A New Analytical Method to Quantify Ammonia in Freshwater with a Bulk Acoustic Wave Sensor

Area of Science:

• Analytical Chemistry
• Environmental Science
• Materials Science

Background:

• Accurate ammonia monitoring in freshwater is crucial for environmental and health assessments.
• Existing methods, like the indophenol spectrophotometric method, are time-consuming and involve toxic reagents.
• There is a need for rapid, sensitive, and environmentally friendly ammonia detection techniques.

Purpose of the Study:

• To develop and validate a new analytical method for quantifying ammonia in freshwater using a metalloporphyrin-coated piezoelectric quartz crystal.
• To compare the performance of the new method with the established indophenol spectrophotometric method.
• To assess the potential for simultaneous quantification of ammonia and amines.

Main Methods:

• A 9 MHz quartz crystal was coated with chloro[5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato] manganese(III).
• Ammonia quantification was achieved by measuring the frequency decrease of the coated crystal upon exposure to freshwater samples.
• The new method's results were statistically compared (α = 0.05) with those from the indophenol spectrophotometric method using real-world water samples.

Main Results:

• The piezoelectric sensor enabled ammonia quantification in the range of 5–70 µg L⁻¹ with a sensitivity of 0.60 Hz L µg⁻¹.
• Analysis time was reduced from 1 hour to 2 minutes, with method stability over at least eight months.
• No statistically significant differences in mean or precision were observed compared to the indophenol method.
• The method successfully analyzed turbid samples and eliminated the need for toxic reagents like phenol.
• The sensor demonstrated potential for simultaneous quantification of amines and ammonia.

Conclusions:

• The developed piezoelectric quartz crystal sensor provides a highly sensitive, rapid, and safe alternative for ammonia analysis in freshwater.
• This method offers significant advantages over the traditional indophenol spectrophotometric technique, including reduced sample volume and elimination of hazardous chemicals.
• The technology shows promise for environmental monitoring and potentially for the simultaneous detection of ammonia and related amine compounds.