Digital colorimetric detection of ammonium in water samples after microextraction procedure using deep eutectic solvent, based on DLLME method

In this study, we have presented a simple, cost-effective, and efficient method for quantifying ammonium ions based on digital colorimetry using a smartphone. Firstly, ammonium ions are converted into a yellow-colored derivative in an alkaline medium in the presence of acetylacetone and formaldehyde. Then, the colored compound is extracted using the dispersive liquid–liquid microextraction (DLLME) technique and its color intensity was measured using a smartphone as RGB Color Detector. For this purpose, a novel deep green eutectic solvent including tetrapropylammonium bromide (TPABr) and 3-methyl-1-butanol (isoamyl alcohol) was employed, with a molar ratio of 1:6. The impact of key variables on the derivatization and microextraction processes, including solution pH, concentration of acetylacetone and formaldehyde, temperature, reaction time, and extraction solvent volume, was thoroughly investigated and optimized. In the optimized conditions, the method was found to be linear in the range of 0.15–5.00 µg mL−1 with a limit of detection of 0.05 µg mL−1 (S/N = 3). Moreover, the proposed method was successfully applied for the determination of ammonium ions in environmental water samples, fish pond, and aquarium water samples, with recoveries ranging from 94.7 to 106.7 %.