Dilution-Based Estimation of Intrinsic pH: A Proof-of-Concept in Plant Apoplastic Samples

Accurate determination of apoplastic pH is essential for understanding foliar gas exchange and nutrient transport in plants. However, direct pH measurement in apoplastic fluid is often limited by small sample volumes and technical constraints. We present a simple, dilution-based method to estimate the native pH of apoplastic fluid using the linear relationship between pH and the logarithm of the dilution factor. By extrapolating this relationship, the undiluted pH can be inferred without the need for titration or chemical additives. This approach preserves the sample's native chemical equilibrium and enables robust estimation of pH in microliter-scale extracts. The method also provides an empirical buffer capacity indicator and may offer a practical alternative for apoplastic pH assessment in plant physiological studies.