<p>In this practical project, preconcentration and quantitation of N-nitrosodiethanolamine from wastewater were done by the mode of microextraction named vortex-assisted inverted dispersive liquid–liquid microextraction (VA-IDLLME) method and high-performance liquid chromatography (HPLC) apparatus, photolysis and post-column derivatization process. Several parameters were predicted to be effective in extraction and recovery efficiency. The most critical factors included the type and volume of extracting and dispersing solvents, solution pH, stirring speed, extraction time, and the presence and concentration of salt. All these factors were systematically studied and optimized. Optimum extraction parameters are 150 µL dodecane as extracting solvent, 400 µL methanol as dispersing solvent, pH = 9 for the solution, stirring speed: 500 rpm, without the effect of extraction time and negative impact of NaCl concentration. At the above optimal conditions, a linear range for N-nitrosodiethanolamine determination by HPLC after photolysis and post-column derivatization was 1.0–1500.0 ng mL⁻¹ (R² = 0.9995). The detection limit, extraction recovery, and preconcentration factor were 0.42 ng mL⁻¹, 88%, and 108, respectively.</p>