Harnessing pH indicators for timely detection of ammonia

Abstract

Ammonia, a crucial marker compound released from land-applied manure, and spoiled foods, holds a distinctive odor and causes potential health hazards. Existing detection methods for ammonia have practical drawbacks, particularly for commercial applications. Commonly used Nessler reagent comprises mercury ions, poses significant environmental and health risks, and requires careful handling and disposal procedures. These limitations highlight a timely need for an alternative point of detection method that consists of reliable and practical ammonia detection. Entrapping the pH indicator into a Sol-Gel matrix is an alternative for ammonia detection. The Sol-gel matrix was prepared using Tetraethoxysilane (TEOS), Methanol, Sodium dodecyl sulfate, and HCl solution. TEOS serves as a silica precursor, facilitating the formation of a stable and porous Sol-Gel matrix. Bromothymol Blue was used as the pH indicator which was entrapped into the Sol-Gel matrix during the preparation. The Sol-Gel solution was kept for a week until it became a solid disk. Once the disks were prepared, each disk was exposed to known ammonia concentrations (0.1M – 1.0M) within a particular time period to measure the color changes. The original color of the disk was yellow, and it changed to blue after the interaction with ammonia. The Color Changes corresponding to the ammonia concentrations were captured and RGB Values were determined by Image J software. Using (R+G+B)/3 formula, a graph was plotted in correlation with the ammonia concentration. Equation y = -(26.608) x + 166.49 was derived and the disk’s sensitivity was equated to the ‘m’ value of 26.608. R2 was calculated using the equation where R2 = 0.99. The lowest detectable ammonia concentration was found to be 0.1M as beyond this limit didn’t result in significant color changes.