CA1276533C - Chemical indicator - Google Patents

Abstract

CHEMICAL INDICATOR

Abstract of the Disclosure A chemical indicator for use in an ethylene oxide sterilization process which is made of a paper strip having an indicia imprinted thereon with ethylene oxide sensitive ink. The paper indicator is laminated with plastic films which surround the indicia of three sides, leaving only one edge of the indicia exposed to ethylene oxide gas. When the chemical indicator is exposed to an ethylene oxide environment for sufficient time to sterilize, the indicia changes color, starting at the exposed edge, thereby indicating the extent to which sterilization has been accomplished.

Description

~ ~7~S33 CHEMICAL INDICATOR
Background of the Invention The present invention relates to a chemical indicator for use in ethylene oxide sterilization procedures.
Ethylene oxide indicator strips are used to indicate that an ethylene oxide sterilization procedure has been properly accomplished. A typical ethylene oxide indicator strip, such as that sold by Surgicot, 55 10Kennedy Drive, Smithtown, New York 11787, is printed with an off-white ethylene oxide sensitive ink which turns progressively darker (towards brown) when exposed to progressively longer contact with ethylene oxide gas.
A preprinted colox standard on the indicator strip may be used for comparison with the ink reaction color in order to decide whether the sterilization cycle was long enough and whether the gas was concentrated enough to accomplish the desired sterilization.
Ethylene oxide sterilization is not only a function of exposure time and gas concentration, but it is greatly affected by relative humidity (with the middle ranges of relative humidity, e.g., 60% of relative humidity being optimal). Without adequate moisture, ethylene oxide sterilization may no-t be achieved. Also, the ethylene oxide sensitive inks will fail to turn an adequate shade of brown.
-Since sterilization is a microbial killing -process, all parameters of a sterilization cycle have some bearing upon microbial kill. Manufacturers of chemical indicator strips claim that if the ethylene oxide sensitive ink turns a color which is darker than the preprinted color standard, then the microbes in the vicinity of the indicator strip would have been killed.
However, a user cannot tell how much of a safety margin a particular sterilization cycle produced. A

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i.2 7~i53~3 significant part of the sterilization cycle in a hospital is the safety margin, i.e., the overkill, which indicates the probability of having achieved sterilization.
Summary of the Invention The present invention~ is an ethylene oxide indicator strip comprised of a paper strip printed with an ethylene oxide sensitive ink. The strip is laminated on both surfaces with an ethylene oxide impermeable material, such as polyester. The laminate also covers three edges of the strip leaving the fourth side open to ethylene oxide and moisture penetration. Since the ethylene oxide and moisture cannot penetrate the laminate, during sterilization the gases enter through the open edge causing a color reaction to occur first thxough the open edge and then to migrate deeper with time. Accordingly, the ethylene oxide indicator strip will exhibit a color range which géts progressively darker in the area closest to the open edge, and the dark area migrates deeper into the laminated strip upon continued exposure.
Brief Description_of the Drawin~
In the Drawing:
FIG. l is a front view of the chemical indicator of the present invention before it has undergone ethylene oxide treatment.
FIG. 2 is a front view of the chemical indicator of FIG. l following ethylene oxide treatment; and FIG. 3 is a cross-sectional view of the chemical indicator of the present invention illustrating its laminations.
Detailed Description of the Preferred Embodiment Referring to FIGS. 1-3, the present inventlon is a chemical indicator lO. In the preferred embodiment of the invention, the chemical indicator 10 is a paper strip indicator comprised of a strip of paper 18 ~.2~;33 that is laminated with plastic films 16, 20 ~see FIG. 3) on its top and bottom surfaces, and around three edges 22, 24, 26, but not on one edge 28 which the indicia 14 is exposed to. In the prefe:rred embodiment of the invention, the plastic films 16, 20 used for laminating the chemical indicator 10 are clear or transparent matted plastic. It has been found that a number of plastics may successfully be 11sed as the laminating films; including polypropylene, polyethylene, polyester, and others.
Referring generally to FIGS. 1-2, the paper strip 18 of the indicator 10 is imprinted with a color standard 12 which has a color somewhat darker than the original color of the ethylene oxide sensitive indicia 14 which is imprinted on the chemical indicator 10 (See FIG. 1). Following exposure of the chemical indicator to ethylene oxide, the ethylene oxide-sensitive indicia 14, which was originally lighter in color than the color standard 12, reacts and becomes progressively darker than the color standard 12 ~See FIG. 2), with the darkest portions adjacent the open edge 28. It is desired that after the sterilization procedure, much of the indicia 14 will be darker than the color standard 12, thereby indicating that sterilization has taken place satisfactorily.
The main purpose of the laminating films 16, 20 is to limit the entry of ethylene oxide gas and moisture into the paper strip 18. Accordingly, the physical integrity of the paper strip 18 is preserved and the reactive ink on the indicia 14 does not have an opportunity to be washed out and stain any items being sterilized.
As will be obvious to those skilled in the art, the present invention can be modified in a variety of manners without departing from the spirit or scope of ~.~7~S33 the invention. In particular, the present invention provides a dosimetry function which results from the fact that the ethylene oxide sensitive indicia 14 is exposed to ethylene oxide gas which enters the indicator through the single exposed edge 28. In order to provide the dosimetry function, it is not necessary for the indicia 14 to extend to the open edge 28, but only that the ethylene oxide gas must travel along the indicia 14 from a particular location, thereby darkening the ethylene oxide sensitive ink on the indicia 14 as the exposure time inc-reases. Accordingly, the specific shape of the indicator 10 may be varied without departing from the present invention. By way of example, the indicator could be round and the ethylene oxide sensitive indicia could be circular. In such case, the edges of the indicator could be completely sealed around the circumference of the circle and the opening which exposes the indicia to ethylene oxide can be an opening through the plastic laminate.
Other changes, such as to the writing on the indicator may be changed for particular applications without departing from the scope of the invention.
Similarly, other changes may be made for particular applications.

Claims (5)

1. An ethylene oxide sensitive chemical indicator for use in an ethylene oxide sterilization procedure comprising:
(a) a paper strip which has thereon an indicia which has been imprinted with an ethylene oxide sensitive ink;
(b) upper and lower laminating strips of plastic film which overlie and underlie said paper strip and said indicia, said laminating strips surrounding said paper strip, except at one location, whereby ethylene oxide gas can only enter said laminate through said one location.

2. The ethylene oxide sensitive chemical indicator of Claim 1 wherein said indicia extends to at least one edge of said paper strip and said upper and lower laminating strips of plastic film surround said paper strip, except at one edge to which said indicia extends, whereby ethylene oxide gas can only enter said laminate through said one edge.

3. The ethylene oxide sensitive chemical indicator of Claim 2 wherein said paper strip has four edges and said indicia extends to one of said edges, said remaining edges being surrounded by said plastic laminate.

4. The ethylene oxide sensitive chemical indicator of Claim 3 wherein said paper strip further comprises a color standard printed thereon for use in comparing the color said indicia turns following exposure to said ethylene oxide gas.

5. The ethylene oxide sensitive chemical indicator of Claim 4 wherein said plastic laminate is selected from the group of plastics consisting of polypropylene, polyethylene, and polyester.