The XAS measurements in the soft X-ray regions were applied to the element-selective analyses of liquid mixtures in a microfluidic flow. The microfluidic cell consists of the T-shaped microfluidics with the width and depth of 50 μm made in PDMS resin and covered by the Si3N4 membrane with a thickness of 100 nm. XAS spectra was measured by detecting fluorescent soft X-rays using a silicon drift detector. In the O Kα fluorescent image of the T-shaped microfluidics, water and pyridine were merged at the center position, and a laminar flow of pyridine and water was clearly observed in the mixed part. From the N K-edge XAS spectra with the spatial resolution of 30 × 30 μm2, the distributions of the molar fractions of pyridine and water near the liquid-liquid interface in the laminar flow have been determined from the energy shifts probed at different geometric positions.
