Inner product of RGB unit vectors for detecting color transition: application to feedback-based flow ratiometric titration

The inner product (IP) of RGB unit vectors’ approach for detecting color transition has further been applied to a feedback-based flow ratiometric titration, including nonaqueous titration. While the flow ratio of titrand/titrant containing an indicator was varying, the video image of the merged solution was taken with a digital microscope downstream. The indicator’s color was converted to an RGB unit vector. The change in IP between vectors was used for determining the equivalence point. The concept was successfully applied to the determinations of drug and vinegar samples with reasonable throughput rate (> 18 s/titration) and precision (RSD < 4.4%). Graphical abstract