Rubber absorption preservatives

Rubber closures are also known to absorb materials, including drugs. Absorption of preservatives such as chlorocresol into the rubber closures of injectable formulations has been studied extensively [13]. 

Changing the container of a product from glass to plastic can alter its preservation. The container is as much a part of the formulation as is the product that is placed in it. Equally, adsorption and absorption into rubber closures can be significant, as exemplified by the phenolics (Table 4). 

Table 4 Loss of preservative through absorption into rubber caps...

Rubber closures are also known to absorb materials, including drugs. Absorption of preservatives such as chlorocresol into the rubber closures of injectable formulations has been studied extensively.754 756 Water permeability of rubber closures used in injection vials is considered an important parameter in assessing the closures, but quantitative prediction of water permeability through rubber closures is difficult because the diffusion coefficient of water is dependent on relative humidity.757... 

Natural rubber is susceptible to the absorption of many substances (for example preservatives such as chlorobutanol and phenylmercuric borate). 

Fig. 25. Henry s apparatus. The calibrated absorption tube A was filled with mercury, which rose to its corresponding level in the tube B. Tap a is attached to the water supply tap b is opened to allow mercury to run out and thereby admit a known volume of water at tap a. A measured quantity of gas is admitted in a similar manner. Strong agitation is now applied by means of the joint C, which was a tube of rubber covered with leather. Mercury was meanwhile added at the tube B to preserve the pressure the quantity of mercury so required gave the volume of gas absorbed. By pouring more mercury into the extended tube B, the effect of pressure was measured.

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