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. 2021 Sep;413(23):5695-5702.
doi: 10.1007/s00216-021-03485-3. Epub 2021 Jul 31.

Altering the substituents of salicylic acid to improve Berthelot reaction for ultrasensitive colorimetric detection of ammonium and atmospheric ammonia

Haili Yu #  1 , Guihua Zhang #  1 , Yanhua Cai  2 , Faqin Dong  3
Affiliations

Altering the substituents of salicylic acid to improve Berthelot reaction for ultrasensitive colorimetric detection of ammonium and atmospheric ammonia

Haili Yu et al. Anal Bioanal Chem. 2021 Sep.

Abstract

The Berthelot reaction is a classic method for detection of ammonium (NH4+) and atmospheric ammonia (NH3) by using salicylic acid (SA) as the chromogenic substrate. However, there lacks a method for improving the activity of the Berthelot reaction to enhance the analytical performance for detection of NH4+ and NH3. Here, five SA analogues with electron-withdrawing groups (-F) and electron-donating groups (-CH3 and -OCH3) at different positions of the aromatic ring have been chosen as the alternative to SA for Berthelot reaction. Among these analogues, 4-methoxysalicylic acid (4-OCH3-SA) shows the best colorimetric response and color change at a NH4+ concentration of 30 μM, and the sensitivity of 4-OCH3-SA-based colorimetric assay for NH4+ increases 1.75-fold compared with that of SA-based colorimetric method. This enhancement effect is attributed to the strong electron-donating property of 4-OCH3 group, activating the two-step electrophilic aromatic substitution reaction in the Berthelot reaction. Additionally, visual and sensitive detection of NH3 is realized, along with a low limit of detection down to 0.037 ppm. Furthermore, we demonstrate that this assay is reliable and practical for detection of NH4+ and NH3 in real water and air samples with good accuracy.

Keywords: Ammonium; Atmospheric ammonia; Berthelot reaction; Colorimetric detection; Electronic effect.

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