Coating of glass substrates to prevent alkali ion diffusion into pharmaceutical solutions

We present a coating process to reduce the diffusion of alkali and alkaline earth metals from glass surfaces into aqueous solutions. Our approach is based on the treatment of the glass with (i) (3-aminopropyl)triethoxysilane (APTES) in the first step and (ii) titanium-isopropylate in the second step. The coated glass substrates were characterized using UV/VIS, FTIR, and SEM/EDX analyses as well as water contact angle measurements. Furthermore, the influence of the different coating parameters on the hydrolytic resistance, determined using HCl titration, was investigated. Our results show that with the help of the novel two-step procedure the hydrolytic class of “Type III” glass materials can be increased to “Type II” glass materials according to ISO specification 4802-1:1988 (E).