Ethylene oxide, in sterilization

Gramiccioni et al. [187] reported the determination of residual ethylene oxide in sterilized polypropylene syringes and in materials such as plasticized PVC, polyurethane, and para rubber. The sterilized object was cut into small pieces, weighed, and placed into a flask containing N,N-dimethylacetamide (DMA). The flask was capped and shaken to make the sample homogeneous. After 24 hr it was shaken again and a sample was... 

L. Gramiccioni, M. Milana, and S. DiMarzio, A head space gas chromatographic method for the determination of traces of ethylene oxide in sterilized medical devices, Microchem. J., 32 89-93 (1985). 

Kolb and Pospisil [202] have shown that quantitative results can be obtained after several extractions because the extraction follows an exponential relationship. This approach has been termed discontinuous gas extraction. These workers determined the amount of ethylene oxide in a sample of sterilized gloves. Volatiles were chromatographed on a Chromosorb 102, 60-80 mesh column using a flame-ionization detector. A typical chromatogram is shown in Figure 4.6. The calculated amount of ethylene oxide (four extractions) was 5.4 ppm. 

Other Uses of Ethylene Oxide. About 2 percent of ethylene oxide is consumed in miscellaneous applications, such as its use as a raw material in manufacture of choline, ethylene chlorohydrin, hydroxyethyl starch, and hydrox-yethyl cellulose and its direct use as a fumigant/ sterilant. Production of 1,3-propanediol via hydroformylation of ethylene oxide was begun on a commercial scale in 1999. 1,3-Propanediol is a raw material for polytrimethylene terephthalate, which finds uses in fibers, injection molding, and in film. Use of ethylene oxide in making 1,3-propanediol is expected to be as much as 185 million lb by 2004, up from 12 million lb in 1999. 

Occupational exposure of sterilizing staff to ethylene oxide in hospitals, tissue banks, and research facilities can result during any of the following operations and conditions (1) ... 

The significance of this model is that it describes the optimal situation for water permeation into the spore and therefore ethylene oxide permeation to its target site as a function of the moisture content of the spore and the relative humidity of the environment during exposure. The rate of microbial inactivation therefore increases (as long as all other factors are held constant) with increased relative humidity during exposure. Kaye and Phillips [4] demonstrated a 33% RH optimum for microbial inactivation as a result of exposure to ethylene oxide. In practical situations it is better to err on the side of too much rather than too little moisture. With industrial-scale ethylene oxide sterilization, humidity levels are usually in the range of 50% to 60% RH. The upper limit is usually dictated by deleterious effects on packaging. 

The second indirect method is by measurement of the weight of ethylene oxide delivered from the feed containers to the sterilizer. This method assumes no leakage, liquefaction, or polymerization of ethylene oxide in the gas tines connecting the gas source to the sterilizer. It is recommended that the two indirect methods be used in conjunction with each other. The weight loss method ensures that the increase in pressure is in fact due to gas from the ethylene oxide feed container and not from diluent gas or some other source whereas the pressure method provides an ongoing index of gas concentration during the exposure period. Gas makeups should be automated and specified to be drawn from the ethylene oxide feed tanks, not from the diluent gas. Gas makeup may be controlled by pressure switches or by pressure transducers connected to solenoid valves controlling gas flow. 

The amount of residual ethylene oxide in a product can be signiflcantly influenced by sterilization process conditions. Gas concentrations and exposure times within the exposure period of the cycle should be sufficient to achieve sterility, but their effects on residues should be considered before prolonging them unnecessarily. Importantly, free gaseous ethylene oxide is easiest to remove from product loads, and this is best addressed by postexposure evacuation and aeration. Multiple evacuarians and forced circulation aeration at temperatures around 30 C have been found to be effective. The effects of increased temperatures extend beyond the removal of the free gas to the removal of other forms of bound ethylene oxide. 

Ernst, R. R. (1973). Ethylene oxide gaseous sterilization for industrial applications. In Industrial Sterilization (G. Briggs Phillips and W. S. Miller, eds.). Durham, N.C. Duke University Press. 

Gamma radiation is growing as an accepted alternative to ethylene oxide sterilization. Although it is cleaner than ethylene oxide in that it does not leave any residue, there is a tendency for resins to discolor or turn yellow. 

The growing concern over the toxicity of residual ethylene oxide after sterilization of polymers for use in the field of medicine has led to the rapid growth of the field of radiation sterilization. The medical industry consumes a massive volume of polymeric material in both equipment and implants. As a consequence there is much interest in the effects of radiation on the physical properties and stability of irradiated polymers. The standard dose for radiation sterilization is 25 kGy, which is sufficient to alter the properties of many polymers, being for example close to or above the gel dose of many elastomers. There is also interest in the reaction of oxygen with long-lived radical species formed during irradiation. A common polymer used in medical equipment, poly(propylcne) is susceptible to oxidative degradation, and must be blended with appropriate stabilizers before radiation sterilization. 

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