The types of glass used in containers can be determined by USP (United States Pharmacopoeia) criteria but, on it’s own, is generally not enough to choose the appropriate vial. This means that the end user will have to look at the choices and then determine the characteristics of each vial on offer as these can vary between manufacturers. However, the UPS criteria is a pretty good place to start.
USP Type I Borosilicate Glass
This is the least reactive type of glass available for containers. All lab glass apparatus is generally Type I borosilicate glass.
In most cases Type I glass is used to package products which are alkaline or will become alkaline over a period of time. Care must be taken in selecting containers for applications where the pH is very low or very high, as even Type I glass can be subject to a reaction under certain conditions. Although Type I has the highest pH stability of any glass, some substances could still cause the glass to become unstable and contaminate the contents.
Many manufacturers now offer vials which have added surface treatments in order to improve the stability of the glass even further.
USP Type II De-alkalized Soda-Lime Glass
This type of glass has higher levels of sodium hydroxide and calcium oxide than type I. Although it is still quite stable and safe to use with products that remain below pH7, it is not as stable as type I.
USP Type III Soda-Lime Glass
This type of glass could be used for storing dry powder and also liquids which are insensitive to alkali. Type III glass should not be used for products that are to be autoclaved, but is suitable for dry heat sterilization.
USP Type NP soda-lime glass is a general purpose glass and is used for non-parenteral products (to be taken orally or by inhalation) as the vial will not typically be in contact with chemicals or heat. These vials are often used for storing medicines in tablet form.
What else should you consider when choosing a container?
- If light sensitivity of the product is an issue, you may wish to consider using an amber glass container.
- If a product is sensitive to certain chemicals within the glass, you could experience a leakage of these substances into the liquid product and cause contamination.
- The filling and processing stages that the container will have to withstand are important. If you require the container to have minimal thermal expansion, there are a few options open to you. A typical tubular container with thinner and more uniform walls will withstand thermal shock better than a moulded glass container within the same expansion range. The physical design of the container can also be important with regards to the amount of thermal and mechanical shock resistance it shows. You will often be required to make a compromise between resistance to mechanical shock and thermal shock in order to decide on the correct container to use.
- The interaction of glass and liquid solutions is incredibly complex. You will need to consider the risk of corrosion and reaction of the glass when used with certain products.
Please use this information purely as a guide to choosing the appropriate container for your application as each requirement will need evaluating separately.