EFHSS Questions and Answers - Question Q00238

Is there a documented scientific or technical justification for the method of "freezer storage" or the "shipping on dry ice" of Ethylene Oxide sterilization residual test samples?

Rod MacDonald
Quality Assurance Manager
Alto Development/A&E Medical Corporation
5206 Asbury Road, PO Box 758
Farmingdale, NJ 07727
732-938-2266 phone
732-938-2399 fax

Dear,

I think the rationale for the shipping on ice of residual ethylene oxide test samples is evident. Degassing of EO from the material is stimulated namely by an increase in temperature. E.g. Rendell-Baker confirmed the value of using 55°C heat to aid in ethylene oxide degassing (Roberts RB, Rendell-Baker L; Aeration after ethylene oxide sterilization. Anaestesia 27; 278-282, 1972). Anyway "almost all EO sorbed by a medical device during sterilization will leave the device when placed in an EO-free environment." (Stetson; Ethylene Oxide degassing of rubber and plastic materials. Anestesiology, V 44, Nr 2, 1976).

Dr Danielle Borrey (AZ St Jan Brugge) pointed my attention on: METHOD 5035A: Closed system purge and trap and extraction for volatile organics in soil and waste samples. (see www.clu-in.com/download/char/5035a_rev1.pdf for the complete text).

Ethylene oxide is one of the compounds appropriate for this sampling technique. Dr Borrey confirmed that the principles of this method could be applied to other kind of samples.

8.3 Sample handling and shipment of the method says:
All samples for volatile analysis should be cooled to approximatively 4°C, packed in appropriate containers, and shipped to the laboratory on ice, as described in the sampling plan. See Appendix A, Secs. 3.0, 7.0, and 8.0 for additional sample handling options.

Appendix A: The collection and preservation of aqueous and solid samples for volatile organic compound (VOC) analysis says in A.1.2 What is sample preservation? (p 33):
Several types of sample preservation are employed in EPA methods. The most common method of preservation is to cool the sample to 4°C. Cooling may be applied to many types of sample matrices, including water, soil, sediments, and solid wastes. The temperature of 4°C is used because it represents the temperature at which pure water exhibits its maximum density, hence its minimum volume. etc.
By lowering the temperature of the sample, many of the physical, chemical, and biological processes that may cause environmental contaminants to leave the sample (e.g., loss of volatiles to the air) are greatly slowed.

A.4.0 Solid materials/cohesive soils and volatile organic compounds (p 44) says:
In most solid materials, VOCs coexist in gaseous and liquid phases, as well as sorbed to the solid particles. The molecular diffusion coefficients of VOCs in the gaseous phase are high enough to allow for immediate volatilization of those VOCs from freshly exposed sample surface, resulting in a loss to the surrounding atmosphere. If the sample matrix is porous, these losses will continue as VOCs below the surface diffuse outward. Furthermore, once the gaseous phase is lost, the dynamic equilibrium between gaseous phase and the liquid and the sorbed VOC phases will result in rapid transformations of the liquid and sorbed VOCs to the gaseous phase, where they can continue to be lost to the atmosphere. (Ref. 4) Thus, the primary goal of preservation is to minimise or eliminate the loss of the compounds of concern through direct volatilization to the atmosphere.

I hope this information helps you a little bit further. Feel free to contact Dr Borrey for further scientific information. Her email address is:

Best regards,
Wim Renders