فهرست نشریات علمی دسترسی آزاد ایران

The increasing emission of ammonia gas from industrial and agricultural activities poses significant risks to human health and the environment, which calls for simple and low‑cost onsite monitoring tools. In this work, a disposable paper‑based colorimetric sensor was fabricated by immobilizing 1,2‑naphthoquinone‑4‑sulfonate (NQS) on filter paper for the semi‑quantitative detection of ammonium after converting to ammonia. The sensing principle relies on the nucleophilic substitution reaction of ammonia with NQS to form a brown derivative, leading to a distinct yellow‑to‑brown color change that can be visually observed and digitally quantified. After exposure of the NQS‑modified strips to the ammonia, digital color images of the paper sensor were recorded under fixed illumination and camera conditions using a smartphone, and the mean intensity of each red, (R) green (G), and blue (B) color channel was extracted by image analysis. Calibration curves constructed for ammonium in the range of 1.0–10.0 mg L⁻¹ and limits of detection of 0.76, 0.73, and 1.28 mg L⁻¹ for R, G, and B, respectively. The sensor was successfully used to determine ammonium in fertilizers as real sample. Due to the stripping the ammonium as ammonia from the aqueous sample, nonvolatile amine containing compounds didn’t interfere in determination of ammonium.