The transformation process used to turn glass tubing into a finished article, causes an inevitable increase of surface alkalinity. A study was designed to quantify and distinguish the endogenous contribution of the tubing from other contributions arising from the conversion process. A representative sample was selected from a segregated pallet provided by one supplier, tubing was cut into pieces of suitable length in a way that their surface to volume ratio was of the same order as the cartridges obtained from the same tubing. One end of the pieces were closed with stoppers, the pieces were subject to suitable testing to identify the alkali and other water soluble glass species which are readily available on the inner surface of the raw tubing. Other tests were carried out to isolate the contribution of the autoclaving process and to estimate the total contribution of the glass as a material before being processed on the conversion line. Extracts were analysed by ICP-OES; the results indicated that a significant amount of alkali could be extracted by simple rinsing and much more during the autoclaving state. Two main contributions were identified, the inner surface of glass tubing as received and the annealing stage, while other contributions from critical steps identified during the conversion process were found to be negligible. It was concluded that the surface state of the tubing as received is a key factor in controlling the alkali release, while the contribution of the annealing stage to the final Na2O release can be estimated to be about 20-25% of the raw material contribution. The method shows good reproducibility and appears to be reliable for predicting before the conversion process whether the finished cartridges will meet the specifications requested by the pharmaceutical companies.
