Recent advances in microfluidics have made it possible to carry out expensive tests on a small chip [1]. In this context, the use of smartphones as mainly colorimetric detectors has provided the promise of complete transfer of the analytical chemistry process from sample preparation to detection on microfluidic chips [2]. In this research, a microfluidic chip has been used as a platform for the extraction and smartphone-enabled colorimetric measurement of N- acetylcysteine. The extraction phase was a deep eutectic solvent based on 1,10-phenanthroline and thymol with a ratio of 2:1. Analyte determination was done indirectly in this work. N- acetylcysteine reduces Fe3+ ions to Fe2+ on the chip, and the produced Fe2+ selectively forms a red-orange complex with 1,10-phenanthroline in the extraction deep eutectic solvent phase. The results showed that the amount of red color in the extraction phase depends directly on the analyte concentration. In this way, it was possible to measure N-acetylcysteine in the concentration range of 9.0 ppb to 0.5 ppm. The calibration curve was bilinear and the sensitivity of the method was better at the lower concentrations (lower concentration range slope: 29.812, higher concentration range slope: 9.627). The method's detection limit was 3.0 ppb and the quantification limit was 9.0 ppb. The method was validated after evaluating the effect of possible interferences in the water and plasma matrix. The results showed that the method provides high accuracy (recovery percentage: 96.6-107.5%) and precision (coefficient of variation: 0.46-1.90%) for determining N-acetylcysteine in plasma and water samples.
