North American Sterilization & Packaging Company
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(Continued from Page 6, IR Spectroscopy)

Speeding EtO-Sterilized Products to Market with Parametric Release (continued)

IR Spectroscopy for Gas Diffusion

EtO sterilization has traditionally taken place in stainless-steel, vacuum-pressure vessels with extensive ancillary equipment. However, for more than 25 years there has been a less costly and more flexible alternative to these fixed-volume steel vessels. This method, known as gas diffusion, can also be confirmed with parametric release by using IR spectroscopy to measure the gases.

In gas diffusion, liquid EtO is vaporized directly into a low-density polyethylene (LDPE) bag that contains several finished devices, each in individual sterile-barrier packaging. Placed in a heated room or container, the EtO penetrates each sterile barrier, sterilizing the devices. With time, the EtO diffuses across the LDPE and out of the package. This sterilization method precisely delivers gases to within centimeters of each device.

Typically, BIs are used with gas diffusion in accordance with the ANSI/AAMI/ISO 11135-1994 sterilization standard. However, as mentioned previously, they make the process more expensive and time-consuming.

An IR beam can cross multiple layers of transparent LDPE without interference and without danger to the contents of the bag. Avoiding physical invasion of the sterile device packaging during gas analysis means that any number of packages can be held in the IR beam for confirmation of their water vapor and EtO contents without sacrificing a single sample. The use of either GC or BIs requires the sterile barrier to be compromised to obtain results.

Figure 2. Diagram showing basic components and gas flow of a nondispersive infrared gas analyzer. (Diagram courtesy of Spectros Instruments, Inc.)

To use IR spectroscopy on an LDPE sterilizer bag, a device must be constructed to hold the IR source and detector at a fixed distance so that packaged products can be placed in the beam path. With this system, accurate analysis of gas content can be achieved in seconds. In one experiment, for example, the IR spectra of EtO, water vapor, and three different types of LDPE bags were measured. The goal was to verify the ability to analyze the contents of an LDPE bag without piercing it. The results demonstrated that LDPE poses no interference to the beam, and that the bands for EtO and water vapor are clearly identifiable (see Figure 3).

For device manufacturers who require EtO sterilization on-site but cannot install the traditional vacuum vessels, or who seek a level of accuracy and process control that is not possible with industrial vessels, IR spectroscopy and the current ISO-compatible EtO sterilization standard allow parametric release following gas diffusion sterilization.

Figure 3. Infrared spectral analyses of water vapor, EtO, and three different types of LDPE sterilization bags. (LDPE sterilization bags courtesy of H. W. Andersen Products, Inc. Spectral analyses courtesy of Nicolet Analytical, Inc.)

With gas diffusion, instead of just over gassing the headspace of a large vessel and then verifying the success of the cycle through incubation of 20 or more BIs, a manufacturer can realistically verify the gas concentration at a statistically significant number of product sites. For the most demanding sterilization protocols, a manufacturer can analyze every product to confirm proper levels of sterilant and water vapor. Once the proper amount of EtO per product is determined through process validation, EtO residuals can also be controlled, protecting the environment, the worker, and, ultimately, the patient.

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