Featured Application: Reliable and rapid analysis of free fatty acid (FFA) in olive oil is possible from the relative intensity ratio of characteristic vibrational modes observed by Raman spectroscopy.Abstract: Free fatty acid (FFA) is one of the most critical parameters for evaluating the quality of olive oil. In this paper, we present a simple and rapid Raman spectroscopy method for analyzing free fatty acid in olive oil. First, FFA degradation of carotenoids in olive oil is confirmed by analyzing the relative intensity of characteristic vibrational modes and introducing an intensity decrease factor. Second, it is demonstrated that the relative intensity ratio of the two characteristic vibrational modes at 1525 cm −1 and 1655 cm −1 presents a good and rapid analysis of FFA content in olive oil; the relative intensity ratio decreases linearly with FFA content. In addition, resonance Raman scattering of carotenoid is discussed, showing that a green laser should be utilized to study FFA in olive oil.
Raman spectroscopy has been applied to study unsaturated fatty acid in edible vegetable oils. The relative intensity ratio of characteristic vibrational bands has been investigated as a function of the content of totally unsaturated fatty acid, polyunsaturated fatty acid, and monounsaturated fatty acid. The results suggest the intensity ratio of 1655 cm −1 to 1440 cm −1 or 1265 cm −1 to 1300 cm −1 , i.e., a characteristic vibrational band correlated with carbon-carbon double bond in acid chain to a vibrational band not correlated with double bond, could be applied for preliminary analysis of the content of polyunsaturated fatty acid or monounsaturated fatty acid, but cannot be used to analyze the content of total unsaturated fatty acid. Additionally, two-dimensional correlation spectroscopy (2DCOS) has been performed on the content dependent Raman spectra. The 2DCOS result is consistent with that by Raman spectroscopy.intensity ratio of 1655 cm −1 to 1440 cm −1 could be further applied for differentiating different types of PUFAs. With further understanding of relative intensity ratios in various types of UFAs and the development of portable Raman systems, our proposed relative Raman intensity analyses method could be of great interest for practical applications of on-site quality evaluation of edible vegetable oils.
Magnonics, an emerging research field, aims to control and manipulate spin waves in magnetic materials and structures. However, the current understanding of spin waves remains quite limited. This review attempts to provide an overview of the anomalous behaviors of spin waves in various types of magnetic materials observed thus far by inelastic light scattering experiments. The anomalously large asymmetry of anti-Stokes to Stokes intensity ratio, broad linewidth, strong resonance effect, unique polarization selection, and abnormal impurity dependence of spin waves are discussed. In addition, the mechanisms of these anomalous behaviors of spin waves are proposed. spectroscopy is applied for studying vibrational properties of materials. However, due to the anomalous behaviors of spin wave scattering comparing with vibrational scattering, Raman spectroscopy study of spin wave is difficult and limited. In this paper, we present a review of anomalous behaviors of spin waves observed by inelastic light scattering experiments, especially by Raman spectroscopy. The large asymmetry of anti-Stokes to Stokes intensity ratio, broad linewidth, strong resonance effect, unique polarization selection, and abnormal impurity dependence of spin waves are discussed, and a proposed model for the mechanisms of spin flip, spin relaxing, and spin wave scattering is presented for understanding these anomalous behaviors of spin waves. In addition, two magnonic crystal structures are proposed for manipulating spin waves through analyses of the abnormal impurity dependence of spin waves. The review of the anomalous behaviors of spin waves and the proposed models provide the directions for easier experimental study of spin waves by inelastic light scattering, which will be useful for raising the research efforts for investigating spin waves. This is important for the emerging research of magnonics, which has received extensive interests in the modern magnetism research community.
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