Acid content and buffer-capacity: a charge-balance perspective.

Area of Science:

• Physiological chemistry
• Biophysical chemistry

Background:

• Accurate diagnosis of acid-base disorders necessitates quantitative understanding of acid-base generation and dissipation.
• Quantifying acid content in biological fluids is crucial for this understanding.

Purpose of the Study:

• To demonstrate how the charge-balance model inherently defines pH-dependent buffer capacity.
• To reframe acid transport in physiological terms as a change in the strong ion difference (SID).
• To establish a novel framework for modeling acid balance based on titratable acidity and SID.

Main Methods:

• Utilizing principles of physical chemistry, electroneutrality, and mass conservation.
• Applying Brønsted-Lowry theory to define titratable acidity.
• Developing a novel graphical representation of acid-base status.

Main Results:

• The charge-balance model directly yields pH-dependent buffer capacity.
• Acid transport is equivalent to changes in the strong ion difference (ΔSID).
• Titratable acidity is defined as SID_ref - SID, where SID_ref is the SID at pH 7.4.
• A new framework represents acid-base status as a curve of titratable acidity versus pH, demonstrating path invariance.

Conclusions:

• A unified framework for acid-base modeling is established based on first principles.
• This framework integrates buffer capacity, acid transport, and titratable acidity.
• The model provides a novel method for analyzing acid balance across various biological scales.