Figure 1.
The pH of ZMB1 containing litmus dye can be measured by UV-Vis absorption spectrophotometry by cuvette
(A) Representative image of the color of ZMB1 solutions over a pH range that spans from blue at pH 10.11 (left-side) to red at pH 2.14 (right-side).
(B) Plot of the measured pH for a series of ZMB1 calibrator solutions that were prepared at different ratios of ZMB1 acidic (pH 2) and basic (pH 10) stock solutions.
(C) UV-Vis absorption spectrum for the pH-sensitive litmus dye produced over a range of pHs. The isosbestic point – a wavelength where the light absorption of an indicator dye is independent of solution pH – for litmus (520 nm) is indicated by an arrow in the plot. The wavelength of maximum light absorption, or the lambda max (λmax), is indicated with a separate arrow at 590 nm.
(D) The Calibration Curve was fit using the referenced Python code for sigmoid-based calibration curve fitting with the absorption ratio (Abs590 nm / Abs520 nm) plotted as a function of solution pH.