This study presents the derivation and validation of a model that permits simulation of interfacial species transfer in rectification and absorption processes in the context of the algebraic Volume-of-Fluid (VoF) approach. The model is based on the Continuous Species Transfer (CST) method introduced by Marschall et al. (2012) and Deising et al. (2016), which is generalised in such a way that not only absorption but also rectification can be simulated, and is therefore termed Generalised Continuous Species Transfer (GCST) model. After briefly setting out the motivation of this generalisation, the derivation of the model is outlined, which is followed by its validation.