Role of condensed water in the solid state stability of enalapril maleate

The physicochemical stability of enalapril maleate was investigated in the presence of fourteen different excipients divided into four different classes.
The attached files contain results that are divided into two chapters:
One) The extent of a drug-excipient interaction by following the chemical stability
Two) Investigation of the water sorption characteristics of the excipients.
The chemical stability of enalapril maleate was followed using HPLC. The water sorption characteristics of the excipients were examined from a humidity range of 0 to 90%RH.
The resulting behavior was sectioned in layers by application of three models: Brunauer-Emmet-Teller (BET), Guggenheim-Andersen-de Boer (GAB) and Young-Nelson models.
The GAB-model was applied using the software Universal analysis software of TA instruments. The BET-constant was calculated and applied in Young-Nelson model
where parameters were determined using a multiple regression technique.