Indirect Potentiometric pH Detection of Weak Acids with Absolute Quantitation by a Theoretical Approach

Area of Science:

• Analytical Chemistry
• Electrochemistry
• Chromatography

Background:

• Organic acid determination is crucial in various scientific fields.
• Existing methods for organic acid analysis often require complex calibration and can be prone to dilution and dispersion.
• A need exists for rapid, accurate, and calibration-free methods for organic acid quantification.

Purpose of the Study:

• To develop and validate a fast-response potentiometric flow-through pH sensor for organic acid determination.
• To investigate the use of an ammonia permeation device for baseline pH adjustment without solution mixing.
• To achieve absolute quantification of organic acids through theoretical pH calculations, bypassing the need for analyte standards.

Main Methods:

• Ion exclusion chromatography with perchloric acid (HClO4) as the eluent.
• Utilized a potentiometric flow-through pH sensor for analyte detection.
• Employed an ammonia permeation device for precise baseline pH adjustment.

Main Results:

• Achieved an average limit of detection of 0.06 mM for seven target organic acids (S/N = 3).
• Demonstrated universal pH response to organic acids based on ammonia titration, independent of specific acid identity.
• Quantification of analyte concentration was performed via theoretical pH calculation, with predicted standard concentrations within 5% of actual values.
• Results from real sample analysis agreed within 10% error compared to the conventional bromothymol blue (BTB) method.

Conclusions:

• The developed potentiometric flow-through pH sensor system offers a robust method for organic acid determination.
• Absolute quantification without analyte calibration standards is feasible through theoretical pH response calculations.
• The system provides accurate and reliable results comparable to conventional methods, with potential for simplified analytical workflows.