Vibrational structure of the polyunsaturated fatty acids eicosapentaenoic acid and arachidonic acid studied by infrared spectroscopy

The spectroscopic discrimination of the two structurally similar polyunsaturated C20 fatty acids (PUFAs) 5,8,11,14,17-eicosapentaenoic acid and 5,8,11,14-eicosatetraenoic acid (arachidonic acid) is shown. For this purpose their vibrational structures are studied by means of attenuated total reflection (ATR) Fourier-transform infrared (FT-IR) spectroscopy. The fingerprint regions of the recorded spectra are found to be almost identical, while the C–H stretching mode regions around 3000 cm−1 show such significant differences as results of electronic and molecular structure alterations based on the different degree of saturation that both fatty acids can be clearly distinguished from each other.