On-line gas diffusion membrane separation-flow injection analysis with spectrophotometric detection for the automated determination of ammonia nitrogen in complex industrial wastewater

Abstract

The determination of ammonia nitrogen (NH₃–N) in industrial wastewater is often challenged by complex matrix interference, and traditional laboratory analysis cannot provide timely feedback for dynamic process regulation. To address these issues, an automated online gas diffusion membrane separation-flow injection analysis system coupled with salicylate spectrophotometric detection was developed for the rapid determination of NH₃–N in complex industrial wastewater. This method employs a hollow-fiber membrane contactor to selectively separate volatile NH₃ from the complex matrix, effectively eliminating interference. Under optimized conditions, the method exhibited a linear range of 1.0–50.0 mg L⁻¹ (R² = 0.9997), with a limit of detection of 0.22 mg L⁻¹ and limit of quantification of 0.72 mg L⁻¹. Precision was excellent, with relative standard deviations below 3.0%. The system showed a strong anti-interference performance against salinity up to 35, common co-existing ions, and various organic nitrogen compounds. When applied to real industrial wastewater samples from an ammonia-stripping process, the proposed method showed good agreement with the reference salicylate method (HJ 536-2009) and exhibited higher spike recoveries (86.0–96.7%) compared to the reference procedure. With a sample throughput of 14 samples per hour, the developed method offers a rapid, accurate, automated, and practical solution for the high-frequency monitoring of NH₃–N in complex industrial effluents, supporting improved process control and regulatory compliance.