When CO2 was added to vials containing colorimetric mixeddye-
based indicator solution, a visual color change of the solution
from bright light green to bright red was detected. The most
remarkable change in the absorption spectra after 30 min of reaction
time took place at high absorption peaks in the wavelength
range of 430–526nm (Fig. 2). Bromothymol blue, which shifts from
basic form (blue, pH 7.6) to acidic form (yellow, pH 5.8), results in
maximum lambda (max) shifting from 615–618 to 430–435 nm.
Methyl red, which shifts from basic form (yellow, pH 6.2) to acidic
form (red, pH 4.5), results in maximum lambda (max) shifting
from 430–435 to 523–526nm [22]. As a mixed-dye-based indicator,
bright light green changed to bright red in relation to a
shift in the absorption peak from 430–435 to 523–526nm when
exposed to levels of CO2 from 0% (v/v) to 3.5% (v/v). This vivid color
spectrum of mixed-dye indicator solution is in agreement with Wallach