Indirect Determination of the Hydrogen Index of Small Volume Solutions by Digital Colorimetry

A technique for the indirect determination of the hydrogen index of aqueous solutions of small volumes (ranging from microliters to hundreds of microliters) by digital colorimetry with the use of consumer optical raster imaging devices is proposed. Determining the pH does not require constant color scales or information about the concentration of the acid-base indicator in the solution. A prototype of a handheld pH analyzer, based on a smartphone, is developed for out-of-laboratory applications. The accuracy of the pH determination results is confirmed by the potentiometry and spectrophotometry techniques.