Concentration measurement for neutralization reaction and estimation of salt production rate using near-infrared spectroscopic imaging

Abstract

For design and evaluation of microfluidic applications, it is important and required to measure concentration distributions of molecules/ions during chemical reactions in microfluidic channels. This paper presents an imaging method of acid-base neutralization reactions, based on the spectral characteristics of the near-infrared absorption band of water. When the aqueous solutions of H₂SO₄ and NaOH flowed side by side in a microfluidic channel, the concentration distributions of H₂SO₄, NaOH, and Na₂SO₄ were measured simultaneously using three wavelengths of 1410, 1450, and 1540 nm in the ν₁ + ν₃ absorption band of water. The obtained images showed the consumption of H₂SO₄ and NaOH, and the production of Na₂SO₄ along the interface between the two solutions. These images enable us to determine the local consumption and production rates.