Rubber types seal stoppers

To assess unknown incompatibilities it is customary to make a small mix of drug substance with an excipient [54,55], place it in a vial, place a rubber stopper in the vial, and dip the stopper in molten carnauba wax (to render it hermetically sealed). The wax will harden and form a moisture barrier up to 70°C. A list of common excipients characteristic of this type of test is shown in Table 1. At times it is possible to obtain quantitative relationships of... 

The top seal (overseal) may be a small stopper, a modification of a stopper, a disc or a combination-type system. Each normally requires rubber under compression held in position by an aluminium crimped, rolled-on, etc. overseal. The second sealing surface may be glass or plastic. In the case of glass cartridge tubes, these are invariably produced from the tubular or cane glass process, hence suffer from imperfections associated with this shaping process. Plastic cartridges have never proved popular but are available. 

Glass-to-glass unions, lubricated with 72% perchloric acid, seal well and prevent joint freezing arising from the use of sihcon lubricants. Rubber stoppers, tubes, or stopcocks should not be used with perchloric acid due to incompatibility. Repeated exposure of the motor windings to perchloric acid vapor could result in a fire, unless fhe motor is an explosion-proof type. 

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