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Glass Standards

USP Types

Various standards govern the classification of glass into types suitable for specific uses. These standards include ASTM (American Society for Testing and Materials), EP (European Pharmacopoeia), and USP (United States Pharmacopoeia).

The following classifications were determined by USP criteria. The applicability of a particular container to an end use cannot be determined by this criteria alone. Other general criteria has been developed to assist with the use of the USP classifications in selecting containers.

USP Type I borosilicate glass is the least reactive glass available for containers. It can be used for all applications and is most commonly used to package water for injection, UN-buffered products, chemicals, sensitive lab samples, and samples requiring sterilization. All lab glass apparatus is generally Type I borosilicate glass. Examples of Type I borosilicate glass include Corning® Pyrex® 7740 and Wheaton 180, 200, and 400. Though Corning® Vycor® 7913 is not classified as a Type I glass, it does meet or exceed USP Type I requirements.

In most cases Type I glass is used to package products which are alkaline or will become alkaline prior to their expiration date. 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 attack under certain conditions. Although Type I borosilicate has the least pH shift of any glass, there still may be some sensitivity with certain packaged products.

Surface treatment is not usually required, however it will further enhance the desirable characteristics of an already superior container. This surface enhancement may become especially important for small containers because of the high ratio of container surface area to the volume of the container contents.

USP Type II de-alkalized soda-lime glass has higher levels of sodium hydroxide and calcium oxide. It is less resistant to leaching than Type I but more resistant than Type III. It can be used for products that remain below pH 7 for their shelf life.

USP Type III soda-lime glass is acceptable in packaging some dry powders which are subsequently dissolved to make solutions or buffers. It is also suitable for packaging liquid formulations that prove to be insensitive to alkali. Type III glass should not be used for products that are to be autoclaved, but can be used in dry heat sterilization. Examples of Type III soda lime glass include Wheaton 800 and 900.

USP Type NP soda-lime glass is a general purpose glass and is used for non-parenteral applications where chemical durability and heat shock are not factors. These containers are frequently used for capsules, tablets and topical products. Examples of Type NP glass include Wheaton 810 and 910.

Factors other than USP Type

1.    The filling processing steps that the container has to withstand are important. If lower thermal expansion of the container is required in the process, several options are available. A typical tubing formed container with thinner and more uniform walls will withstand thermal shock better than a molded glass container in the same expansion range. The physical design of the container also plays a part in the amount of thermal and mechanical shock resistance it exhibits. It is frequently necessary to make a compromise between high resistance to mechanical shock and high resistance to thermal shock.

2.    Light sensitivity: If the products to be packaged are light sensitive, amber glass must be used.

3.    If a product is sensitive to the presence of a particular ion, the composition of the glass container should be considered. For example, if a container was precleaned for environmental sampling and used to test for metal ions, it would not be feasible to measure low levels of metals such as sodium or calcium as the ions are in the container matrix and would eventually bloom back to the surface.

4.    The interaction of glass and aqueous solutions is extremely complex. Extractable and corrosion resistance as well as chemical resistance need to be addressed.