Detection of ammonia in aquaculture wastewater using mango leaf extract-immobilized paper sensors and smartphone colorimetric analysis

Abstract

This study uses smartphones to introduce a simple, sustainable, eco-friendly colorimetric method for rapid ammonia detection in aquaculture wastewater. The device comprises a paper sensor immobilized with a natural indicator and a sample container. An acidic extract from mango leaf was prepared under optimal conditions: water with a pH of 5.0, a mango leaf powder to solvent ratio of 1:20, and extraction at 80 °C for 10 min. This extract was used to prepare paper sensors by immersing pre-cut Whatman filter papers (No. 1) into the solution. A 20 mL clear glass bottle with a black screw cap served as the sample container. The bottle was filled with an ammonium solution and NaOH. Heating this mixture released ammonia gas. A paper sensor was placed on top of the bottle, which changed color when exposed to the gas. A smartphone, positioned 8 cm above, captured images of the sensor after the color change. These images were then analyzed to determine the ammonia concentration in the samples. The optimal conditions for ammonia detection were determined to be a 10:5 ratio of ammonium to 0.50 M NaOH, a temperature of 60 °C, a 10 min sensor response time, and 1 g of sprayed water on the sensor surface. Under these conditions, the LOD was 0.50 mg L−1, with an LDR of 1.70–10.00 mg L−1. The sensor remained stable for up to 45 days. This method has proven to be highly effective in testing aquaculture wastewater samples, achieving recovery rates of 91 % to 101 %.