Which diffusion-based ammonia measurement method uses a membrane containing nonactin/monactin?

Which diffusion-based ammonia measurement method uses a membrane containing nonactin/monactin?

• A. Potentiometric/Ion-selective electrode
• B. Colorimetric Nesslerization
• C. Berthelot reaction
• D. Spectrophotometric assay

Answer: (A)

The key idea is using an ammonium-selective ionophore in a diffusion-based sensor. Nonactin (and its monactin form) binds NH4+ selectively within a membrane, so when ammonia diffuses into the sensing layer, NH4+ is captured by the nonactin-containing membrane and a stable potential develops that is proportional to the ammonium activity. This is the hallmark of a potentiometric ion-selective electrode for ammonium, where the signal comes from ion movement across the membrane rather than a color change or spectral measurement. The other methods rely on chemical reactions or colorimetric changes (Nesslerization, Berthelot, or simple spectrophotometric assays) and do not use a diffusion-based membrane with an ammonium-selective ionophore.

The key idea is using an ammonium-selective ionophore in a diffusion-based sensor. Nonactin (and its monactin form) binds NH4+ selectively within a membrane, so when ammonia diffuses into the sensing layer, NH4+ is captured by the nonactin-containing membrane and a stable potential develops that is proportional to the ammonium activity. This is the hallmark of a potentiometric ion-selective electrode for ammonium, where the signal comes from ion movement across the membrane rather than a color change or spectral measurement. The other methods rely on chemical reactions or colorimetric changes (Nesslerization, Berthelot, or simple spectrophotometric assays) and do not use a diffusion-based membrane with an ammonium-selective ionophore.