Quantitative aqueous ammonium ion analysis by transmission infrared spectroscopy

Area of Science:

• Analytical Chemistry
• Spectroscopy

Background:

• Ammonium ion (NH4+) quantitation in aqueous solutions is crucial for environmental and industrial monitoring.
• Traditional methods like titration can be time-consuming and less accurate for precise measurements.

Purpose of the Study:

• To evaluate the feasibility of using commercial infrared filter instruments for aqueous ammonium ion quantitation.
• To compare the accuracy of infrared analysis with the micro-Kjeldahl titration method.

Main Methods:

• Infrared spectrophotometry was employed to analyze ammonium salt solutions, identifying key absorption bands.
• A Multispec M1 analyzer was configured with specific filters for dual-wavelength analysis.
• Quantitation was performed using the dual-wavelength method with a reference wavelength of 5.56 microns.

Main Results:

• Two primary absorption bands for ammonium ions were identified at 3.49 microns and 6.89 microns.
• The 6.89 microns band showed a stronger response to NH4+ concentration.
• The infrared method demonstrated a linear response up to 0.6% ammonium sulfate and proved more accurate than titration.

Conclusions:

• Commercial infrared filter instruments, like the Multispec M1, are suitable for accurate ammonium ion quantitation in aqueous solutions.
• The dual-wavelength infrared method provides a reliable and accurate alternative to traditional analytical techniques.
• The method's accuracy was unaffected by pH variations within the 3-8 range.