Silva, Cerqueira, & Vicente, 2012).
Hosseini et al. (2013) implemented FTIR for analyzing the OEO- loaded—CS NPs by a two-step method, i.e., oil-in-water emulsion and ionic gelation of CS with sodium TPP. They showed that the electrostatic interaction between NH31 groups of CS and phosphoric groups of TPP was formed within the NPs, shifting the peak of amide I (NH2 bending) from 1647 to 1651 cm-1 and appearing new peaks at 1238 (C—O—C stretch) and 1555 cm-1 (amide II) compared to spectra of CS powder (Fig. 10.9Cb). The results showed that there was no interaction between OEO and CS NPs considering the similarity spectra of pure OLE and OEO-loaded CS NPs (Fig. 10.9Cc,d). Besides, the increasing intensity of the CH stretching peak at 2867—2955 cm-1 in spectra of OEO-loaded CS NPs in comparison to CS NPs indicated an increase in the content of ester groups from OEO molecules; therefore, their results confirmed the encapsulation of OEO in CS NPs.