LAUSR

Abstract This paper presents a near-infrared imaging method to measure the concentrations of acid (HCl and H2SO4), base (NaOH), and produced salt (NaCl and Na2SO4) simultaneously during neutralization in a microfluidic channel. This method is based on spectral variations in the water absorption band observed in the wavelength range 1350–1600 nm. Linear correlation models using three characteristic wavelengths in the band are constructed to convert the absorbance to the concentrations. The images clearly show that at the interface between the acid and base solution streams, the concentrations decrease and salt is produced, diffusing in the transverse direction. The concentration range is 0–2 mol/L and the resolution is