One limitation of this HOP-RSM model is that it only considers linear relationships between the predictors and Kd. The absence of non-linear and interaction terms means that the model does not account for complex adsorption behaviors, such as synergistic or antagonistic effects between variables. For example, adsorption processes often involve non-linear dependencies on pH and pKa, yet these effects are not captured in the current model. Additionally, the large standard error for some parameters (e.g., pKa: 3224.192) suggests possible overfitting or collinearity among predictors, which could impact the reliability of the estimates.