3.2.3. Blank subtracted RGB values
Methamphetamine pills available in Thailand (sold as Yaba) are
commonly orange in color, but are occasionally white, green, and
blue. These various colors may affect the RGB values of the bluepurple
product. The RGB values of the blank were therefore taken
into account by subtracting them from the RGB values of the
product. Simon’s reagents and the ultrapure water without
methamphetamine standard was used as the blank in this section,
but Yaba extract in ultrapure water without Simon’ reagents was
recommended for illicit sample analysis. The relationships
between the subtracted RGB values and the methamphetamine
concentrations both as individual and total intensities, and their
absorbances are presented in Fig. 6. Both the intensity and
absorbance of the subtracted RGB values increased with increasing
methamphetamine concentration indicating a greater difference
between the color of the blank and the color of the product with
increasing drug concentrations. Red demonstrated the highest
sensitivity echoing the results when the individual RGB values
were considered.