Both, experimental investigation of protein adsorption processes and mathematical models describing such processes indicate, that the pH in the absorbent particle might be the key factor for an improved understanding of these chromatographic processes. Thus, a technique aiming at the spatially resolved pH measurement in macroscopic large absorbent particles is presented. The first application of this method, being based on confocal laser scanning microscopy (CLSM), revealed an apparent dependence of the pH calibration curve on the scanning depth. By a model-based approach, factors distorting the measurement signal are identified: The wavelength-dependent light scattering and the re-absorption of emitted light. The resulting consequences for further development and application of CLSM based techniques to measure pH in macroscopic large absorbent particles are illustrated and discussed.