GB2292687A - Corrosion inhibition of oxidant-based anti-microbial compositions - Google Patents

Abstract

Items such as medical instruments (which may include brass, copper, aluminium, stainless steel, carbon steel or plastic parts) are microbially decontaminated (sterilised or disinfected) in an antimicrobial solution containing at least one corrosion inhibitor from the class consisting essentially of: benzotriazoles, tolyltriazoles, mercaptobenzathiazoles azoles, benzoates (eg salicylates), molybdates, phosphates chromates, dichromates, tungstates, vanadates, borates and benzoyl alanines. Powdered or liquid reagents containing such a corrosion inhibitor(s) are selected such that they react in the presence of a dissolving liquid (eg water) to form a strong oxidant solution in an appropriate concentration to be effective as an anti-microbial. Such reagents are advantageously stable during storage and handling. The preferred reagents include acetylsalicylic acid and sodium perborate (which react in the presence of water to form a peracetic acid solution and, moreover, sodium metaborate and salicylic acid, both of which inhibit corrosion of metal parts in the medical instruments). Disodium phosphate and benzotriazole may also be added. Sodium chlorate and an acid activator may be used to generate chlorine dioxide.

Description

CORROSION INHIBITION OF ANTI-MICROBIAL COMPOSITIONS BACKGROUND OF THE INVENTION Medical instruments can be sterilised in a steam autoclave. In hospitals and large facilities, medical instruments and equipment are transported to a central sterilising facility where they are sterilised under the supervision of sterilising room technicians. In a steam autoclave, the equipment is subject to superheated steam at high pressures, de pressurised, and cooled. One of the drawbacks of the steam autoclave is that many medical instruments cannot withstand the high temperatures and pressures. Another drawback resides in the one to two hour cycle time.

Instruments and equipment which cannot withstand the pressure or temperature of the autoclave can be commonly sterilised with ethylene oxide gas. The equipment is sealed in a sterilising chamber which is pressurised with the ethylene oxide gas. After an appropriate sterilising cycle, the equipment is degassed for twelve to sixteen hours in a vacuum or about 72 hours in ambient atmospheric conditions to remove the highly toxic ethylene oxide. One of the drawbacks to ethylene oxide sterilisation resided in-the long cycle times.

Another drawback resided in the need for training technicians to handle the highly toxic ethylene oxide gas systems. Yet another drawback is that some medical equipment cannot be sterilised with ethylene oxide gas.

Liquid sterilisation systems are utilised for equipment which will not withstand the high temperatures of steam sterilisation or are too expensive to use only once per day as is necessitated by the long sterilising times of ethylene oxide sterilisation. The equipment is immersed in a vat or tank that had been filled with a sterilising liquid, such as stabilised hydrogen peroxide, activated glutaraldehyde, chlorine dioxide or chlorine solution. Because such liquid sterilisation's are normally performed manually, the skill and care of the technician is a controlling factors in whether sterilisation or disinfection is, in fact, attained. In many instances, the technician is required to mix the components of the anti-microbial composition.Ewn when mixed properly, relatively long immersion times on the order of six to ten hours are commonly required to assure sterilisation.

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CORROSION INHIBITION OF ANTI-MICROBIAL COMPOSITIONS BACKGROUND OF THE INVENTION Moreover, many liquid sterilisation systems are highly corrosive to metal parts, particularly brass, copper, and aluminium. With long immersion times, even brass and stainless steel could be pitted and sharp cutting edges dulled; One advantage of the present invention is that it is stable during storage and handling. No special venting is required.

Another advantage of the present invention is that it provides an anti-microbial agent which quickly sterilises or disinfects medical equipment or the like, without causing corrosion. Another advantage is that it is compatible with all materials normally associated with medical devices.

DESCRIPTION Oxidising anti-microbial agents can be generated, such as chlorine dioxide, chlorine, hydrogen peroxide peracetic acid and mixtures thereof. More specifically, potassium chromates, sodium chloride, and phosphates may be mixed according to the following equation to produce a strong chlorine oxidant on the addition of water.

K2Cr207+6NACl+7H3FO K2}{P04+Cr2N(}{P04)3+HOCl+6H+ + H20 Optionally, excess dichromate and an organic corrosion inhibitor may be provided for improved buffering and corrosion inhibiting.

Hydrogen peroxide and an inorganic inhibitor can be generated: NaO3+H2 0+ H3P04+H202+NaBO2+H3P04 Similarly, chlorine dioxide can be generated from powdered ingredients on the addition of water: 2NaC10 +LiClO+H O-2C10 NaOH+NaC1- +liOH A mixed biocide system can be achieved by adding sodium chloride to the peracetic acid reaction to produce hypochlorous acid.

CH OOOOH + Na +C - CH OOONa+HOCl Excess peracetic acid is deliberately present such that both peracetic acid and hypochlorous acid are present in the biocidal solution.

In these compositions, it is preferable to add additional corrosion inhibitors and buffers to protect copper, brass, aluminium, steel and the like. Preferably, corrosion inhibitors are added which result in three corrosion inhibitors in the final solution. One is an organic inhibitor, one is an inorganic inhibitor, and the third can be either.

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CORROSION INHIBITION OF ANThMlCROBIAL COMPOSITIONS DESCRIPTION The copper and brass corrosion inhibitors are preferably beniotriazoles and tolytriazoles, which are preferred due to their stability in the presence of strong oxidising compounds. Mercaptobenzathiozol might also be utilised but is more apt to be oxidised or de stabilised by strong oxidisers.

Azoles, benzoate's, and other five membered ring compounds may also prove acceptable as copper and brass corrosion inhibitors.

By way of example, the anti-corrosive buffering compounds may include a mixture of phosphate in sufficient volume to produce a final concentration of 1.25% weight per Volume and molybdates in an appropriate amount to produce a final solution of 0.011% weight per volume. Phosphates may also be effective in the range of 0.2% to 12% and the molybdates may be effective from 0.1% to 10%. Optionally, chromate's , dichromate's, tungstates, vanadates, other borate's, and combinations thereof, may be substituted in appropriate concentrations to inhibit steel corrosion and aluminium corrosion.

In hard water, the phosphates tend to cause calcium and magnesium salts to precipitate and coat the instruments being sterilised and parts of the sterilising system.

A sequestering agent appropriate to prevent precipitation, such as sodium hexametaphosphate, may be provided. Of course, if de ionised or soft water is utilised the sequestering agent may be eliminated. However, to ensure universal applicability with any water that might be utilised, the presence of a sequestering agent is preferred.

A wetting agent present from 0.001 to 1.0% (w/v) improves the wetting of the surface of the instrument by the anti-microbial agent. The wetting agent has also been found to increase penetration of the anti-microbials improving antimicrobial efficacy while reducing corrosion.

The following are examples that illustrate the corrosion inhibiting effectiveness of various strong oxidant anti-microbial formulations. Coupons of 410 stainless steel, brass (ASTM B36-C 2600), aluminium (5052 - H32), and carbon steel scalpel blades were exposed to two changes of sterilant mix for a total of four hours exposure at 50 - 55 C. One set of coupons was run in distilled water and a sterilant mix (0.5% sodium perborate and 0.5% aspirin) and a second set in tap water and sterilant mix. A second set of tests was performed using brass and aluminium coupons, and carbon steel scalpel blades in a matrix with concentration of disodium phosphate of 0. 0.2, 0.4, 0.5, and 0.7% and concentrations of benzotriazole of 0, 0.001, 0.005, 0.01 and 0.02%. Each type of coupons were exposed to sterilant mix and additives for three hours at 50-55 C. All coupons were rinsed well with distilled water and acetone and allowed to dry before evaluation.

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CORROSION INHIBITION OF ANTI-MICROBIAL COMPOSITIONS DESCRIPTION Corrosion or discoloration was noted on all materials using just the basic peracetic acid, sodium metaborate, and salicylic acid solution. Carbon steel and 410 stainless steel showed only minor corrosion. Aluminium was discoloured and showed some pitting. Brass was heavily corroded on most surfaces and showed some pitting. In the matrix, the addition of 0.001% benzotriazole or 0.4% phosphate eliminated corrosion on carbon steel. The addition of 0.4% phosphate eliminated corrosion on aluminium. For brass, the addition of 0.25 PHOSPHATE OR 0.05 benzotriazole eliminated pitting corrosion. However, phosphate caused darkening of brass which was apparent unless 0.02 benzotriazole was added. Random spotting of brass occurred at all concentrations. This sort of corrosion can be eliminated by adding a surfactant.

The invention has been described with reference to the preferred embodiments.

Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention can be construed as including all such alterations and modification insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims (1)

1. (1) A method of microbially decontaminating items, the method comprising: measuring selected quantities of powdered or liquid ingredients which form an oxidant that kills at least pathogenic micro-organisms when mixed with a dissolving liquid and at least one corrosion inhibitor from the class consisting essentially of: benzotriazoles, tolytriazoles, mercaptobensathiozol, azoles, benzoate, molybdates, phosphates,chromates, dichromate's, tungstate,vanadate,and borate; (2) Holding the powered or liquid ingredients in a container until an item is to be microbially decontaminated; (3) Opening the container and dissolving the powdered or liquid ingredients in the dissolving liquid such that an anti-microbially effective solution of the pathogenic micro-organism killing oxidant and corrosion inhibitors is formed; (4) Immersing the item in the solution at least until the pathogenic microorganisms are killed; and rinsing the item.

   (5) A cleaning disinfectant sterilant powder or solution that contains benzoyl alanines as corrosion inhibitors from 0.001% - 1.0% based on WT of final aqueous use solution.