The inclination of the correlation curve is greater for SILB than for RSLB, suggesting a higher sensitivity of absorbance measurements comparatively to acid value titration for the SILB.
Alternatively, the excitation/emission profile was investigated through the contour maps presented in Figures 4 and 5 for SILB and RSLB, respectively.
Similarly to that observed for SILB, it was possible to observe the appearance of emissions at -425 nm, directly associated with the degradation compounds.
From the emission/excitation contour maps, some candidate wavelengths were selected to monitor the oxidative process of SILB and RSLB, as presented in Figure 6.
Figure 7(a) shows the correlation of fluorescence intensity at 424 nm with acid values for RSLB and SILB, respectively.
The induction periods determined in this work for biodiesels from SILB and RSLB were (0.07 [+ or -] 0.01) h and (1.60 [+ or -] 0.10) h, respectively.
This work showed that the composition of fatty acids was feedstock dependent, with high content of unsaturated fatty acids, principally polyunsaturated in SILB. The high content of unsaturated fatty acids reflects in the transformations undergone by RSLB and SILB carbon chains accused by acid value analysis, UV absorption, and fluorescence analysis.
Alternatively, our results showed that molecular fluorescence spectroscopy can be used for monitoring the degradation stages of the RSLB and SILB according to the linear correlation between the emission at 424 nm and AV.
sativus L., resp.) and (a) acid value, (b) absorbance at 232 nm, and (c) absorbance at 270 nm for SILB and RSLB, respectively.