# Detection of Azo Dyes in Curry Powder Using a 1064-nm Dispersive Point-Scan Raman System
## 3 Results and Discussion
### Detection of Metanil Yellow in Curry Powder  
Figure 7a shows the hyperspectral Raman images of curry powder-metanil yellow mixture samples at 1147 cm\({}^{-1}\) and 1437 cm\({}^{-1}\) across five concentration levels. The 1147 cm\({}^{-1}\) and 1437 cm\({}^{-1}\) are the highest intensity metanil yellow peaks. The peak intensity of metanil yellow was found to be higher than curry powder peak intensity at 1147 cm\({}^{-1}\) and 1437 cm\({}^{-1}\). Intensity threshold value of 525 was selected based on pixel-by-pixel analysis of all spectral pixels to obtain binary detection images. All the pixels with intensities below 525 were converted to background pixels. The remaining pixels represent the metanil yellow pixels. Figure 7b shows the 1147 cm\({}^{-1}\) and 1437 cm\({}^{-1}\) binary detection  
Figure 5: Raman spectra of detected Sudan-I pixels at five concentrations.  
Figure 6: Relationship between Sudan-I concentration in samples and percentage of detected pixels in 1593 cm\({}^{-1}\) binary images.  
images of samples at five concentrations. The white pixels are scattered throughout the sample surface. The number of white pixels is low in the 1% metanil yellow image, and progressively increases in the 3%, 5%, 7%, and 10% concentration images. A gradual increase in the white pixels from the 1% to 10% image indicates more metanil yellow particles were detected at increasing concentrations. A total of 9, 21, 30, 43, and 57 metanil yellow pixels were detected in the 1147 cm\({}^{-1}\) binary detection images of 1%, 3%, 5%, 7%, and 10% concentration samples. Similarly, 9, 22, 28, 43, and 55 metanil yellow pixels were detected in the 1437 cm\({}^{-1}\) binary detection images of 1%, 3%, 5%, 7%, and 10% concentration samples. The metanil yellow pixels have similar spatial distribution in both the binary images. Figure 8 shows the Raman spectra of detected metanil yellow pixels at 1%, 3%, 5%, 7%, and 10% concentration samples. In the figure, the 10% metanil yellow consists of 57 spectra, while the 1% metanil yellow consists of 9 spectra.  
The progressive increase in the detected metanil yellow pixels (Figure 7b) indicates that the percentage of detected pixels and sample concentration are correlated. The percentage of the detected metanil yellow pixels are linearly correlated with the metanil yellow concentration in the samples, with a correlation coefficient of 0.99 (Figure 9).  
The number of detected metanil yellow pixels (Figure 7b) is less than that of Sudan-I (Figure 4b) for the same concentration. One of the reasons for this discrepancy can be the bulk density of the two  
Figure 7: (a) Hyperspectral Raman images of curry powder-metanil yellow mixture samples; (b) binary detection images at 1147 cm\({}^{-1}\) and 1437 cm\({}^{-1}\).  
chemicals. Sudan-I has a bulk density of 0.18 g/cm\({}^{3}\). The bulk density of metanil yellow is 0.33 g/cm\({}^{3}\). Due to the higher density of metanil yellow than Sudan-I, there were fewer metanil yellow particles than Sudan-I particles in the 25 mm \(\times\) 25 mm \(\times\) 1 mm sample volume.