Vapor sterilization using inorganic hydrogen peroxide complexes

An apparatus and process for hydrogen peroxide vapor sterilization of medical instruments and similar devices make use of hydrogen peroxide vapor released from an inorganic hydrogen peroxide complex. The peroxide vapor can be released at room temperature and atmospheric pressure; however, the pressure used can be less than 50 torr and the temperature greater than 86.degree. C. to facilitate the release of hydrogen peroxide vapor. The heating rate can be greater than 5.degree. C. Optionally, a plasma can be used in conjunction with the vapor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an apparatus and process for using hydrogen 
peroxide vapor to sterilize articles such as medical instruments, and more 
particularly to the use of an inorganic hydrogen peroxide complex for such 
a process. 
2. Description of the Related Art 
Medical instruments have traditionally been sterilized using either heat, 
such as is provided by steam, or a chemical, such as formaldehyde or 
ethylene oxide in the gas or vapor state. Each of these methods has 
drawbacks. Many medical devices, such as fiber optic devils, endoscopes, 
power tools, etc. are sensitive to heat, moisture, or both. Formaldehyde 
and ethylene oxide are both toxic gases that pose a potential hazard to 
healthcare workers. Problems with ethylene oxide are particularly severe, 
because its use requires long aeration times to remove the gas from 
articles that have been sterilized. This makes the sterilization cycle 
time undesirably long. In addition, both formaldehyde and ethylene oxide 
require the presence of a substantial amount of moisture in the system. 
Thus, devices to be sterilized must be humidified before the chemical is 
introduced or the chemical and moisture must be introduced simultaneously. 
Moisture plays a role in sterilization with a variety of other chemicals 
in the gas or vapor state, in addition to ethylene oxide and formaldehyde, 
as Table 1. 
TABLE 1 
______________________________________ 
Relative Humidity Requirements 
Literature 
Chemical for Optimal Efficacy 
Reference 
______________________________________ 
Ethylene oxide 
25-50% 1 
Propylene oxide 
25-50% 1 
Ozone 75-90% 2 
Formaldehyde 
&gt;75% 1 
Glutaraldehyde 
80-90% 3 
Chlorine dioxide 
60-80% 4 
Methyl bromide 
40-70% 1 
.beta.-Propiolactone 
&gt;75% 1 
Peracetic acid 
40-80% 5 
______________________________________ 
1. Bruch, C. W. Gaseous Sterilization, Ann. Rev. Microbiology 15:245-262 
(1961). 
2. Janssen, D. W. and Schneider, P. M. Overview of Ethylene Oxide 
Alternative Sterilization Technologies, Zentralsterilisation 1:16-32 
(1993). 
3. Bovallius, A. and Anas, P. SurfaceDecontaminating Action of 
Glutaraldehyde in the GasAerosol Phase. Applied and Environmental 
Microbiology, 129-134 (Aug. 1977). 
4. Knapp, J. E. et al. Chlorine Dioxide As a Gaseous Sterilant, Medical 
Device & Diagnostic Industry, 48-51 (Sept. 1986). 
5. Portner, D. M. and Hoffman, R. K. Sporicidal Effect of Peracetic Acid 
Vapor, Applied Microbiology 16:1782-1785 (1968). 
Sterilization using hydrogen peroxide vapor has been shown to have some 
advantages over other chemical sterilization processes (see, e.g., U.S. 
Pat. Nos. 4,169,123 and 4,169,124), and the combination of hydrogen 
peroxide with a plasma provides additional advantages, as disclosed in 
U.S. Pat. No. 4,643,876. In these disclosures the hydrogen peroxide vapor 
is generated from an aqueous solution of hydrogen peroxide, which ensures 
that there is moisture present in the system. These disclosures, together 
with those summarized in Table 1, teach that moisture is required for 
hydrogen peroxide in the vapor phase to be effective or to exhibit its 
maximum sporicidal activity. However, the use of aqueous solutions of 
hydrogen peroxide to generate hydrogen peroxide vapor for sterilization 
may cause problems. At higher pressures, such as atmospheric pressure, 
excess water in the system can cause condensation. Thus, one must reduce 
the relative humidity in a sterilization enclosure before introducing the 
aqueous hydrogen peroxide vapor. 
The sterilization of articles containing diffusion-restricted areas, such 
as long narrow lumens, presents a special challenge for hydrogen peroxide 
vapor that has been generated from an aqueous solution of hydrogen 
peroxide, because: 
1. Water has a higher vapor pressure than hydrogen peroxide and will 
vaporize faster than hydrogen peroxide from an aqueous solution. 
2. Water has a lower molecular weight than hydrogen peroxide and will 
diffuse faster than hydrogen peroxide in the vapor state. 
Because of this, when an aqueous solution of hydrogen peroxide is 
vaporized, the water reaches the items to be sterilized first and in 
higher concentration. The water vapor therefore becomes a barrier to the 
penetration of hydrogen peroxide vapor into diffusion restricted areas, 
such as small crevices and long narrow lumens. One cannot solve the 
problem by removing water from the aqueous solution and using more 
concentrated hydrogen peroxide, since concentrated solutions of hydrogen 
peroxide, i.e., greater than 65% by weight, can be hazardous, due to the 
oxidizing nature of the solution. 
U.S. Pat. Nos. 4,642,165 and 4,744,951 attempt to solve this problem. The 
former discloses metering small increments of a hydrogen peroxide solution 
onto a heated surface to ensure that each increment is vaporized before 
the next increment is added. Although this helps to eliminate the 
difference in the vapor pressure and volatility between hydrogen peroxide 
and water, it does not address the fact that water diffuses faster than 
hydrogen peroxide in the vapor state. 
The latter patent describes a process for concentrating hydrogen peroxide 
from a relatively dilute solution of hydrogen peroxide and water and 
supplying the concentrated hydrogen peroxide in vapor form to a 
sterilization chamber. The process involves vaporizing a major portion of 
the water from the solution and removing the water vapor produced before 
injecting the concentrated hydrogen peroxide vapor into the sterilization 
chamber. The preferred range for the concentrated hydrogen peroxide 
solution is 50% to 80% by weight. This process has the disadvantage of 
working with solutions that are in the hazardous range; i.e., greater than 
65% hydrogen peroxide, and also does not remove all of the water from the 
vapor state. Since water is still present in the solution, it will 
vaporize first, diffuse faster, and reach the items to be sterilized 
first. This effect will be especially pronounced in long narrow lumens. 
U.S. Pat. No. 4,943,414 discloses a process in which a vessel containing a 
small amount of a vaporizable liquid sterilant solution is attached to a 
lumen, and the sterilant vaporizes and flows directly into the lumen of 
the article as the pressure is reduced during the sterilization cycle. 
This system has the advantage that the water and hydrogen peroxide vapor 
are pulled through the lumen by the pressure differential that exists, 
increasing the sterilization rate for lumens, but it has the disadvantage 
that the vessel needs to be attached to each lumen to be sterilized. In 
addition, water is vaporized faster and precedes the hydrogen peroxide 
vapor into the lumen. 
U.S. Pat. No. 5,008,106 discloses that a substantially anhydrous complex of 
PVP and H.sub.2 O.sub.2 is useful for reducing the microbial content of 
surfaces. The complex, in the form of a fine white powder, is used to form 
antimicrobial solutions, gels, ointments, etc. It can also be applied to 
gauze, cotton swabs, sponges and the like. The H.sub.2 O.sub.2 is released 
upon contact with water present on the surfaces containing the microbes. 
Thus, this method too requires the presence of moisture to effect 
sterilization. 
Certain inorganic hydrogen peroxide complexes have been reported including 
examples within the following classes: alkali metal and ammonium 
carbonates, alkali metal oxalates, alkali metal phosphates, alkali metal 
pyrophosphates, fluorides and hydroxides. U.S.S.R. patent document No. SU 
1681860 (Nikolskaya et al.) discloses that surfaces can be decontaminated, 
although not necessarily sterilized, using ammonium fluoride peroxohydrate 
(NH.sub.4 F.H.sub.2 O.sub.2). However, this inorganic peroxide complex 
provides decontamination only within the very narrow temperature range of 
70.degree.-86.degree. C. Even within this range, decontamination times 
were quite long, requiring at least two hours. Additionally, it is known 
that ammonium fluoride decomposes to ammonia and hydrofluoric acid at 
temperatures above 40.degree. C. Due to its toxicity and reactivity, 
hydrofluoric acid is undesirable in most sterilization systems. Moreover, 
Nikolskaya et al. disclose that despite the release of 90% of its hydrogen 
peroxide at 60.degree. C., NH.sub.4 F.H.sub.2 O.sub.2 is ineffective at 
decontamination of surfaces at this temperature. Thus, it appears that a 
factor other than hydrogen peroxide is responsible for the decontamination 
noted. 
Hydrogen peroxide is capable of forming complexes with both organic and 
inorganic compounds. The binding in these complexes is attributed to 
hydrogen bonding between electron rich functional groups in the complexing 
compound and the peroxide hydrogen. The complexes have been used in 
commercial and industrial applications such as bleaching agents, 
disinfectants, sterilizing agents, oxidizing reagents in organic 
synthesis, and catalysts for free-radical-induced polymerization 
reactions. 
Generally, these types of compounds have been prepared by the 
crystallization of the complex from an aqueous solution. For example, urea 
hydrogen peroxide complex was prepared by Lu et al. (J. Am. Chem. 
Soc.63(1):1507-1513 (1941)) in the liquid phase by adding a solution of 
urea to a solution of hydrogen peroxide and allowing the complex to 
crystallize under the proper conditions. U.S. Pat. No. 2,986,448 describes 
the preparation of sodium carbonate hydrogen peroxide complex by treating 
a saturated aqueous solution of Na.sub.2 CO.sub.3 with a solution of 50 to 
90% H.sub.2 O.sub.2 in a closed cyclic system at 0.degree. to 5.degree. C. 
for 4 to 12 hours. More recently, U.S. Pat. No. 3,870,783 discloses the 
preparation of sodium carbonate hydrogen peroxide complex by reacting 
aqueous solutions of hydrogen peroxide and sodium carbonate in a batch or 
continuous crystallizer. The crystals are separated by filtration or 
centrifugation and the liquors used to produce more sodium carbonate 
solution. Titova et al. (Zhurnal Neorg. Khim., 30:2222-2227, 1985) 
describe the synthesis of potassium carbonate peroxyhydrate (K.sub.2 
CO.sub.3. 3H.sub.2 O.sub.2) by reaction of solid potassium carbonate with 
an aqueous solution of hydrogen peroxide at low temperature followed by 
crystallization of the complex from ethanol. These methods work well for 
peroxide complexes that form stable, crystalline free-flowing products 
from aqueous solution. 
U.S. Pat. Nos. 3,376,110 and 3,480,557 disclose the preparation of a 
complex of hydrogen peroxide with a polymeric N-vinylheterocyclic compound 
(PVP) from aqueous solution. The resultant complexes contained variable 
amounts of hydrogen peroxide and substantial amounts of water. U.S. Pat. 
No. 5,008,093 teaches that free-flowing, stable, substantially anhydrous 
complexes of PVP and H.sub.2 O.sub.2 could be obtained by reacting a 
suspension of PVP and a solution of H.sub.2 O.sub.2 in an anhydrous 
organic solvent like ethyl acetate. More recently, U.S. Pat. No. 5,077,047 
describes a commercial process for producing the PVP-hydrogen peroxide 
product by adding finely divided droplets of a 30% to 80% by weight 
aqueous solution of hydrogen peroxide to a fluidized bed of PVP maintained 
at a temperature of ambient to 60.degree. C. The resultant product was 
found to be a stable, substantially anhydrous, free flowing powder with a 
hydrogen peroxide concentration of 15 to 24%. 
U.S. Pat. No. 5,030,380 describes the preparation of a solid polymeric 
electrolytic complex with hydrogen peroxide by first forming a complex in 
aqueous solution and then drying the reaction product under vacuum or by 
spray drying at a low enough temperature to avoid thermal degradation of 
the product. 
All of these previous methods of preparing hydrogen peroxide complexes use 
solutions of hydrogen peroxide. Either the complex is formed in a solution 
containing hydrogen peroxide or droplets of a hydrogen peroxide solution 
are sprayed onto a fluidized bed of the reactant material. 
Vapor phase and gas phase reactions are well known synthesis methods. For 
example, U.S. Pat. No. 2,812,244 discloses a solid-gas process for 
dehydrogenation, thermal cracking, and demethanation. Fujimoto et al. (J. 
Catalysis, 133:370-382 (1992)) described a vapor-phase carboxylation of 
methanol. Zellers et al. (Anal. Chem., 62:1222-1227 (1990)) discussed the 
reaction of styrene vapor with a square-plannar organoplatinum complex. 
These prior art vapor- and gas-phase reactions, however, were not used to 
form hydrogen peroxide complexes. 
SUMMARY OF THE INVENTION 
One aspect of the present invention relates to an apparatus for hydrogen 
peroxide sterilization of an article. This apparatus includes a container 
for holding the article to be sterilized at a pressure of less than 50 
torr. Preferably, the pressure is less than 20 torr, and more preferably 
less than 10 torr. The apparatus also includes a source of hydrogen 
peroxide vapor in fluid communication with the container. The source 
includes an inorganic hydrogen peroxide complex at a temperature greater 
than 86.degree. C., and is configured so that the peroxide vapor can 
contact the article to effect sterilization. The source can be located 
within the container, or alternatively, the apparatus can include an 
enclosure disposed outside of the container in which the complex is 
located, and an inlet providing fluid communication betweeen the container 
and the enclosure, such that vapor released from the complex travels along 
the inlet and into the container to effect sterilization. The inorganic 
hydrogen peroxide complex can be a complex of sodium carbonate, potassium 
pyrophosphate or potassium oxalate. Preferably, the apparatus, also 
includes a heater located within the container, whereby the complex is 
placed on the heater and heated to facilitate the release of the vapor 
from the complex. Such a heater can be heated prior to contacting with the 
complex. The apparatus can also include a vacuum pump in fluid 
communication with the container for evacuating the container. In some 
embodiments, the apparatus includes an electrode adapated to generate a 
plasma around the article. Such an electrode can be inside the container, 
or can be spaced apart from the container and adapated to flow plasma 
generated thereby towards and around the article. In a preferred 
embodiment, the complex is in a solid phase. 
Another aspect of the present invention relates to a method for hydrogen 
peroxide vapor sterilization of an article. This method includes placing 
the article into a container, and contacting the article with a hydrogen 
peroxide vapor released from an inorganic hydrogen peroxide complex by 
heating the complex at a rate of at least 5.degree. C./minute to contact 
and sterilize the article. Preferably, the heating rate is at least 
10.degree. C./minute, more preferably, at least 50.degree. C./minute, and 
still more preferably at least 1000.degree. C./minute. The complex 
preferably has less than 10% water. The complex can be heated, preferably 
to a temperature greater than 86.degree. C. to facilitate the release of 
the vapor from the complex. The container can be evacuated before 
introducing the vapor into the container at a pressure of less than 50 
torr, more preferably less than 20 torr, and still more preferably less 
than 10 torr. Optionally, a plasma can be generated around the article 
after introducing the vapor into the container. The plasma can be 
generated either inside or outside of the container. The present invention 
also includes a method for hydrogen peroxide vapor sterilization of an 
article in which the inorganic hydrogen peroxide complex used is one which 
does not decompose to release a hydrohalic acid. 
Yet another aspect of the present invention relates to a method for 
hydrogen peroxide sterilization of an article using a self-sterilizing 
enclosure. In this method, the article is placed in a enclosure containing 
an inorganic hydrogen peroxide complex, the enclosure is sealed, and the 
enclosure allowed to stand at a temperature below 70.degree. C. for a time 
sufficient to release hydrogen peroxide vapor from the complex and effect 
sterilization of the article. Although not necessary, the enclosure can be 
allowed to stand at a pressure less than atmospheric pressure or at a 
temperature above room temperature (23.degree.C.). Thus, the enclosure can 
be allowed to stand at a temperature below about 40.degree. C. Any of a 
variety of enclosures can be used, e.g. a pouch, a container, a chamber or 
a room. Preferably, the hydrogen peroxide complex is in the form of a 
powder or tablet. The sealing step can include sealing the enclosure with 
a gas permeable material, such as TYVEK.TM., CSR wrap, or paper. 
The present invention also relates to a sealed enclosure containing a 
sterile product and an inorganic hydrogen peroxide complex capable of 
releasing hydrogen peroxide vapor. 
Included within the present invention is also a potassium pyrophosphate 
hydrogen peroxide complex. 
A further aspect of the invention relates to a method for hydrogen peroxide 
sterilization of an article having an exterior and a narrow lumen therein. 
This method involves connecting a vessel containing an inorganic peroxide 
complex to the lumen of the article, placing the article within a 
container, whereby the vessel remains connected to the lumen, reducing the 
pressure within the container, and contacting the lumen of the article 
with hydrogen peroxide vapor released from the inorganic peroxide complex 
at a temperature less than 70.degree. C.

DETAILED DESCRIPTION OF THE INVENTION 
Hydrogen peroxide sterilizers that have been used in the past invariably 
used an aqueous solution of hydrogen peroxide as their source of 
sterilant. These sterilizers have disadvantages caused by the presence of 
water in the system. At higher pressure, such as atmospheric pressure, the 
excess water in the system can cause condensation. This requires that an 
extra step be performed to reduce the relative humidity of the atmosphere 
in an enclosure to be sterilized to an acceptable level before the aqueous 
hydrogen peroxide vapor is introduced. These sterilizers also have 
drawbacks caused by the facts that water, having a higher vapor pressure, 
vaporizes more quickly than hydrogen peroxide from an aqueous solution; 
and water, having a lower molecular weight, diffuses faster than hydrogen 
peroxide. When a medical device or the like is enclosed in a sterilizer, 
the initial sterilant that reaches the device from the hydrogen peroxide 
source is diluted in comparison to the concentration of the source. The 
dilute sterilant can be a barrier to sterilant that arrives later, 
particularly if the device being sterilized is an article, such as an 
endoscope, that has narrow lumens. Using a concentrated solution of 
hydrogen peroxide as the source in an attempt to overcome these drawbacks 
is unsatisfactory, because such solutions are hazardous. 
In the present invention, the shortcomings of hydrogen peroxide sterilizers 
of the prior art are overcome by using a substantially non-aqueous (i.e., 
substantially anhydrous) source of hydrogen peroxide which releases a 
substantially non-aqueous hydrogen peroxide vapor. In a preferred 
embodiment, the substantially non-aqueous hydrogen peroxide vapor is 
produced directly from a substantially nonaqueous hydrogen peroxide 
complex. However, the substantially non-aqueous hydrogen peroxide vapor 
can also be generated from an aqueous complex which is processed during 
vaporization to remove water, such as under vacuum. Thus, where an aqueous 
hydrogen peroxide complex is used, the aqueous complex can be converted to 
a substantially non-aqueous hydrogen peroxide complex while carrying out 
the process of the present invention. Preferably, the substantially 
non-aqueous hydrogen peroxide complexes contain less than about 20% water, 
more preferably no more than about 10% water, still more preferably no 
more than about 5% water, and most preferably no more than about 2% water. 
As is apparent from the preferred percentages of water in the substantially 
non-aqueous hydrogen peroxide complexes used in the present invention, as 
provided above, the most preferred hydrogen peroxide complex and the 
peroxide vapor generated therefrom are substantially water-free. 
Nevertheless, as is also apparent from these figures, some water can be 
present in the system. Some of this water may derive from the 
decomposition of hydrogen peroxide to form water and oxygen as byproducts 
and some hydrogen binding of this water to the complex can occur. 
The effect of water was measured in a series of tests, with a sterilization 
chamber maintained at various relative humidities. Test conditions were 
those described in Example 1, below, with spores supported on stainless 
steel (SS) blades in 3 mm.times.50 cm stainless steel lumens. As shown in 
Table 2, under the test conditions, 5% relative humidity has no effect on 
efficacy but 10% relative humidity decreases the sterilization rate. This 
example shows that small amounts of moisture can be allowed in the system 
with the hydrogen peroxide generated from the non-aqueous peroxide complex 
and the presence of water in the system can be overcome by increasing the 
exposure time. 
TABLE 2 
______________________________________ 
Effects of Relative Humidity on Efficacy 
SS Blades in 3 mm .times. 50 cm SS Lumens 
Sterility Results (Positive/Samples) 
Diffusion Time 
1% RH 5% RH 10% RH 
______________________________________ 
5 0/3 0/3 3/3 
10 0/3 0/3 2/3 
15 0/3 0/3 0/3 
30 0/3 0/3 0/3 
______________________________________ 
A primary criterion for the composition of the hydrogen peroxide source is 
the relationship between its stability and hydrogen peroxide evaporation 
rate as a function of temperature and pressure. Depending on the 
parameters of the sterilization process--e.g. pressure, temperature, 
etc.--a higher or lower peroxide evaporation rate may be preferred, and 
heating the peroxide source may or may not be required. The need for 
heating of the peroxide complex depends on the vapor pressure of the 
complex. Some peroxide complexes have a sufficiently high vapor pressure 
that a significant amount of hydrogen peroxide vapor can be released 
without heating the complex. In general, heating the complex increases the 
vapor pressure of hydrogen peroxide and accelerates the release of 
peroxide from the complex. 
To provide a desirably high evaporation rate, the source should preferably 
have a large surface area. Thus the source may be a fine powder or a 
coating on a material that has a large surface area. Of course, safety, 
availability, and cost of the material are also important criteria. The 
release of hydrogen peroxide from hydrogen peroxide complexes with urea, 
polyvinylpyrrolidone, nylon-6, glycine anhydride, and 1,3 dimethyl urea 
were evaluated. The complexes of hydrogen peroxide with urea, 
polyvinylpyrrolidone, nylon-6, and glycine anhydride are solids. The 1,3 
dimethyl urea peroxide complex is a liquid. The glycine anhydride hydrogen 
peroxide complex is a less stable complex under reduced pressure than the 
other complexes evaluated, and under vacuum conditions, most of the 
hydrogen peroxide can be released from the complex without the need for 
additional heating. 
Urea hydrogen peroxide complex is available in tablet form from Fluka 
Chemical Corp., Ronkonkoma, N.Y. and in powder form from Aldrich Chemical 
Co., Milwaukee, Wis. This complex is also known as urea peroxide, hydrogen 
peroxide urea complex, peroxide urea, peroxide urea adduct, urea peroxide 
adduct, percarbamide, carbamide perhydrate, and carbamide peroxide. As 
used herein, the term "urea peroxide" encompasses all of the foregoing 
terms. 
The polyvinylpyrrolidone-hydrogen peroxide complex (PVP-H.sub.2 O.sub.2) 
can be prepared by the method disclosed in International Application Pub. 
No. WO 92/17158. Alternatively, the complexes with PVP, with nylon-6, with 
1,3 dimethylurea and with glycine anhydride, as well as with other organic 
and inorganic compounds can be prepared by the method disclosed in detail 
below. 
Achieving suitable evaporation rates of anhydrous peroxide vapor from the 
source may be facilitated by elevated temperatures and/or reduced 
pressure. Thus, a heater for the peroxide source and/or a vacuum pump to 
evacuate the sterilization chamber are preferably a part of the 
sterilizer. Preferably, the source is covered with a layer of gas 
permeable material, such as TYVEK.TM. nonwoven polyethylene fabric, 
nonwoven polypropylene such as SPUNGUARD.TM., or similar material, which 
permits the peroxide vapor to pass but not the peroxide complexing 
material. Perforated aluminum or other suitable perforated material could 
also be used as a cover. 
FIG. 3A shows a device 80 that can be used to measure release of hydrogen 
peroxide from hydrogen peroxide complexes under various temperature 
conditions. In this device, an aluminum pan 90 is covered with a gas 
permeable layer 92, such as a layer of medical grade TYVEK.TM.. The pan 90 
is placed on top of a heating part 94 which is placed in a pyrex pan 96. A 
thermocouple thermometer 98 is placed on the outside of the pan 90 
approximately 1 cm from the bottom thereof. 
A preferred container 99 for holding the peroxide source is illustrated in 
FIG. 3B. The container 99 comprises a metal plate 100, e.g. an aluminum 
plate, with an optional attached heater used to heat the solid peroxide 
complex. A temperature monitor 101, such as a thermometer, can be placed 
on the plate 100 to monitor the temperature. The peroxide complex is 
placed directly on the plate 100. Alternatively, in order to provide even 
heating of all the peroxide complex, the peroxide complex can be placed 
between one or more aluminum screens 102, 104 placed on top of the plate 
100. The aluminum screens 102, 104 provide greater surface area and even 
heating of the complex when larger amounts of peroxide complex are being 
used. The peroxide complex, or the screen or screens 102, 104, are then 
covered with a gas permeable layer 106, such as a layer of medical grade 
TYVEK.TM. or SPUNGUARD.TM., so that the hydrogen peroxide released from 
the complex passes through the covering 106 before diffusing into the rest 
of the chamber. A perforated aluminum plate 108 is optionally placed on 
top of the TYVEK.TM. or SPUNGUARD.TM. layer 106 to provide pressure to 
keep the complex in contact with the heated plate 100 and to ensure even 
heating of the peroxide complex. 
The device just described provides even heating of the complex, which 
results in an increased amount of hydrogen peroxide vapor being released 
from the peroxide complex. 
FIG. 1 depicts a schematic of a hydrogen peroxide vapor sterilization 
apparatus of the present invention. Chamber 10 holds an article 12 which 
is to be sterilized and which, for convenience, is placed on shelf 14. 
Door 16 provides access to the interior of chamber 10. A non-aqueous 
source of hydrogen peroxide 18 is depicted on optional heater 20, which is 
controlled by temperature controller 22. The peroxide concentration can be 
monitored by optional monitor 24. If desired, chamber 10 can be evacuated 
using pump 26; however, sterilization can also be accomplished at 
atmospheric pressure. 
The container that holds the articles to be sterilized can be a 
conventional sterilization chamber, which is evacuated, or it can be a 
container (or a room) at atmospheric pressure. 
The time required to sterilize the articles depends on the nature, number 
and packaging of the articles and their placement in the chamber. 
Alternatively, it may be the chamber itself (or an entire room) that is 
being sterilized. In any case, optimum sterilization times can be 
determined empirically. 
The use of pressure pulsing to enhance the penetration and antimicrobial 
activity of sterilant gases, which is well known in the sterilization art, 
can also be applied to the non-aqueous hydrogen peroxide process. As 
described in additional detail hereinbelow, plasma can also be used to 
further enhance activity. 
At the conclusion of the sterilization process excess hydrogen peroxide can 
be removed from devices that have an affinity for peroxide by exchanging 
the air in contact with the devices. This can be accomplished by flowing 
warm air over the devices for an extended time or by evacuating the 
chamber. 
Articles that have previously been sterilized by exposure to hydrogen 
peroxide vapor may also be exposed to the plasma to remove residual 
hydrogen peroxide that may remain on the articles. Since the hydrogen 
peroxide is decomposed into non-toxic products during the plasma 
treatment, the sterilized articles may be used without the need for any 
additional steps. 
It may be desirable to isolate the peroxide source from the sterilizer 
after the peroxide vapor is released to avoid reabsorption of the vapor 
or, when a plasma is used, to avoid exposing the source to the plasma. 
Isolation is also advantageous when the complex used is not stable under 
vacuum. Isolation can be accomplished using valves or other isolating 
devices well known in the art. 
FIG. 2 depicts a schematic of a hydrogen peroxide plasma sterilization 
system of the present invention. Sterilization can be achieved with or 
without the use of plasma. The plasma can be used to enhance the 
sporicidal activity of the peroxide vapor, and/or to remove any residual 
hydrogen peroxide remaining on the sterilized articles. 
Sterilization is carried out in chamber 30, which includes a door or 
opening 32 through which articles to be sterilized can be introduced. The 
chamber 30 includes an outlet 34 to a vacuum pump 36, through which the 
chamber can be evacuated. The outlet 34 contains a valve 38 to isolate the 
chamber from the vacuum pump 36. The chamber 30 also includes an inlet 40 
attached to an enclosure 42 that contains the hydrogen peroxide complex. 
Inlet 40 contains a valve 44 that allows enclosure 42 to be isolated from 
the chamber. The sterilization system also contains an inlet 41 which 
connects the enclosure 42 and the vacuum pump 36, which contains a valve 
43. This system allows the simultaneous evacuation of both enclosure 42 
and chamber 30, or the independent evacuation of either enclosure 42 or 
chamber 30. Evacuation is controlled by the opening and closing of the 
valves 38, 44, and 43. As will be apparent to one having ordinary skill in 
the art, two pumps, one for each chamber, could also be employed in this 
system. 
The enclosure 42 contains an optional heater 49 attached to a temperature 
controller 46 to control the temperature of the hydrogen peroxide complex. 
The hydrogen peroxide complex concentration in the vapor state can be 
monitored by an optional peroxide monitor 48. The interior of the chamber 
contains a radio frequency (RF) electrode 50, to which is attached a 
matching network 52 and an RF power supply 54. A convenient form for the 
electrode is a perforated cylinder, surrounding the samples and open at 
both end. The general operation of the present process is as follows: 
1. The articles 56 to be sterilized are placed in the chamber 30. 
2. The chamber 30 may be at atmospheric pressure or, alternatively, may be 
evacuated to facilitate penetration of the hydrogen peroxide. Evacuation 
is accomplished by opening valve 38 and turning on vacuum pump 36. 
Alternatively, both the chamber 30 and the enclosure 42 may be evacuated 
by opening valves 38 and 44, and/or 43. 
3. The valves 38 and 43 are closed to isolate the vacuum pump 36 from the 
chamber 30 and enclosure 42, and the valve 44 is opened. Hydrogen peroxide 
vapor is delivered into chamber 30 from the hydrogen peroxide source, 
which may be heated to facilitate the release of the hydrogen peroxide 
vapor. Optionally, air or an inert gas may also be added. 
4. The articles 56 to be sterilized are either treated with peroxide vapor 
until sterilized or pretreated with peroxide vapor in the chamber 30 
before plasma with sufficient power to sterilize is generated. If 
necessary, chamber 30 may be evacuated at this time to facilitate 
generation of the plasma. The duration of the pre-plasma holding period 
depends on the type of package used, the nature and number of items to be 
sterilized, and the placement of the items in the chamber. Optimum times 
can be determined empirically. 
5. The articles 56 are subjected to a plasma by applying power from the RF 
power supply 54 to the RF electrode 50. The RF energy used to generate the 
plasma may be pulsed or continuous. The articles 56 remain in the plasma 
for a period to effect complete sterilization and/or to remove residual 
hydrogen peroxide. In certain embodiments, 5 to 30 minutes of plasma is 
used. However, optimum times can be determined empirically. 
When used in the present specification and claims, the term "plasma" is 
intended to include any portion of the gas or vapor that contains 
electrons, ions, free radicals, dissociated and/or excited atoms or 
molecules produced as a result of an applied electric field, including any 
accompanying radiation that might be produced. The applied field may cover 
a broad frequency range; however, a radio frequency or microwaves are 
commonly used. 
The non-aqueous hydrogen peroxide delivery system disclosed in the present 
invention can also be used with plasmas generated by the method disclosed 
in the previously mentioned U.S. Pat. No. 4,643,876. Alternatively, it may 
be used with plasmas described in U.S. Pat. No. 5,115,166 or 5,087,418, in 
which the article to be sterilized is located in a chamber that is 
separated from the plasma source. 
The device just described is particularly advantageous when using peroxide 
complexes that are not stable under vacuum. There are at least two 
possible methods that can be used to minimize the loss of hydrogen 
peroxide during the vacuum stage. First, the small chamber can be 
evacuated independently. Second, if a small enough chamber is used, there 
is no need to evacuate the small chamber at all. 
One such unstable non-aqueous peroxide complex is glycine 
anhydride-peroxide. This compound releases hydrogen peroxide vapor when 
placed under vacuum. FIG. 4 is a graph illustrating the release of 
hydrogen peroxide vapor from glycine anhydride-peroxide complex under 
vacuum. The procedure used to release the hydrogen peroxide from the 
glycine anhydride complex is as follows: (1) The main chamber 30 was 
evacuated with valves 43 and 44 closed. (2) The chamber containing the 
hydrogen peroxide complex 42 was evacuated with valves 38 and 44 closed 
and valve 43 open. (3) Valve 43 was closed and valve 44 was opened and 
hydrogen peroxide vapor was allowed to diffuse into chamber 30. 
As shown by the graph, hydrogen peroxide vapor is released from the complex 
as the pressure is reduced, even without additional heating. As 
illustrated in FIG. 4, release of peroxide vapor is significantly 
increased by heating the complex to a higher temperature. Thus, even 
unstable peroxide complexes are useful in the sterilization method of the 
present invention. 
The present invention provides at least four advantages over earlier 
hydrogen peroxide sterilization systems: 
1. The use of concentrated, potentially hazardous hydrogen peroxide 
solutions is circumvented. 
2. The need to reduce beforehand the relative humidity of areas to be 
sterilized in order to prevent condensation is eliminated. 
3. Water is substantially eliminated from the system, so that there is 
little competition between water and hydrogen peroxide for diffusion into 
long narrow lumens. 
4. The need to attach a special vessel to deliver sterilant gases into long 
narrow lumens can often be eliminated. 
That sterilization can be effected using hydrogen peroxide vapor in the 
substantial absence of moisture is one of the surprising discoveries of 
the present invention. The prior art teaches that the presence of water is 
required to achieve sterilization in chemical gas or vapor state 
sterilization processes. Advantageously, the present invention 
substantially eliminates water from the system, which results in faster, 
more efficient and effective sterilization. 
The sterilization efficacy of various non-aqueous hydrogen peroxide 
complexes was determined as described below in Example 1-4. 
EXAMPLE 1 
Efficacy data was obtained with hydrogen peroxide vapor released from 
substantially anhydrous urea peroxide complex using Bacillus subtilis var. 
(niger) spores in metal and TEFLON.TM. plastic lumens as the biological 
challenge. 
A. Test Procedures 
1. Equipment 
Four grams of crushed hydrogen peroxide urea adduct tablet (Fluka Chemical 
Corp, Ronkonkoma, N.Y.) were placed in an aluminum pan 90, as described in 
FIG. 3A. The top of the pan 90 was covered with medical grade TYVEK.TM. 92 
(a breathable spunbond polyethylene fabric) so that any hydrogen peroxide 
released from the complex would need to pass through the TYVEK.TM. 
covering before diffusing into the rest of the chamber. The aluminum pan 
90 was placed on a heating part 94 in a pyrex dish 96 located in the 
bottom of an aluminum sterilization chamber (see FIG. 1). The 
sterilization chamber, which had an approximate volume of 173 liters, also 
contained: 
A hydrogen peroxide monitor for measuring hydrogen peroxide concentration 
in the vapor phase. 
A temperature controller for controlling the temperature of the heating 
pad. 
An injection port through which liquid hydrogen peroxide could be injected 
into the chamber. 
A metal shelf on which a plastic tray containing lumen devices were placed 
for testing. 
Electrical resistance heaters on the exterior of the chamber walls, which 
maintained the chamber temperature at 45.degree. C. during the efficacy 
testings. 
2. Biological Challenge and Test 
To evaluate the efficacy of the non-aqueous peroxide delivery system, a 
biological challenge consisting of 1.04.times.10.sup.6 B. subtilis var. 
(niger) spores on a stainless steel scalpel blade was placed equally 
distant from each end of the stainless steel lumens of dimensions 3 mm 
ID.times.40 cm length, 3 mm ID.times.50 cm length, and 1 mm ID.times.50 cm 
length. These ID's and lengths are typical for metal lumens used in 
medical devices. The compartment in the middle of each lumen that 
contained the biological test piece had the dimensions 13 mm ID.times.7.6 
cm length. In the biological testing with metal lumens, a total of 9 
lumens were evaluated per test. These included 3 lumens from each of the 3 
different sets of ID's and lengths available. 
Similar tests were conducted with a biological challenge consisting of 
4.1.times.10.sup.5 B. subtilis var. (niger) spores on a paper strip (6 
mm.times.4 mm Whatman #1 chromatography paper) located equally distant 
from the ends of TEFLON.TM. lumens of dimensions 1 mm ID.times.1 meter 
length, 1 mm ID.times.2 meter length, 1 mm ID.times.3 meter length, and 1 
mm ID.times.4 meter length. The center compartment of these lumens that 
contained the biological test piece had the dimensions 15 mm ID.times.7.6 
cm length. In the biological testing with TEFLON.TM. lumens, a total of 12 
lumens were evaluated per test, 3 lumens from each of the 4 different 
lengths available. 
The lumens containing the biological test samples were placed in a plastic 
tray that was then placed on the shelf in the sterilization chamber. The 
chamber door was then closed and the chamber evacuated to 0.2 Torr 
pressure with a vacuum pump. The aluminum pan containing the hydrogen 
peroxide urea adduct was then heated to 80.degree. to 81.degree. C. for a 
period of 5 minutes, as measured by a thermocouple thermometer placed on 
the side wall of the aluminum pan approximately 1 cm from the bottom of 
the pan. During this time the concentration of hydrogen peroxide in the 
chamber increased to 6 mg/L as measured by the peroxide monitor. 
The biological test samples were exposed to the hydrogen peroxide vapor for 
periods of 5, 10, 15, 20, and 25 minutes. After exposure to the hydrogen 
peroxide vapor, the biological test samples were aseptically transferred 
into 15 mL of trypticase soy broth containing 277 units of catalase to 
neutralize any hydrogen peroxide residuals that may remain on the test 
samples. All samples were incubated for 7 days at 32.degree. C. and 
observed for growth. 
Comparative studies were also conducted in which a 50% aqueous solution of 
hydrogen peroxide was injected into the sterilization chamber and 
vaporized from a heated injector (a heated metal surface). The volume of 
hydrogen peroxide solution injected produced a vapor phase concentration 
of hydrogen peroxide of 6 mg/L. The test lumens and biological test 
samples used in these tests were identical to those used in the 
non-aqueous hydrogen peroxide tests. The handling of the biological test 
samples after exposure to the hydrogen peroxide was also identical. 
B. Test Results 
The results of these tests with stainless steel and TEFLON.TM. lumens, 
which are presented in Tables 3 and 4, respectively, illustrate the 
advantages of the non-aqueous peroxide delivery system with both metal and 
non-metal lumens. Total kill of the bacterial spores was achieved within 5 
minutes with the non-aqueous peroxide delivery system for the smallest ID 
and the longest lumens evaluated. At the same time, total kill was not 
achieved even after 25 minutes of diffusion time with the 50% hydrogen 
peroxide solution. 
TABLE 3 
______________________________________ 
Aqueous/Non-Aqueous Efficacy Comparison 
SS Blades in SS Lumens 
STERILITY RESULTS 
(POSITIVE/SAMPLES) 
SOURCE OF DIFFUSION 3 mm .times. 
3 mm .times. 
1 mm .times. 
PEROXIDE TIME (MIN) 
40 cm 50 cm 50 cm 
______________________________________ 
50% SOLUTION 
5 3/3 3/3 3/3 
10 0/3 2/3 3/3 
15 1/3 1/3 1/3 
20 0/3 0/3 1/3 
25 0/3 0/3 1/3 
UREA PEROXIDE 
5 0/3 0/3 0/3 
10 0/3 0/3 0/3 
15 0/3 0/3 0/3 
20 0/3 0/3 0/3 
25 0/3 0/3 0/3 
______________________________________ 
TABLE 4 
______________________________________ 
Aqueous/Non-Aqueous Efficacy Comparison 
6 mm .times. 4 mm Paper strip in TEFLON .TM. Lumens 
STERILITY RESULTS 
(POSITIVE/SAMPLES) 
SOURCE OF DIFFUSION 1 mm .times. 
1 mm .times. 
1 mm .times. 
1 mm .times. 
PEROXIDE TIME (MIN) 
1 m 2 m 3 m 4 m 
______________________________________ 
50% SOLUTION 
5 3/3 3/3 3/3 3/3 
10 3/3 3/3 3/3 3/3 
15 0/3 1/3 1/3 2/3 
20 0/3 0/3 1/3 1/3 
25 0/3 0/3 0/3 1/3 
UREA PEROXIDE 
5 0/3 0/3 0/3 0/3 
10 0/3 0/3 0/3 0/3 
15 0/3 0/3 0/3 0/3 
20 0/3 0/3 0/3 0/3 
25 0/3 0/3 0/3 0/3 
______________________________________ 
The fact that rapid sterilization can be accomplished in the absence of 
substantial amounts of water is surprising, in light of the fact that 
moisture has generally been present during chemical gas/vapor phase 
sterilization by various sterilants other than hydrogen peroxide. Since 
vapor phase hydrogen peroxide sterilization systems have used aqueous 
solutions of hydrogen peroxide, there has been moisture present in those 
systems as well. 
To test the sterilization efficacy of various other peroxide complexes, the 
following experiments were performed. 
EXAMPLES 2, 3 and 4 
The apparatus of Example 1 was used to test the efficacy of 
polyvinylpyrrolidone-hydrogen peroxide complex (Example 2), nylon 
6-hydrogen peroxide complex (Example 3), and 1,3 dimethylurea hydrogen 
peroxide complex (Example 4). These compounds were synthesized according 
to the method disclosed below in Examples 12 and 13. Test parameters were 
as follows: 
______________________________________ 
Example 
2 3 4 
______________________________________ 
Chamber Temp. 45.degree. C. 
45.degree. C. 
45.degree. C. 
Initial Pressure 0.2 Torr 1.0 Torr 1.0 Torr 
Wt. % of peroxide 
17% 10.5% 26.6% 
Peroxide concentration 
6 mg/L 6 mg/L 6 mg/L 
Wt. of complex used 
8 g 18 g 6 g 
per cycle 
Temp to release peroxide 
110.degree. C. 
110.degree. C. 
80.degree. C. 
______________________________________ 
In each case, spore supports were 6 mm.times.4 mm paper substrates in 
plastic lumens and stainless steel blades in stainless steel lumens. The 
results of this efficacy testing appear below in Table 5. 
TABLE 5 
______________________________________ 
Efficacy of Complexes with PVP, 
nylon 6, and 1,3-dimethylurea 
STERILITY RESULTS 
(POSITIVE/SAMPLES) 
TYPE OF SIZE OF With 5 Minutes Exposure 
LUMEN LUMENS Example 2 Example 3 
Example 4 
______________________________________ 
TEFLON .TM. 
1 mm .times. 1 m 
0/3 0/3 0/3 
1 mm .times. 2 m 
0/3 0/3 0/3 
1 mm .times. 3 m 
0/3 0/3 0/3 
1 mm .times. 4 m 
0/3 0/3 0/3 
STAINLESS 
3 mm .times. 40 cm 
0/3 0/3 0/3 
STEEL 3 mm .times. 50 cm 
0/3 0/3 0/3 
1 mm .times. 50 cm 
0/3 0/3 0/3 
______________________________________ 
The results appearing in Table 5 show that each of the tested hydrogen 
peroxide complexes generate peroxide vapor which provides efficient 
sterilization after only five minutes exposure. 
The temperature required to release the hydrogen peroxide vapor from the 
solid complex which is shown above is the temperature measured by a 
thermocouple thermometer located on the outside of the aluminum pan 
approximately 1 cm from the bottom of the pan. Further testing using a 
thermometer, such as a fluoroptic thermometer, placed on the inside bottom 
of the pan indicated that the temperature at the bottom of the pan was 
approximately 30.degree.-35.degree. C. higher, as described in Example 5 
below. Thus, in the previous example, the temperature at the bottom of the 
pan was approximately 110.degree.-115.degree. C. when the thermocouple 
thermometer read 80.degree. C., and the temperature at the bottom of the 
pan was approximately 140.degree.-145.degree. C. when the thermocouple 
thermometer read 110.degree. C. 
EXAMPLE 5 
To determine the temperature at the bottom of the aluminum pan used to 
contain the solid peroxide complex, a fluoroptic thermometer was taped to 
the inside bottom of the aluminum pan. An Omega.TM. thermocouple 
thermometer was placed on the outside of the aluminum pan approximately 1 
cm from the bottom of the pan. Three different readings of the 
thermometers were taken. Each time the pan was heated to the desired 
temperature indicated by the thermometer placed on the side of the pan, 
allowed to cool, and then re-heated to the desired temperature. The 
recorded temperatures are listed below: 
______________________________________ 
Temp. at Temp. at bottom of pan (.degree.C.) 
side of pan 1st 2nd 3rd avg 
______________________________________ 
80.degree. C. 
110.9 110.6 110.6 
110.7 
100.degree. C. 
131.5 132.6 132.0 
132.0 
______________________________________ 
The results show that the temperature at the bottom of the aluminum pan was 
approximately 30.degree.-35.degree. C. higher than the temperature 
indicated by the thermocouple thermometer located at the side of the pan. 
Further testing was performed to compare the efficacy data obtained using 
an aqueous and non-aqueous source of peroxide in an open (non-lumen) 
system. The experiments are described in detail below. 
EXAMPLE 6 
The apparatus of Example 1 was used with a biological challenge that 
consisted of 6.8.times.10.sup.5 B. subtilis var (niger) spores on a 6 
mm.times.4 mm strip of Whatman #1 chromatography paper packaged in a 
TYVEK.TM./MYLAR.TM. envelope. (TYVEK.TM. is a gas permeable fabric made of 
polyethylene. MYLAR.TM. is a non-gas permeable polyester material). 
Packaged biological challenge strips were placed in the front, middle and 
back of a polyphenylene oxide tray that contained a flexible fiberoptic 
sigmoidoscope. The tray was placed in a polyphenylene oxide container that 
had one port in the top and two ports in the bottom to allow for 
diffusion. The four-inch diameter ports were covered with a breathable 
polypropylene packaging material (SPUNGUARD.TM. Heavy Duty Sterilization 
Wrap, Kimberly-Clark, Dallas, Tex.) to maintain the sterility of the 
contents of the container after sterilization. The container was placed in 
the apparatus of Example 1 and the pressure in the chamber was reduced to 
0.2 Torr. The aluminum pan containing 2 grams of hydrogen peroxide urea 
adduct (Fluka Chemical Corp.) was then heated to 80.degree. to 81.degree. 
C., as measured by a thermocouple thermometer placed on the outside of the 
aluminum pan approximately 1 cm from the bottom of the aluminum pan, for 5 
minutes to provide 3 mg/L of hydrogen peroxide vapor in the chamber. The 
biological test samples were exposed to the hydrogen peroxide vapor for 
periods of 5 and 10 minutes. After exposure the test samples were handled 
in the same way as were those in Example 1. 
Comparative studies were also conducted in which a 50% aqueous solution of 
hydrogen peroxide was injected into the sterilization chamber and 
vaporized from a heated injector. The volume of hydrogen peroxide solution 
injected produced a vapor phase concentration of 3 mg/L. The test 
configuration, the composition of the biological test samples, and the 
handling of the biological test samples after exposure were all identical 
to those used in the non-aqueous hydrogen peroxide tests. The results of 
these tests are presented in Table 6. 
TABLE 6 
______________________________________ 
Aqueous/Non-Aqueous Efficacy 
Comparison in Open System 
(Non-Lumen Test) 
Diffusion 
Sterility 
Source of Time Results 
Peroxide (min) (positive/samples) 
______________________________________ 
50% solution 5 3/3 
10 3/3 
Urea Peroxide 5 1/3 
10 0/3 
______________________________________ 
The results of these tests demonstrate the greater efficacy of the 
non-aqueous when compared with the aqueous hydrogen peroxide process in an 
"open" system in which the biological sample was not placed in a lumen. 
Again, it was surprisingly discovered that a non-aqueous system provided 
superior sterilization even when diffusion of hydrogen peroxide into a 
long and narrow lumen is not required. This suggests that the mode of 
action of hydrogen peroxide is not the same for systems with and without 
water. 
Further testing was performed to determine the efficacy a non-aqueous 
peroxide vapor at normal, not reduced, pressure. This testing is detailed 
below. 
EXAMPLE 7 
Efficacy tests were conducted with the hydrogen peroxide vapor released 
from the urea peroxide complex in an open system at atmospheric pressure. 
In this test the biological challenge of 1.04.times.10.sup.6 B. subtilis 
var. (niger) spores on the stainless steel surgical blades were packaged 
in a TYVEK.TM./MYLAR.TM. envelope. Packaged biological challenge blades 
were placed on the front, middle, and back of a polyphenylene oxide tray. 
The tray was placed in the apparatus of Example 1 and the chamber door was 
closed. The aluminum pan containing 4.0 gm of urea peroxide (Fluka 
Chemical Corp.) was heated to 80.degree. to 81.degree. C., as measured by 
a thermocouple thermometer placed on the side of the aluminum pan 
approximately 1 cm from the bottom of the pan, for the duration of the 
test. The biological test samples were exposed to the hydrogen peroxide 
vapor for periods of 5, 10, 20 and 30 minutes. After exposure the test 
samples were handled the same way as those in Example 1. The results of 
these tests are presented in Table 7 and demonstrate the efficacy of the 
non-aqueous peroxide process in an open system at atmospheric pressure. 
TABLE 7 
______________________________________ 
Efficacy of non-aqueous peroxide process in open system 
at atmospheric pressure 
Diffusion 
Sterility 
Source of Time Results 
Peroxide (minutes) 
(positive/samples) 
______________________________________ 
Urea 5 3/3 
Peroxide 10 1/3 
20 0/3 
30 0/3 
______________________________________ 
Further tests were conducted to determine the approximate amount of 
peroxide released from the hydrogen peroxide urea complex at various 
temperatures. This testing is described in Example 8. 
EXAMPLE 8 
Urea peroxide powder, obtained from crushing the commercially available 
tablets (Fluka Chemical Corp.), was placed between two aluminum screens in 
an apparatus according to FIG. 3B having dimensions 12.7 cm .times.12.7 
cm. The aluminum plate was then heated and the temperature was monitored 
using a thermometer located near a corner of the aluminum plate. Table 8 
lists the approximate percent of peroxide released at various temperatures 
after heating for five minutes. The data show that approximately 100% of 
the peroxide is released from the complex at a temperature of 140.degree. 
C. Lesser percentages of peroxide are released at lower temperatures. 
TABLE 8 
______________________________________ 
Release of non-aqueous peroxide at various temperatures 
Heating Temperature 
% Peroxide Released 
______________________________________ 
80.degree. C. .about.25% 
100.degree. C. .about.65% 
120.degree. C. .about.80% 
130.degree. C. .about.90% 
140.degree. C. .about.100% 
______________________________________ 
Peroxide complexes having the ability to release hydrogen peroxide vapor at 
room temperature and atmospheric pressure, such as the urea peroxide 
complex, allows them to be effective for use in various sterilization 
applications. Not only can they be used in the sterilization apparatus of 
the present invention described above, the compounds of the present 
invention can also be used as part of self-sterilizing packaging 
materials, or applied onto supports such as gauze, sponge, cotton, and the 
like. The compounds allow for sterilization of sealed packages at room 
temperature or at elevated temperatures, and are particularly useful for 
the sterilization of packaged medical or surgical products. 
Particular uses of the compounds of the present invention are described in 
the examples which follow. The peroxide complex used in the following 
examples was urea peroxide in the form of a tablet (Fluka Chemical Corp.) 
or in the form of a powder obtained by crushing the tablets. 
EXAMPLE 9 
A self-sterilizing pouch was assembled as follows: A surgical scalpel 
having 3.8.times.10.sup.5 B. subtilis var. niger spores on its surface was 
placed in a sterile petri dish. The dish was placed in a larger petri 
dish, together with 1 gm urea peroxide complex in either tablet or powder 
form. The larger petri dish was then inserted into a pouch formed of 
TYVEK.TM./MYLAR.TM. (gas permeable, Table 9), MYLAR.TM./MYLAR.TM. (non-gas 
permeable, Table 10) or Paper/MYLAR.TM. (gas permeable, Table 10). The 
pouch was then sealed. 
Each pouch was exposed to various temperatures for various time periods, as 
shown in Tables 9 and 10 below. The biological test samples were evaluated 
for sterilization as described in Example 1. The results are included in 
Tables 9 and 10, with a "+" sign indicating bacterial growth. 
TABLE 9 
______________________________________ 
Self-Sterilizing Pouches 
With Breathable Barrier (TYVEK .TM./MYLAR .TM.) 
Temperature 
Peroxide Type 
1 hr. 2 hr. 3 hr. 4 hr. 
______________________________________ 
23.degree. C. 
powder + - - - 
table + + - - 
40.degree. C. 
powder - - - - 
tablet - - - - 
60.degree. C. 
powder - - - - 
tablet - - - - 
______________________________________ 
Table 10 lists the efficacy data for self-sterilizing pouches with 
(Paper/MYLAR.TM.) and without (MYLAR.TM./MYLAR.TM.) a breathable barrier. 
The pouches were assembled as described above, however the peroxide vapor 
source was urea peroxide in powder form only. 
TABLE 10 
______________________________________ 
Self-Sterilizing pouches With & Without Breathable Barrier 
Temperature Packaging Type 2 hr. 4 hr. 
______________________________________ 
23.degree. C. 
MYLAR/MYLAR - - 
Paper/MYLAR + - 
40.degree. C. 
MYLAR/MYLAR - - 
Paper/MYLAR - - 
60.degree. C. 
MYLAR/MYLAR - - 
Paper/MYLAR - - 
______________________________________ 
Results from this testing show that the urea peroxide complex of the 
present invention included in a pouch with and without a breathable 
barrier provides effective sterilization to an article inside the pouch in 
the absence of moisture at room temperature and atmospheric pressure after 
only 2 to 3 hours. At higher temperatures, sterilization is effected after 
only one hour. 
To determine the efficacy of the sterilization system of the present 
invention in a closed container, the following experiment was performed. 
EXAMPLE 10 
A self-sterilizing container was assembled as follows: A stainless steel 
support having either 3.8.times.10.sup.5 B. subtilis var. niger spores on 
its surface (Table 11) or having 9.2.times.10.sup.5 B. subtilis var. niger 
spores on its surface (Table 12), was placed inside a small polyethylene 
(PE) vial having 20 holes (3/16" in size) in its surface. The vial was 
placed in a larger PE vial, which was covered with either an air tight 
cap, or a gas permeable layer of SPUNGUARD.RTM. (CSR Wrap). Also included 
in the larger vial was a second PE vial, also having 20 holes (3/16" in 
size) in its surface. This vial contained 1 gm urea peroxide in either 
powder or tablet form, and was sealed in either a SPUNGUARD.TM. (CSR wrap) 
or TYVEK.TM. pouch. 
Each container was exposed to various temperatures for various time 
periods, as shown in Tables 11 and 12 below. The biological test samples 
were evaluated for sterilization as described in Example 1. The results 
are included in Tables 11 and 12, with a "+" sign indicating bacterial 
growth. 
TABLE 11 
______________________________________ 
Self-Sterilizing Containers Without Breathable Window 
Temperature Packaging Type 2 hr. 6 hr. 
______________________________________ 
23.degree. C. 
Unpackaged tablet 
+ - 
C/C* packaged tablet 
+ - 
C/C packaged powder 
+ - 
40.degree. C. 
Unpackaged tablet 
- - 
C/C packaged tablet 
- - 
C/C packaged powder 
- - 
60.degree. C. 
Unpackaged tablet 
- - 
C/C packaged tablet 
- - 
C/C packaged powder 
- - 
______________________________________ 
*pouch formed from CSR wrap 
TABLE 12 
______________________________________ 
Self-Sterilizing Containers With Breathable CSR Window 
0.5 1.0 1.5 2.0 3.0 4.0 
Temperature 
Packaging Type 
hr. hr. hr. hr. hr. hr. 
______________________________________ 
23.degree. C. 
Unpackaged tablet + + + - - 
Unpackaged powder + + + - - 
T/T* packaged tablet 
+ + + + - 
T/T packaged powder + + + - - 
C/C** packaged tablet 
+ + + - - 
C/C packaged powder + + + - - 
40.degree. C. 
Unpackaged tablet 
- - - - 
Unpackaged powder 
- - - - 
T/T packaged tablet 
+ - - - 
T/T packaged powder 
- - - - 
C/C packaged tablet 
- - - - 
C/C packaged powder 
- - - - 
60.degree. C. 
Unpackaged tablet 
- - - - 
Unpackaged powder 
- - - - 
T/T packaged tablet 
- - - - 
T/T packaged powder 
- - - - 
C/C packaged tablet 
- - - - 
C/C packaged powder 
- - - - 
______________________________________ 
*- pouch formed from TYVEK 
** pouch formed from CSR wrap 
Results from this testing show that the non-aqueous urea peroxide complex 
included in a container with and without a breathable barrier provides 
effective sterilization at room temperature after only 3-4 hours. At 
higher temperatures, sterilization is effected after as little as one half 
hour. 
The non-aqueous peroxide complexes which release peroxide vapor have been 
found to be useful in the sterilization of articles at room temperature, 
and more effectively, at higher temperatures. These complexes can be 
placed in a pouch, container, chamber, room or any area capable of being 
sealed, where they release peroxide vapor which effectively sterilizes the 
articles. The complexes can be heated to facilitate the release of vapor, 
and to provide sterilization in less time than that required for room 
temperature sterilization. The compounds of the present invention are 
therefore useful in a variety of applications where sterilization is 
desired. Simply by placing the complex in a sealed area containing an 
article or articles to be sterilized, sterilization can be achieved. By 
contrast with prior art methods, there is no need for contact with 
moisture to provide activation of the hydrogen peroxide. 
To confirm that sterilization can be effected using non-aqueous peroxide 
complexes in less time at lower pressures, the following experiment was 
performed. 
EXAMPLE 11 
A self-sterilizing container was assembled as follows: A stainless steel 
support having 9.2.times.10.sup.5 B. subtilis var. niger spores on its 
surface was placed inside a small PE vial having 20 holes (3/16" in size) 
in its surface. The vial was placed in a larger PE vial, which was covered 
with a gas permeable layer of CSR wrap (SPUNGUARD.TM.). Also included in 
the larger vial was a second PE vial, also having 20 holes (3/16" in size) 
in its surface. This vial contained 1 gm urea peroxide in either powder or 
tablet form. The vial was then sealed in a CSR wrap or TYVEK.TM. pouch. 
The large vials were placed in either a 4.5 L sterilization chamber or a 
173 L sterilization chamber. Each container was exposed to 100 torr 
pressure and 23.degree. C. temperature for 2 hours, as shown in Table 13. 
The biological test samples were evaluated for sterilization as described 
in Example 1. The results are included in Table 13. 
TABLE 13 
______________________________________ 
Self-Sterilizing Contained With Breathable Window 
In Reduced Pressure Conditions 
Temperature 
Packaging Type 4.5 L chamber 
173 L chamber 
______________________________________ 
23.degree. C. 
Unpackaged powder 
- - 
T/T packaged powder 
- - 
C/C packaged powder 
- - 
______________________________________ 
These results show that non-aqueous urea peroxide complex included in a 
container with a breathable barrier provides effective sterilization at 
100 torr and room temperature after only 2 hours. These results, when 
compared with the results in Table 12, demonstrate that the peroxide 
complexes of the present invention provide sterilization at reduced 
pressures in less time than that required to effect sterilization at 
atmospheric pressure. 
Thus, the hydrogen peroxide complexes of the present invention can provide 
effective sterilization in significantly shorter periods of time. In 
addition, as discussed above, plasma can also be used to enhance the 
sterilization activity of the hydrogen peroxide vapor. The articles to be 
sterilized are subjected to a plasma after exposure to the peroxide vapor, 
and remain in the plasma for a period of time sufficient to effect 
complete sterilization. 
Articles that have been sterilized by exposure to hydrogen peroxide vapor 
can be exposed to a plasma to remove any residual hydrogen peroxide 
remaining on the articles. Because the residual hydrogen peroxide is 
decomposed into non-toxic products during the plasma treatment, the 
sterilized articles are ready for use following treatment, without the 
need for any additional steps. 
Non-aqueous peroxide complexes are useful in a variety of applications, 
including as a component of self-sterilizing packaging. In addition, the 
complexes are suitable for use in various methods for vapor sterilization 
of articles, such as the method disclosed in U.S. Pat. No. 4,943,414. This 
patent discloses a process in which a vessel containing a small amount of 
a vaporizable liquid sterilant solution is attached to a lumen, and the 
sterilant vaporizes and flows directly into the lumen of the article as 
the pressure is reduced during the sterilization cycle. The method 
disclosed in the patent can be modified to allow for use of a non-aqueous 
peroxide compound. The compound is placed in a vessel and connected to the 
lumen of the article to be sterilized. The article is then placed within a 
container and the container evacuated. The lumen of the article and the 
exterior of the article are contacted by the hydrogen peroxide vapor 
released from the non-aqueous compound. A plasma can optionally be 
generated and used to enhance sterilization and/or to remove any residual 
hydrogen peroxide form the article. 
Use of non-aqueous peroxide complexes in the system just described 
overcomes the disadvantage that the water in the aqueous solution is 
vaporized faster and precedes the hydrogen peroxide vapor into the lumen. 
Thus, more effective sterilization is achieved and less time is required 
to effect sterilization. Hydrogen peroxide complexes such as glycine 
anhydride are especially advantageous since they release a significant 
amount of hydrogen peroxide at reduced pressure without the need for 
additional heating of the complex. 
Synthesis of Non-Aqueous Hydrogen Peroxide Complexes 
The present invention further provides a process for preparing non-aqueous 
hydrogen peroxide complexes that are useful as the source in a hydrogen 
peroxide vapor sterilizer, or as a component of self-sterilizing 
packaging, as was described above. Of course, the hydrogen peroxide 
complexes can be used for other applications, such as for bleaching 
agents, contact lens solutions, catalysts, and other applications which 
will be well known by those having ordinary skill in the art. 
The general procedure for preparing the hydrogen peroxide complexes of this 
invention is as follows: 
(1) Place the reactant material in the chamber. 
The material to be reacted with the hydrogen peroxide can be a solid in 
various forms, (e.g., powder, crystal, film etc., preferably having high 
surface area to increase the reaction rate). The reactant material can 
also be present as a solution in water or another solvent, if sufficient 
time is allowed to evaporate the solvent after the pressure is reduced in 
the chamber. The material may also be a liquid whose boiling point is 
higher than that of hydrogen peroxide (150.degree. C.). Since reaction 
rates are faster at elevated temperature, the chamber is preferably heated 
whether before or after the reactant composition is introduced. However, 
the temperature should not be so high that the reactant boils or 
vaporizes. 
The reactant composition may be contained in any container that provides 
access to the peroxide vapor. If it is in the form of a powder or other 
form that may be blown about when the chamber is evacuated, then the 
reactant may be retained in a permeable container, which allows hydrogen 
peroxide to diffuse into the container. 
(2) Evacuate the chamber. 
Preferably, the chamber is evacuated to a pressure that is below the vapor 
pressure of the hydrogen peroxide (which depends on its concentration and 
temperature), in order to assure that all of the peroxide is in the vapor 
phase. The vapor pressure increases with increasing temperature and 
decreases with increasing peroxide concentration. For most of the 
experiments, the chamber was evacuated to about 0.2 Torr and the 
temperature was ambient or above. 
(3) Generate hydrogen peroxide vapor. 
The hydrogen peroxide vapor can be generated from a hydrogen peroxide 
solution or from a substantially anhydrous hydrogen peroxide complex. The 
latter yields dry hydrogen peroxide in the vapor state, which is an 
advantage if either the material to be reacted with the vapor or the 
complex to be formed is hygroscopic. Another advantage of generating the 
hydrogen peroxide vapor from a substantially water-free complex is that 
the percent of hydrogen peroxide in the complex being formed is higher 
than if the vapor is generated from an aqueous solution of H.sub.2 
O.sub.2. This is probably due to the competition between water molecules 
and H.sub.2 O.sub.2 molecules for bonding sites on the complex when an 
aqueous solution is used to generate the H.sub.2 O.sub.2 vapor. 
The peroxide vapor can be generated within the same chamber that houses the 
reactant material or in another chamber separated from it by a vacuum 
valve. 
(4) React the reactant material with hydrogen peroxide. 
The time required for the reaction depends, of course, on the reaction rate 
of the reactant with hydrogen peroxide. It can be empirically determined 
by monitoring the pressure, which decreases during the binding of peroxide 
to the reactant material. Typically, the reaction time is about 5-30 
minutes. The concentration of vaporized hydrogen peroxide and the weight 
of the starting material determine the weight percentage of peroxide in 
the final reaction product. As the weight ratio of reactant to hydrogen 
peroxide increases, the weight percentage of hydrogen peroxide in the 
complex decreases. The reaction can be repeated multiple times to increase 
the concentration of hydrogen peroxide in the complex. 
(5) Evacuate the chamber again. 
At the end of the reaction period, the chamber is further evacuated to 
about 2 Torr to remove any unreacted hydrogen peroxide. 
(6) Vent the chamber and retrieve the hydrogen peroxide complex. 
The mechanism by which the hydrogen peroxide forms a complex with the 
reactant material is not completely understood. The formation of the 
complex is believed to involve hydrogen bond formation between the 
hydrogen peroxide and electron-rich functional groups containing oxygen 
and/or nitrogen on the reactant material. It is not known if this is the 
only mode of binding; however, materials with a wide range of functional 
groups have been found to form complexes with hydrogen peroxide. 
The advantages of the vapor phase reaction over earlier methods of hydrogen 
peroxide complex formation include: 
1. The ratio of hydrogen peroxide to reactant material can be accurately 
controlled by varying the amount of hydrogen peroxide present in the vapor 
state or the amount of reactant material exposed to the vapor. 
2. The need to remove solvent from the reaction product is eliminated. 
3. Peroxide complexes can be formed that are liquid or solids, such as 
powders, crystals, films, etc. 
4. Peroxide complexes of hygroscopic materials can be prepared. 
The synthesis of the non-aqueous peroxide complexes according to the 
present invention is further described in the following examples. Many of 
these compounds have utility as catalysts, in addition to having the 
utilities described in greater detail herein, as will be readily 
appreciated by those having ordinary skill in the art. The examples 
represent embodiments of the compositions and processes of the invention, 
but they are not in any way intended to limit the scope of the invention, 
EXAMPLE 12 
A hydrogen peroxide complex of glycine anhydride was prepared as follows: A 
1.0 gram sample of glycine anhydride (Aldrich Chemical Co., Milwaukee, 
Wis.) was placed in an aluminum tray in a 173 liter chamber maintained at 
a temperature of 45.degree. C. The top of the aluminum tray was covered 
with TYVEK.TM. nonwoven fabric, which prevented the glycine anhydride from 
coming out of the tray when the pressure in the chamber was reduced but 
was breathable and did not absorb hydrogen peroxide. The chamber door was 
closed and the pressure in the chamber was reduced to 0.2 Torr by 
evacuating the chamber with a vacuum pump. A hydrogen peroxide 
concentration of 10 mg/liter was created by evaporation of an appropriate 
volume of a 70% aqueous solution of hydrogen peroxide (FMC Corp., 
Philadelphia, Pa.) into the chamber. The hydrogen peroxide vapor was 
maintained in contact with the glycine anhydride for 20 minutes. At the 
end of the reaction period, the chamber pressure was reduced to 2 Torr and 
then returned to atmospheric pressure. The reaction product was removed 
from the chamber and analyzed for weight percent hydrogen peroxide by the 
following iodometric titration reactions. 
EQU H.sub.2 O.sub.2 +2KI+H.sub.2 SO.sub.4 .fwdarw.I.sub.2 +K.sub.2 SO.sub.4 
+2H.sub.2 O 
EQU I.sub.2 +2Na.sub.2 S.sub.2 O.sub.3 .fwdarw.Na.sub.2 S.sub.4 O.sub.6 +2Nal 
A starch indicator was used in the iodine-sodium thiosulfate titration 
reaction to enhance the color change at the end point. The percentage by 
weight of hydrogen peroxide was calculated by the following equation: 
EQU wt % H.sub.2 O.sub.2 =[(ml of Na.sub.2 S.sub.2 O.sub.3)*(normality of 
Na.sub.2 S.sub.2 O.sub.3)*1.7]/(sample weight in grams) 
The weight percentage of hydrogen peroxide in the glycine anhydride complex 
was found to be 24.3%. 
EXAMPLE 13 
The hydrogen peroxide complexes of a wide variety of organic and inorganic 
complexes were prepared using the procedure of Example 12. In each case, 
the reaction conditions were the same as those in Example 12, except 1.0 
gram of each one of the compounds presented in Table 14 was used in place 
of glycine anhydride. 
TABLE 14 
__________________________________________________________________________ 
COMPOUNDS EVALUATED AND WEIGHT PERCENT HYDROGEN PEROXIDE 
PRESENT IN COMPLEXES FORMED BY VAPOR PHASE SYNTHESIS PROCESS 
Wt % After 
Peroxide 
Chemical Name 
Chemical Structure 
Treatment 
Category 
__________________________________________________________________________ 
Poly(vinyl alcohol) 
[CH.sub.2 CH(OH)].sub.n 
18.9% Alcohol 
Poly(vinyl methyl ether) 
[CH.sub.2 CH(OCH.sub.3)].sub.n 
22.0% Ether 
Poly(vinyl methyl Ketone) 
[CH.sub.2 CH(COCH.sub.3)].sub.n 
13.9% Ketone 
Poly(acrylic acid) 
[CH.sub.2 CH(COOH)].sub.n 
5.1% Acid 
Glycine H.sub.2 C(NH.sub.2)(COOH) 
20.7% Amino Acid 
L-Histidine 
##STR1## 14.1% Amino Acid 
Poly(vinyl acetate) 
[CH.sub.2 CH(OCOCH.sub.3)].sub.n 
9.1% Ester 
Cellulose acetate 10.9% Ester 
Sodium alginate 27.7% Organic Salt 
Cellulose sulfate, sodium salt 18.2% Organic Salt 
Poly(4-Vinylpyridine) 
[CH.sub.2 CH(.rho.-C.sub.5 H.sub.4 N)].sub.n 
21.8% Aromatic amine 
Histamine 
##STR2## 13.2% Amine 
Propionamide (C.sub.2 H.sub.5)CONH.sub.2 
31.8% Amide 
Urea (H.sub.2 N).sub.2 CO 
17.9% Urea 
1,3-dimethylurea 
(H.sub.3 C)HNCONH(CH.sub.3) 
31.7% Urea 
Biuret (H.sub.2 N)CO(NH)CO(NH.sub.2) 
13.7% Biuret 
Polyacrylamide 
[CH.sub.2 CH(CONH.sub.2)].sub.n 
30.1% Polyamide 
Polyvinylpyrrolidone 
##STR3## 29.9% Polyamide 
Nylon 6 [NH(CH.sub.2).sub.5 CO].sub.n 
17.1% Polyamide 
Nylon 6,6 film 
[NH(CH.sub.2).sub.6 NHCO(CH.sub.2).sub.4 CO].sub.n 
16.6% Polyamide 
Polyetherpolyurethane 
[RHNCOOR'].sub.n 9.5% Polyurethane 
Sodium carbonate 
Na.sub.2 CO.sub.3 14.3% Inorganic 
Potassium carbonate 
K.sub.2 CO.sub.3 33.9% Inorganic 
Rubidium carbonate 
Rb.sub.2 CO.sub.3 37.0% Inorganic 
Calcium hydroxide 
Ca(OH).sub.2 23.4% Inorganic 
Sodium bicarbonate 
NaHCO.sub.3 10.7% Inorganic 
Tetrasodium pyrophosphate 
Na.sub.4 P.sub.2 O.sub.7 
18.9% Inorganic 
__________________________________________________________________________ 
The organic complexes formed cover the following range of functional groups 
that are capable of forming hydrogen bonds with hydrogen peroxide: 
alcohols, ethers, ketones, acids, amino acids, esters, organic salts, 
amines, amides, polyamides, polyurethanes, ureas, and biuret. The 
inorganic complexes include carbonates with sodium, potassium, and 
rubidium cations, as well as sodium bicarbonate. In addition, the hydrogen 
peroxide complexes of calcium hydroxide and tetrasodium pyrophosphate were 
also prepared. The starting materials were finely divided powers or 
slightly larger crystalline materials, except for nylon 6,6, which was 
processed as a film with a thickness of 0.12 mm, and polyvinyl methyl 
ether, which was a 50% by weight aqueous solution. 
The hydrogen peroxide complexes obtained with these materials under the 
test conditions were solids, except for polyvinylpyrrolidone, histamine, 
poly(vinyl methyl ether), poly(vinyl methyl ketone),propionamide, and 
1,3-dimethylurea. The 1,3-dimethylurea and propionamide hydrogen peroxide 
complexes were free flowing liquids that were easily handled in the vapor 
phase synthesis process, since no solvent needed to be removed to obtain 
the final product. The histamine, polyvinylpyrrolidone, poly(vinyl methyl 
ether), and poly(vinyl methyl ketone) complexes were gummy materials that 
were not as easy to handle. 
Example 14 and 15 describe additional studies with polyvinylpyrrolidone 
under different process conditions to obtain the peroxide complex as a 
free flowing solid product. 
EXAMPLE 14 
Hydrogen peroxide complexes with polyvinylpyrrolidone were prepared in 
which the percent hydrogen peroxide in the polyvinylpyrrolidone complex 
was varied by changing the ratio of the weight of polyvinylpyrrolidone to 
the concentration of hydrogen peroxide in the vapor state. The conditions 
in these tests were identical to those in Example 12, except the weight of 
polyvinylpyrrolidone was increased from 1.0 gram to 3.0 grams to 5.0 
grams. In all tests, the concentration of hydrogen peroxide was held 
constant at 10.0 mg/liter of chamber volume. The results of these tests 
are presented in Table 15. 
EXAMPLE 15 
A hydrogen peroxide complex of PVP was prepared in which the hydrogen 
peroxide was delivered from a complex of hydrogen peroxide with urea. When 
hydrogen peroxide is delivered in this manner, it is substantially water 
free. In this test, 5 grams of PVP was placed in the reaction chamber and 
10 mg H.sub.2 O.sub.2 /liter of chamber volume was delivered into the 
reaction chamber by heating about 7 grams of a 35% complex of H.sub.2 
O.sub.2 with urea to a temperature of about 110.degree. C. for 
approximately 5 minutes. The rest of the conditions in this test were the 
same as those in Example 12. The percentage hydrogen peroxide in the PVP 
complex and the physical state of the complex are presented in Table 15. 
TABLE 15 
______________________________________ 
EFFECT OF RATIO OF POLYVINYLPYRROLIDONE TO 
HYDROGEN PEROXIDE IN THE VAPOR STATE ON % HYDROGEN 
PEROXIDE IN COMPLEX AND PHYSICAL STATE OF PRODUCT 
Weight 
Wt % H.sub.2 O.sub.2 
Physical State 
PVP (g) 
in Complex of Product 
______________________________________ 
Ex. 14 1 29.9 Soft gummy product 
3 23.5 Hard gummy product 
5 17.7 Free flowing solid 
Ex. 15 5 19.7 Free flowing solid 
______________________________________ 
The results of these tests demonstrate that a free flowing solid can be 
obtained with the PVP hydrogen peroxide complex by controlling the ratio 
of PVP to hydrogen peroxide in the vapor state and, alternatively, by 
using a substantially water-free hydrogen peroxide vapor source. 
INORGANIC HYDROGEN PEROXIDE COMPLEXES 
Inorganic hydrogen peroxide complexes are also suitable for use as 
sterilants as described in detail hereinabove for organic hydrogen 
peroxide complexes. Peroxide vapor can be released from these inorganic 
complexes at atmospheric pressure and room temperature. However, as 
described in greater detail below, substantial amounts of hydrogen 
peroxide vapor can be released from inorganic peroxide complexes upon 
rapid heating to a particular release temperature under reduced pressure. 
In order to successfully release hydrogen peroxide from inorganic 
peroxide, the heating rate of the inorganic peroxide complexes is 
preferably at least 5.degree. C./min; more preferably it is at least 
10.degree. C. per minute; still more preferably at least 50.degree. 
C./min.; and most preferably, it is at least 1000.degree. C. per minute. 
A representative listing of these inorganic peroxide complexes, and the 
weight percent hydrogen peroxide, is presented in Table 16. The titration 
procedure used to determine the weight percent of H.sub.2 O.sub.2 in the 
complexes was as described in Example 12. Sodium carbonate H.sub.2 O.sub.2 
complex was purchased from Fluka Chemical Corp. The vapor-phase synthesis 
procedure used for synthesizing the inorganic peroxide complexes was the 
same as that disclosed in Example 12, with the exceptions that 10 g of the 
solid inorganic sample instead of 1-5 g, and two reaction cycles versus 
one, were employed. 
EXAMPLE 16 
The reaction procedure for liquid-phase synthesis of inorganic hydrogen 
peroxide complexes was essentially as described by Jones et al. (J. Chem. 
Soc., Dalton, 12:2526-2532, 1980). Briefly, inorganic solids were first 
dissolved in a 30% aqueous solution of hydrogen peroxide to make a 
saturated solution, followed by dropwise addition of ethanol. For the 
potassium oxalate and rubidium carbonate complexes, the white peroxide 
precipitates were formed as the amount of ethanol added was gradually 
increased. For potassium carbonate, potassium pyrophosphate and sodium 
pyrophosphate, the saturated solutions were incubated at -10.degree. C. 
for several hours to facilitate crystalline peroxide complex formation. 
The complexes were separated from the liquid by vacuum filtration, washed 
with ethanol at least three times and dried by vacuum. 
TABLE 16 
______________________________________ 
COMPOUNDS EVALUATED AND WEIGHT PERCENT HYDROGEN 
PEROXIDE PRESENT IN COMPLEXES 
Wt % H.sub.2 O.sub.2 
Chemical Chemical in Complexes.sup.1 
Name Formula Purchased.sup.2 
Vapor.sup.3 
Liquid.sup.3 
______________________________________ 
Sodium Carbonate 
Na.sub.2 CO.sub.3 
27.35 
Potassium Carbonate 
K.sub.2 CO.sub.3 7.43 22.70 
Robidium Carbonate 
Rb.sub.2 CO.sub.3 20.31 26.78 
Potassium Oxalate 
K.sub.2 C.sub.2 O.sub.4 
16.13 16.42 
Sodium Pyrophosphate 
Na.sub.4 P.sub.2 O.sub.7 
11.48 23.49 
Potassium Pyrophosphate 
K.sub.4 P.sub.2 O.sub.7 
20.90 32.76 
Sodium Orthophosphate 
Na.sub.3 PO.sub.4 15.67 
Potassium Orthophosphate 
K.sub.3 PO.sub.4 16.11 
______________________________________ 
.sup.1 The titration procedure employed to determine the weight percent o 
H.sub.2 O.sub.2 in the complexes is the same as the one stated in the 
previous patent application. 
.sup.2 Sodium carbonate hydrogen peroxide complex was purchased from Fluk 
Chemical Corp. 
.sup.3 The vapor and liquid phase procedures were used for synthesizing 
the inorganic peroxide. 
A differential scanning calorimeter (DSC) (Model PDSC 2920, TA instruments) 
was used to determine H.sub.2 O.sub.2 release or decomposition properties 
of the inorganic peroxide complexes. The DSC was run at a heating ramp of 
10.degree. C./min and at a temperature range of between 30.degree. C. and 
200.degree. C. under both atmospheric and varying vacuum pressure 
conditions. Referring now to FIG. 5, the DSC comprises a sample chamber 
110, heating plate 112 and pressure control system. The pressure control 
system comprises a pressure transducer 114 connected to a pressure gauge 
116. The pressure gauge 116 is connected to a controller 118 which is, in 
turn, connected to a pressure control valve 120. The pressure transducer 
114 is in fluid communication with pressure control valve 120 and with 
pump 122. 
Potassium oxalate hydrogen peroxide complex synthesized as described 
hereinabove was placed in a DSC and subjected to a particular vacuum 
pressure over a temperature range of 50.degree. C. to 170.degree. C. As 
can be seen in FIG. 6, greater release of H.sub.2 O.sub.2, an endothermic 
process, occurred at lower pressures, while the exothermic decomposition 
of H.sub.2 O.sub.2 was favored at higher pressures. The partial vacuum 
pressure is preferably less than 20 torr and most preferably less than 10 
torr. The actual pressure in the sample chamber is somewhat higher than 
that measured within the apparatus and the actual temperature of the 
chamber is somewhat lower than that measured of the metal plate or 
aluminum platen. Without wishing to be bound by any particular theory of 
operation, it is believed that the actual pressure used in the 
sterilization apparatus should be less than the vapor pressure of the 
inorganic peroxide complex at the actual temperature of the chamber in 
order to ensure that the complex will release hydrogen peroxide vapor with 
substantially no decomposition. However, in general, the pressure used is 
preferably less than 50 torr, more preferably less than 10 torr. In 
certain embodiments of the invention in which the vapor pressure of the 
peroxide complex is low, the pressure is preferably less than 5 torr. 
In the use of the inorganic peroxide complexes for sterilization, it is 
critical to complex stability that heating occur rapidly which may be 
effected by preheating the aluminum plate prior to contacting with the 
inorganic peroxide composition. In the use of the inorganic peroxide 
compounds, it is also preferred that the temperature be higher than 
86.degree. C. 
As discussed above, it is preferred that the inorganic hydrogen peroxide 
complex be heated rapidly, i.e. as rapidly as 1000.degree. C./minute or 
more. This can be accomplished by contacting the peroxide with a 
pre-heated heating plate. A preferred embodiment for accomplishing such 
rapid heating is shown in FIGS. 7A and 7B. Referring to FIG. 7A, there is 
shown an apparatus 125 for injecting peroxide vapor into a sterilization 
chamber 131 in a closed position. The inorganic hydrogen peroxide complex 
is incorporated into a peroxide disk 132. The disk 132 comprises five 
layers: three layers of CSR wrap, peroxide complex powder and aluminum 
foil coated with polypropylene. The disk 132 is heat sealed around its 
edge to retain the peroxide complex powder. The peroxide disk 132 is 
placed underneath a perforated aluminum plate 130 which is attached to 
housing 150 by aluminum attachment pieces 142. The disk 132 is loosely 
held in place between O-rings 151. Prior to introduction of peroxide vapor 
into the chamber, a heated aluminum platen 134 is apart from the peroxide 
disk 132 and is attached to an aluminum plate 136. A spring (not shown) 
within the bellow 138 holds the plate 136 down in the closed position. 
When the chamber 131 is evacuated, the bellow 138 is also evacuated. The 
plate 136 is seated against O-rings 148, thus separating a peroxide 
release chamber 152 from passageways 158. The apparatus is held in place 
and attached to a sterilization chamber 131 by bolts 144, 146, 154 and 
156. 
Referring to FIG. 7B, in order to bring the platen 134 up to contact the 
peroxide disk 132, the bellow 138 is vented. Once the pressure is 
increased, the bellow 138 moves upward, thereby propeling the heated 
aluminum platen 134 against the peroxide disk 132. In a preferred 
embodiment, the aluminum platen 134 is pre-heated to 175.degree. C.; 
however other temperatures can be used. Peroxide vapor is then released 
from the powder through the CSP layers, passes through the perforations 
160 in the perforated aluminum plate 130, and enters the peroxide release 
chamber 152. The upward movement of the heated aluminum platen 134 also 
opens the peroxide release chamber 152, allowing peroxide vapor to enter 
passageways 158 which are in fluid communication with the sterilization 
chamber. 
The inorganic peroxide complexes used in the following two examples to 
determine amount of peroxide release and sterilization efficacy were 
potassium pyrophosphate (K.sub.4 P.sub.2 O.sub.7.3H.sub.2 O.sub.2 :PP), 
potassium oxalate (K.sub.2 C.sub.2 O.sub.4.1H.sub.2 O.sub.2 :PO) and 
sodium carbonate (Na.sub.2 CO.sub.3.1.5H.sub.2 O.sub.2 :SC). 
EXAMPLE 17 
Release of Peroxide from SC, PO and PP 
The ideal temperature at which H.sub.2 O.sub.2 was released from SC, PO and 
PP was determined by DSC. The actual amount of H.sub.2 O.sub.2 released 
from 2 g of each of these complexes was determined at various temperatures 
using a 75 liter chamber and the apparatus of FIGS. 7A and 7B. The amount 
of H.sub.2 O.sub.2 released from the PP at 175.degree. C. was greater than 
for SC and PO. Although SC released the least amount of H.sub.2 O.sub.2 at 
175.degree. C., significantly more release was seen when the amount of 
sample was increased. 
TABLE 17 
______________________________________ 
RELEASE OF PEROXIDE IN 75 LITER CHAMBER 
SC PO PP 
______________________________________ 
Temp. to release H.sub.2 O.sub.2 
170.degree. C. 
150.degree. C. 
130.degree. C. 
(by DSC) 
With 2 grams sample 
At 125.degree. C. 
0.3 mg/L 0.8 mg/L 1.0 mg/L 
At 150.degree. C. 
1.2 mg/L 2.0 mg/L 1.5 mg/L 
At 175.degree. C. 
1.8 mg/L 2.5 mg/L 3.4 mg/L 
With 3 grams sample 
2.3 mg/L 
At 175.degree. C. 
With 4 grams sample 
2.9 mg/L 
At 175.degree. C. 
______________________________________ 
EXAMPLE 18 
Efficacy tests using SC, PO and PP 
2.times.10.sup.6 B. subtilis var. niger spores were inoculated on a SS 
blade. Three inoculated blades were first placed in the front, middle and 
back positions of a Spunguard wrapped 10".times.21".times.3.5" 
polyphenylene oxide tray. The wrapped tray was then placed in a 75 liter 
vacuum chamber having an initial vacuum pressure of 0.2 torr. A 5.5" 
peroxide disk was made by heatsealing the SC, SO or PP inorganic peroxide 
powders between three layers of Spunguard and one layer of aluminum foil 
coated with polypropylene film. The peroxide was released by contacting 
the disk for 2 minutes with an aluminum plate which had been preheated to 
175.degree. C., followed by an additional diffusion time of 8 minutes for 
a total exposure time of 10 minutes. After treatment, the three blades 
were separately placed in Trypticase Soy Broth (TSB) at 32.degree. C. for 
7 days and scored for bacterial growth. The results are summarized in 
Table 18. 
TABLE 18 
______________________________________ 
EFFICACY TEST RESULTS 
Peroxide Weight of Peroxide Sterility 
Complex Complex Conc. (+/all) 
______________________________________ 
PP 2 grams 3.4 mg/l 0/3 
PO 2 grams 2.5 mg/l 0/3 
SC 2 grams 1.8 mg/l 1/3 
SC 3 grams 2.3 mg/l 0/3 
SC 4 grams 2.9 mg/l 0/3 
______________________________________ 
As can be seen in the table, no growth of spores was observed with the 
exception of 2 g SC (1/3). However, when the amount of SC subjected to 
vaporization was increased to 3 grams, no bacterial growth was observed. 
These results underscore the efficacy of sterilization using inorganic 
hydrogen peroxide compound. 
Inorganic hydrogen peroxide complexes can be readily incorporated into the 
sterilization procedures described hereinabove in connection with organic 
peroxide complexes. For example, inorganic complexes can be used in 
connection with a plasma sterilization method, or in connection with a 
self-sterilizing enclosure where peroxide is slowly released from the 
complex. Similarly, inorganic complexes can also be used in the 
sterilization of articles having narrow lumens, whereby a vessel 
containing the inorganic peroxide complex is connected to the lumen. In 
addition, pressure pulsing of the vapor released from inorganic peroxide 
complexes can be employed. Other examples of the use of inorganic 
complexes for sterilization will be apparent to one having ordinary skill 
in the art upon reference to the present specification.