GB2137882A - Disinfectants Containing Magnesium Peroxycarboxylate - Google Patents

Abstract

A broad spectrum disinfectant/sterilising agent comprises an alkanolic solution of a magnesium salt of an aryl, cycloaliphatic or conjugated aliphatic carboxylic acid, substituted by one or more peroxycarboxylic acid groups. The preferred salt is magnesium monoperoxyphthalate, and especially having an avox concentration of at least 400, particularly up to 2000 ppm. Solid compositions for transportation and storage that can be dissolved in the alkanol to generate the disinfecting/sterilising solution can include anionic or cationic surfactants, builders, sequestrants, and stabilisers etc. The compositions useful disinfecting/sterilising hard surfaces, particularly in medical/veterinary or food processing environments or in toilets or drains, whether in the home or in industry.

Description

SPECIFICATION Sterilisation/Disinfection The present invention relates to sterilisation/disinfection and in particular, to processes and compositions for sterilising/disinfecting, including inter alia non-absorptive surfaces, in particular employing a peroxygen compound therefore.

Man shares his environment with a myriad of micro-organisms, often somewhat unwillingly, and in consequence a considerable effort has been devoted to locating chemical sterilising agents or disinfectants especially for use in locations where food or drink is prepared, stored or served, or in hospitals or other places where humans or animais are being treated for injuries or disease. Yet further areas of potential contact include lavatories, washing facilities or domestic or industrial waste disposal drains. In order to seek to sterilise or disinfect the aforementioned or other non-absorptive surfaces, sometimes referred to in the literature as hard surfaces, there is a widespread practice of bringing into contact with such surfaces a liquid, often an aqueous solution containing one or more sterilising or disinfecting agents.

Many of the agents that have been employed hitherto could be classified within the general headings of phenolics, quaternary ammonium compounds, aldehydes, active chlorine compounds and peroxygen compounds. There are, however, disadvantages associated with the various classes of compounds. Thus, many of the phenolics are significantly poisonous to mammals, including humans, can induce corrosion of metallic surfaces, and can have a powerful smell to which many people object.

The quaternary ammonium compounds, on the whole, demonstrate poor activity against bacterial spores and have a restricted activity against such commonly encountered bacteria as Pseudomonas species, with the net result being that they are of somewhat restricted applicability. There is increasing evidence to suggest that aldehydes, although regarded by many as very effective, can act as human skin sensitisers or even induce cancer in humans. Active chlorine compounds, such as sodium hypochlorite, although cheap to produce can be rapidly inactivated by organic contaminants, can induce corrosion especially on steel equipment and once again therefore have only limited applicability.

Of the peroxygen compounds, hydrogen peroxide has long been recognised as being a bacteriostat rather that a bactericide, whereas the more powerful peractive acid in many grades is dangerous or at least unpleasant to dilute down to use concentrations and also suffers from an unpieasant smell.

Accordingly, there remains a need for an alternative sterilising agent/disinfectant which can act against a broad spectrum of micro-organisms of general interest in medical or industrial situations including both Gram-positive and Gram-negative bacteria, spore-forming bacteria and yeasts.

It is an object of the present invention to provide a process and/or compositions for sterilising/disinfecting that ameliorates to at least some extent some or all of the aforementioned disadvantages.

It is a further object to provide compositions in solid form, thereby minimising transport costs and avoiding the transport of unnecessary volumes of water acting as diluent or carrier.

According to the present invention there is provided a process for sterilising and/or disinfecting a hard surface characterised by bringing into contact with that surface a liquid medium containing as active ingredient an effective amount of one or more magnesium salts obeying the general formula: Class (1)-an aromatic carbocyclic compound substituted around the aromatic nucleus by a carboxylate group and a peroxycarboxylic acid group both groups being derivable from the corresponding aromatic carbocyclic an hydride by reaction with hydrogen peroxide, said aromatic carboxylic compound optionally being further substituted by at least one of the groups selected from alkyl, carboxylate, sulphonate, nitro, chloro and bromo groups or Class (2)-a cycloaliphatic compound substituted around the cycloaliphatic nucleus by a carboxylate group and a peroxycarboxylic acid group both groups being derivable from the corresponding cycloaliphatic carbocyclic anhydride by reaction with hydrogen peroxide, said cycloaliphatic carboxylic compound optionally being further substituted by at least one of the groups selected from alkyl, carboxylate, sulphonate, nitro, chloro and bromo groups or Class (3)-an olefinically unsaturated aliphatic compound substituted by a carboxylate group and a peroxycarboxylic acid group, the carbonyl group of the carboxylate substituent being conjugated with the carbonyl group of the peroxycarboxylic acid via the olefinic unsaturation within the aliphatic compound, both substituents being derivable from the corresponding anhydride by reaction with the hydrogen peroxide and maintaining contact between the medium and the surface until at least some of the micro-organisms have been killed.

By the term "effective amount" herein is meant a concentration of the magnesium salt which leads within an acceptable period to the significant reduction in the microbial contamination of the hard surface. It will be fully recognised that the effective amount will tend to vary to at least some extent depending upon external conditions such as temperature, the presence or absence of stabilisers or decomposition catalysts for the peroxygen compound, the presence or otherwise of any other bactericidal or inhibiting compound, and the solution characteristics including, in particular, its pH.

However, it is especially desirable to employ a concentration of the magnesium salt of at least 200 ppm avox, that is to say available oxygen from the persalt. Such a minimum concentration can be provided by a concentration of about 3.5 gpl hydrated magnesium monoperoxyphthalate, i.e. the compound having the formula Mg2t(HO3CC6H4CO7)2 . 6H20, which in manufacture tends to have an avox content of about 6%. The corresponding concentration of the other magnesium salts required to yield the avox concentration in solution can readily be obtained by calculation, but taking into account the number of percarboxylic acid groups per organic molecule and the general formula of the compound, or more practically by measuring the avox content of the solid starting material using a standard peracid method of determination.In many instances, it is preferable to employ an avox concentration somewhat higher than the aforesaid minimum, such as at least 400 ppm avox. In view of the high solubility of the magnesium compounds in water, even at ambient temperature, very high avox concentrations can be obtained, if desired, in some cases even up to 10,000 ppm. Convenient concentration ranges are often from 500 to 2,000 ppm avox although, of course, such ranges typically apply when the magnesium persalt is the sole bactericide, and these amounts can be scaled down should some further bactericide be employed in co-operation with the magnesium persalt.

To a certain extent, the period of contact between the bactericide and the hard surface is at the discretion of the user and depends upon the extent to which the user wishes to micro-organisms to be reduced in number. As is fully understood, the rate of kill depends in particular upon the temperature of the hard surface/sterilising fluid interface, and the concentration of active ingredient in the sterilising/disinfecting fluid. For any given reduction in micro-organism count, the desired period of contact can be reduced by either or both of increasing the concentration of the magnesium persalt or by increasing temperature.If desired, the interface temperature can be any at which the solution of magnesium persalt remains in liquid form, but in practice is often selected within the range of 5 600 C. Conveniently, this temperature range encompasses the general variation in ambient temperatures for hard surfaces encountered in domestic, industrial or medical locations. For purposes of convenience only, reference herein is made to desirable minimum contact times at 20-250C but the correspondingly longer or shorter contact time can readily be determined if alternative temperatures are employed.It is especially suitable to maintain a contact of at least 10 minutes when employing solutions having a concentration of avox at the lower end, that is to say of around 400500 ppm avox where the predominating micro-organisms are either asporogenous bacteria or yeasts, but to employ a substantially longer period, for example at least overnight and preferably at least 24 hours in the case of spore/forming bacteria, since such/spore forming bacteria are especially difficult to kill. If shorter times than the desired minimum are employed, the result will tend to be a somewhat reduced kill of the micro-organisms.In practice, therefore, it is often respecially convenient to employ a contact time in the region of from 5 to 20 minutes or longer at the discretion of the user, employing solutions of magnesium persalt having an avox concentration selected within the range of from 4002,000 ppm avox at a temperature from 20-300C for surfaces contaminated with other than sporeforming bacteria. At the end of the contact period, the surface can be rinsed, if desired. Naturally, a preliminary investigation as to which micro-organisms are present initially is desirable.

Various methods of bringing the hard surface and sterilisfng/disinfecting medium into contact can be employed. In one method, which is particularly applicable when the hard surfaces in the form of small objects, the surface is immersed in a bath of the sterilising/disinfecting fluid. In the case of somewhat larger surfaces, where immersion becomes less practical, the fluid can be poured or sprayed onto the surface, either continuously or intermittently, possibly with the fluid after collection in a holding tank underneath then being recycled. Alternatively, a thickening agent can be incorporated within the sterilising/disinfecting fluid so as to retard the separation of the fluid from the surface under gravity or other influences.Of course, in the case of baths of sterilising fluid, the avox content thereof can be periodically monitored and augmented as desired by introduction of fresh magnesium persalt.

Conveniently, magnesium persalt sterilisers/disinfectants demonstrate activity at both mildly acidic and mildly alkaline conditions as well as under neutral conditions. It is preferable to employ the persalt in solutions having a pH of from pH 5 to pH 9 and especially within a pH selected in the range of 5 to 7. A pH within those ranges can be maintained by several methods. In one method, the sterilising/disinfecting fluid contains one or more buffering agents for example sodium potassium hydrogen phosphate which are known to buffer within the desired pH range.An alternative way, at least in the case of baths, is to monitor the pH and link that monitoring to a dispenser for acid such as a mineral or food acid, preferably other than hydrochloric acid, or an alkali such as sodium hydroxide solution or sodium carbonate solution depending upon how the sterilising/disinfecting fluid was varying from the preferred pH.

The sterilising fluid is preferably prepared by dissoiving in an available supply of water the magnesium salt in solid form. Since the magnesium salt dissolves very quickly, there is no need to prepare many days supply at once, but indeed it is preferable to employ the made-up solution at a time commencing within a day or so after its preparation. It will be recognised therefore that advantage is thereby taken from the fact that the active ingredient is readily stored and transported in the solid form in which it exhibits remarkable stability for a peroxyacid compound, not only with respect to thermal shock our temperature shock, but also shows excellent resistance to decomposition from encounter with environmental air.Naturally, the use of a solid during storage minimises problems of spillage and mitigates the need for specially vented containers as is often required for other and liquid peroxygen compositions or active chlorine compositions.

Although the magnesium persalt can be employed by itself, it can be desirable to incorporate with it one or more other ingredients such as pH buffers, as aforementioned, and/or one or more cationic or anionic surfactants, and/or in small amounts compounds such as sequestrants, peracid stabilisers, a redox indicator, or perfume. Moreover, a diluent or bulking agent, such as sodium or magnesium sulphate can be incorporated if desired.Consequently, compositions contemplated within the present invention include those containing per part by weight of the magnesium persalt, up to two parts of an anionic or cationic surfactant and particularly from 0.1 to 1 part by weight of the aforesaid surfactant, up to 2 parts by weight of buffer and especially a buffer capable of maintaining a pH of from 5 to 7, and a minor proportion, if desired, of one or more of the seqeustrant, stabiliser, or redox indicator. Examples of anionic surfactants include natural or synthetic sodium or potassium soaps, alcohol sulphates, alkylaryl sulphonates, olefin sulphates or sulphonates, alcohol ether sulphonates, and phosphated alkyl or alkaryl ethoxolates, sulphosuccinates and alkane sulphonates amongst others.A much more complete range of anionic alternatives can be found in a standard work on surfactants, such as that by Schwartz and Perry. Likewise, examples of suitable cationic surfactants include the known classes quaternary ammonium salts, including alkyl pyridinium halides, generally containing at least 11 carbon atoms and optionally including phenoxy and/or ethoxy linkage, and amine acetates.

Additionally, the sterilising fluid can contain if desired for some other reason, such as to aid wetting of the surface or to assist cleansing of the surface, additionally or alternatively one or more nonionic surfactants (though their use is not preferred), and/or one or more water soluble of insoluble builders, for example phosphates, or polycarboxy organic complexing agent or alumina silicates conveniently in each case in an amount of from zero to two parts per part of magnesium persalt. If desired, the composition can also include one or more abrasives, again in an amount of up to two parts per part of the persalt, thereby enabling the composition readily to be employed in conjunction with the limited amount of diluent water as a bactericidal scouring powder.

The aforementioned compositions can readily be produced in a variety of convenient forms, including tablets, pills, powders, granules or agglomerates. Alternatively they can be incorporated into sheets or foams. The compositions, therefore, are easy to use in readily controllable amounts either for the domestic or medical or industrial user.

Whilst for many uses, the liquid medium which contains the magnesium persalt is conveniently water, it can be advantageous for the medium to comprise at least a minor proportion of a low molecular weight aliphatic alcohol, such as 10 to 80% and particularly 25 to 40% w/w solution of alcohol in water. By so doing the resultant combination of the magnesium persalt and alcohol exhibits enhanced sporicidal properties. It is preferable to employ a weight ratio of alcohol to the magnesium persaltoffrom 10:1 to 100:1, especially with at least 0.2% w/w persalt, although some effect is noticeable outside that preferred range. The alcohol desirably contains 1 to 4 carbon atoms, and up to 3 hydroxyl groups or mixtures of two or more thereof. Ethanol, isopropanol and propanol are especially preferred.Such solutions are particularly useful for disinfecting/sterilising articles such as surgical instruments that can be immersed therein. Naturally the solutions can be regenerated by introduction periodically of additional magnesium persalt.

The hard surfaces that can be disinfected and/or sterilised by use of compositions described herein range from the sterilisation of~medical instruments through food processing apparatus or equipment to in-place sterilisations or disinfection of work surfaces, walls and floors, toilets, baths, basins and bidets, and the waste pipe work leading from them. Such surfaces can be made from a very wide range of materials including metals such as stainless steel, wood, plastics, glass, ceramics or paints. It is a particular feature that the compositions can be used for'heat sensitive equipment, fibre optics and metals demonstrating that the active ingredient exhibits not only a broad spectrum in respect of the micro-organisms which it kills but also in respect of the surfaces which can be treated safely with it.

Having described the invention in general terms, specific examples hereof will now be given by way of example only.

In order to assess the effectiveness of the maynesium persalts as a broad spectrum biocide, cultures of a range of standard strains of bacteria and yeasts were prepared. The species used were Bacillus subtilis NCTC 10452 (Bs) Escherichia coli NCTC 8196 (Ec) Klebsiella pneumoniae ATCC 4352 (Kp) Pseudomonas aeruginosa ATCC 1 5442 (Pa) Staphylococcus aureus ATCC 6538 (Sa) Streptococcusfaecalis ATCC 10541 (Sf) Candida albicans ATCC 10231 (Ca) Saccharomyces cerevisiae NCYC 1026 (Sc) The asporogenous bacteria were maintained by daily seriai sub-culture in Nutrient Broth (Oxoid), fresh cultures being started from stock cultures after ten sub-cultures.Spore-forming bacteria were similarly treated, serial sub-culture being carried out in a sporulation broth consisting of 10 g L-1 peptone (Difco) and 20 mg L-l manganese (II) sulphate. At fortnightly intervals all the species of bacteria were checked using the API 20B system to ensure that their properties had not changed. The fungi were sub-cultured every two days in Sabouraud Liquid Medium (Oxoid), with fresh cultures again being started from stock cultures after ten serial sub-cultures.

For experimental purposes the following were used: asporogenous bacteria: 24 hr culture at 370C in Nutrient Broth spore-forming bacteria: 10 day culture at 370C in the sporulation broth.

fungi: 72 hour culture at 250C in Sabouraud Liquid Medium.

In no case was the culture direct from the stock culture used for experimental purposes.

In each run, a sample of water was prepared containing if desired, interfering or co-operating substance as specified in the following Tables and sufficient magnesium persalt to produce an avox of approximately 300, 600 or 1200 ppm, i.e. respectively 0.5% by weight concentration of solid hydrated magnesium monoperoxyphthalate having an avox of 6%, or 1% concentration of the salt or 2% concentration of the salt and the selected strain of micro-organism was introduced at 21 0C and held at that temperature for the test. After the selected contact period biocidal activity was halted by transferring a sample into a solution of a neutraliser.

It will be recognised that the method used to determine the activity of the biocide resembled closely French standard NFT 72-i 70 of.March 1981, incorporated herein by reference. In the case of the magnesium persalts, the neutraliser solution was sodium thiosulphate. Samples from the neutralised solution and then plated out and the logarithmic reduction factor (LRF) was then calculated by comparing the number of surviving micro-organisms with the number originally present. The LRF is given in the Tables.

The range of diluents and potential interfering substances comprised buffering the aqueous medium to either pH 5.0, pH 7.0, pH 9.0 by a buffer comprising sodium acetate drihydrate, sodium borate decahydrate and dipotassium hydrogen phosphate in a weight ratio of 14:38:17.5, with subsequent adjustment of pK by addition as appropriate of 2.5 m H2SO4 or 5 m NaOH solution. A second set of potential interferring substances comprised sodium carbonate, at a concentration of 0.3 gpl, sodium tripolyphosphate (STPP) at 2.1 5 gpl, sodium metasilicate (silicate) at 1.20 gpl, and sodium sulphate at 0.85 gpl. It will be recognised that these are either builders or bulking agents. Examples of surfactants comprised a cationic surfactant at 1.0 gpl, namely diisobutylthinoxyethoxyethyldimethylbenzyl ammonium chloride (HYAMINE 16-22), a nonionic surfactant was polyoxyethylene (20) sorbitan, mono oleate at 0.5 gpl (TWEEN 80) and an anionic surfactant of sodium dodecylbenzene sulphonate at 1.0 gpl, (NANSA 30) representative organic substances comprised bovine serum at 1 %m/v (OXOID SR33), yeast extract at 0.4 %m/v (OXOID L21) defibrinated horseblood at 5 %m/v (OXOID SR50) and tryptic digest of casein at 0.4 %m/v (OXOID L42). HYAMINE, TWEEN, NANSA AND OXOID are all trademarks.

TABLE 1 Antimicrobial Activity of 0.5%-300 ppm Avox LRF Values

Species | Bs Bs Bs Ca Ec Kp Pa Sc Sa Sf Time/min 60 300 1440 10 10 . 10 10 10 10 Aqueous system clean (i) < 1.8 < 1.8 < 1.8 < 1.9 > 5.8 > 5.7- > 6.5 > 4.8 > 5.9 > 5.0 clean (ii) < 1.8 < 1.8 2.02 < 1.9 > 6.2 > 6.0 > 6.5 > 4.4 > 5.2 > 6.0 clean mean < 1.8 < 1.8 < 1.9 < 1.9 > 6.0 > 5.9 > 6.5 > 4.6 > 5.6 > 5.5 hard water < 1.8 < 1.8 4.32 < 2.2 > 5.6 > 6.4 > 6.4 > 4.4 > 5.2 > 6.0 pH 5.0 < 1.7 < 1.7 < 1.7 < 2.3 > 6.3 > 6.2 > 6.2 > 4.5 > 5.6 > 6.3 pH 7.0 < 1.7 < 1.7 < 1.7 < 2.2 > 5.7 5.69 > 6.8 < 1.8 < 2.3 > 5.8 pH 9.0 < 1.7 < 1.7 < 1.7 < 2.0 4.33 4.51 < 3.8 > 4.2 < 2.2 < 3.5 carbonate < 3.5 < 3.5 < 3.5 < 2.2 > 6.4 > 5.8 > 6.4 < 2.0 < 2.7 < 3.6 STPP < 3.5 < 3.5 < 3.5 < 2.1 > 6.0 > 6.3 6.10 2.89 4.50 > 6.3 silicate < 3.5 < 3.5 < 3.5 < 2.2 > 6.4 > 6.3 > 6.2 < 1.3 < 2.9 5.49 sulphate < 3.5 < 3.5 < 3.5 < 2.1 > 6.3 > 6.4 > 6.6 > 4.5 > 5.9 > 6.6 Cationic > 6.0 < 3.3 4.58 > 4.7 > 6.2 > 6.5 > 6.4 > 4.6. > 5.7 > 6.3 non-ionic < 3.3 < 3.3 < 3.3 < 2.1 > 6.2 > 6.6 > 6.7 3.38 > 5.4 > 6.5 anionic < 3.3 < 3.3 < 3.3 > 4.9 > 6.1 > 6.9 > 6.5 > 4.6 > 5.5 > 6.5 serum < 3.3 < 3.3 < 3.3 < 2.0 > 5.7 > 6.7 > 6.5 3.89 > 5.7 > 6.4 yeast < 3.3 < 3.3 < 3.3 < 2.1 > 6.5 > 6.5 > 6.5 3.44 4.75 4.14 blood < 3.3 < 3.3 < 3.3 < 2.0 > 5.7- > 6.7 > 6.5 < 1.8 > 5.7 > 6.4 casein < 3.3 - < 3.3 < 3.3 < 2.3 > 6.2 > 6.4 > 6;3 < 1.9 4.88 4.75 natural pH=4.95 TABLE 2 Antimicrobial Activity of 1.00/0--600 ppm Avox LRF Values

Species Bs Bs Bs Ca Ec Kp Pa Sc Sa Sf Time/min 60 300 1440 10 10 10 10 10 10 10 Aqueous system clean (i) < 1.8 < 1.8 < 1.8 < 1.9 > 5.8 > 5.7 > 6.5 > 4.8 > 5.9 > 5.0 clean (ii) < 1.8 < 1.8 1.92 3.09 > 6.2 > 6.0 > 6.5 > 4.4 > 5.2 > 6.0 clean mean < 1.8 < 1.8 < 1.9 < 2.5 > 6.0 > 5.9 > 6.5 > 4.6 > 5.6 > 5.5 hard water < 1.8 < 1.8 > 4.5 > 4.9 > 5.6 > 6.4 > 6.4 > 4.4 > 5.2 > 6.0 pH 5.0 < 1.7 < 1.7 > 4.4 > 5.0 > 6.3 > 6.2 > 6.2 > 4.5 > 5.6 > 6.3 pH 7.0 < 1.7 < 1.7 < 1.7 < 2.2 > 5.7 > 6.0 > 6.8 < 1.8 > 5.0 > 5.8 pH 9.0 < 1.7 < 1.7 < 1.7 < 2.0 > 5.9 > 6.1 3.83 > 4.2 < 2.2 < 3.5 carbonate < 3.5 < 3.5 < 3.5 < 2.2 > 6.4 > 5.8 > 6.4 > 4.7 > 5.4 > 6.3 STPP < 3.5 < 3.5 < 3.5 < 2.1 > 6.0 > 6.3 > 6.7 > 4.6 > 5.8 > 6.3 silicate < 3.5 < 3.5 < 3.5 < 2.2 > 6.4 > 6.3 > 6.2 3.60 5.34 > 6.2 sulphate < 3.5 < 3.5 < 3.5 < 2.1 > 6.3 > 6.4 > 6.6 > 4.5 > 5.9 > 6.6 Cationic 3.60 < 3.3 5.52 > 4.7 > 6.2 > 6.5 > 6.4 > 4.6 > 5.7 > 6.3 non-ionic < 3.3 < 3.3 < 3.3 < 2.1 > 6.2 > 6.6 > 6.7 > 4.7 > 5.4 > 6.5 anionic < 3.3 < 3.3 < 3.3 - > 4.9 > 6.1 > 6.9 > 6.5 > 4.6 > 5.5 > 6.5 serum < 3.3 < 3.3 3.99 < 2.0 > 5.7 > 6.7 > 6.5 4.19 > 5.7 > 6.4 yeast < 3.3 < 3.3 4.16 < 2.1 > 6.5 > 6.5 > 6.5 > 4.6 > 5.2 > 5.8 blood < 3.3 < 3.3 < 3.3 < 2.0 > 5.7 > 6.7 > 6.5 > 4.5 > 5.7 > 6.4 casein < 3.3 < 3.3 4.82 < 2.3 > 6.2 > 6.4 > 6.3 3.41 > 5.2 > 6.1 natural pH=4.82 TABLE 3 Antimicrobial Activity of 2.0%--1 200 ppm Avox LRF Values

Species Bs Bs Bs Ca Ec Kp Pa Sc Sa Sf Time/min 60 300 1440 10 10 10 10 10 10 10 Aqueous system clean (i) < 1.8 < 1.8 > 4.5 > 4.6 > 5.8 > 5.7 > 6.5 > 4.8 > 5.9 > 5.0 clean (ii) < 1.8 < 1.8 > 4.5 > 4.6 > 6.2 > 6.0 > 6.5 > 4.4 > 5.2 > 6.0 clean mean < 1.8 > 1.8 > 4.5 > 4.6 > 6.0 1 > 5.9 > 65 > 4.6 > 5.5 > 5.5 hard water < 1.8 4.22 > 4.5 > 4.9 > 5.6 > 6.4 > 6.4 > 4.4 > 5.2 > 6.0 pH 5.0 < 1.7 < 1.7 > 4.4 > 5.0 > 6.3 > 6.2 > 6.2 > 4.5 > 5.6 > 6.3 pH 7.0 < 1.7 < 1.7 > 4.4 < 2.2 > 5.7 > 6.0 > 6.8 3.68 > 5.0 > 5.8 pH 9.0 < 1.7 < 1.7 < 1.7 < 2.0 > 5.9 > 6.1 > 6.5 > 4.2 < 2.2 > 6.2 carbonate < 3.5 < 3.5 > 6.2 > 4.9 > 6.4 > 5.8 > 6.4 > 4.7 > 5.4 > 6.3 STPP < 3.5 < 3.5 > 6.2 3.44 > 6.0 > 6.3 > 6.7 > 4.6 > 5.8 > 6.3 silicate < 3.5 < 3.5 > 6.2 3.61 > 6.4 > 6.3 > 6.2 > 4.0 > 5.6 > 6.2 sulphate < 3.5 < 3.5 > 6.2 > 4.8 > 6.3 - > 6.4 > 6.6 > 4.5 > 5.9 > 6.6 Cationic < 3.3 < 3.3 > 6.0 > 4.7 > 6.2 > 6.5 > 6.4 > 4.6 > 5.7 > 6.3 non-ionic < 3.3 < 3.3 5.82 3.59 > 6.2 > 6.6 > 6.7 > 4.7 > 5.4 > 6.5 anionic < 3.3 < 3.3 3.72 < 4.9 > 6.1 > 6.9 > 6.5 > 4.6 > 5.5 > 6.5 serum < 3.3 < 3.3 > 6.0 ~ 2.83 > 5.7 > 6.7 > 6.5 > 4.5 > 5.7 > 6.4 yeast < 3.3 < 3.3 > 6.0 3.56 > 6.5 > 6.5 > 6.5 > 4.6 > 5.2 > 5.8 blood < 3.3 < 3.3 > 6.0 > 4.7 > 5.7 > 6.7 > 6.5 > 4.5 > 5.7 > 6.4 casein < 3.3 < 3.3 > 6.0 < 2.3 > 6.2 > 6.4 > 6.3 > 4.6 > 5.2 > 6.1 natural pH=4.80 From the foregoing Tables, it will be recognised that the effectiveness as a biocide of magnesium monoperoxyphthalate, which is selected as a typical magnesium persalt, increased as its concentration in solution increased from 300 to 1200 ppm avox. Even at the 300 ppm avox concentration, greater than 99.999% reduction was achieved against the asporogenous bacteria, although the somewhat higher concentrations were preferable for the spos:W-forming bacteria and the yeasts. It will be observed that the biocide could tolerate readily hard water and was particularly effective in the pH range of pH 5 to 7, although to at least some extent pH 9 could be tolerated.The various potentially interferring substances seemed not to impair the effectiveness of the biocide within experimentally significant limits, and indeed, the evidence would suggest that the cationic surfactant co-operated with and promoted the biocidal activity of the magnesium persalt. It will be further recognised, therefore, that the various aforementioned substances can be incorporated in biocidal compositions containing the magnesium persalt, so as to combine the biocidal activity of the persalt whilst including the cleansing or stain removing properties of the other substance like the surfactant and/or builder. Furthermore, the non-interference from blood, serum casein or yeast demonstrates the suitability of using the magnesium persalt in such hostile environments as abbatoirs as well as in food processing environments, medical or vetinerary establishments, or in the home.

The tests on clean systems were repeated using solutions of magnesium monoperoxyphthalate (2%, 1200 ppm avox) which had been stored for varying periods before use. These results are summarised in Table 4.

From Table 4, it can be seen that its effectiveness as a biocide remained the same throughout the working day, but there was some impairment after 24 hours storage with respect to Candida albicans, and thereafter there was a gradual deterioration in respect of the spore-forming bacteria. For asporogenous bacteria, the biocide remained active for the entire test period of a month storage. In Table 4 the term exposure represents the duration of exposure of the species to the biocide.

TABLE 4 Effect of Age on Antimicrobial Activity LRF Values 2%1200 ppm Avox

Species Bs Bs Bs Ca Ec Kp Pa Sc Sa Sf exposure (mins) 60 300 1440 10 10 10 10 10 10 10 age of solution 30 minutes < 2.5 < 2.5 3.38 3.71 > 5.5 > 6.2 > 6.5 > 4.8 > 5.4 > 6.2 2 hours , < 2.5 < 2.5 3.31 4.08 > 5.5 > 6.2 > 6.5 > 4.8 > 5.4 > 6.2 5 hours < 2.5 ND 3.43 3.42 > 5.5 > 6.2 > 6.5 > 4.8 > 5.4 > 6.2 8 hours ND ND 3.51 3.23 > 5.5 > 6.2 > 6.5 > 4.8 5.00 > 6.2 24 hours < 2.5 < 2.5 3.02 < 1.8 > 6.2 > 5.9 5.76 > 4.2 > 5.5 > 6.3 7 days < 2.5 < 2.5 < 2.5 < 1.8 > 6.2 > 5.9 > 6.-4 < 1.5 < 2.8 < 3.6 14 days < 2.5 < 2.5 < 2.5 < 2.0 > 5.5 > 6.2 5.05 > 4.8 < 2.7 < 3.5 28 days < 2.5 < 2.5 - < 2.5 < 2.0 > 5.5 5.44 6.15 > 4.8 < 2.7 < 3.5

Claims (14)

1. A process for sterilising and/or disinfecting a hard surface characterised by bringing into contact with that surface a liquid medium containing as active ingredient an effective amount of one or more magnesium salts obeying the general formula: Class (1) an aromatic carbocyclic compound substituted around the aromatic nucleus by a carboxylate group and a peroxycarboxylic acid group both groups being derivable from the corresponding aromatic carbocyclic anhydride by reaction with hydrogen peroxide, said aromatic carboxylic compound optionally being further substituted by at least one of the groups selected from alkyl, carboxylate, sulphonate, nitro, chloro and bromo groups or Class (2)-a cycloaliphatic compound substituted around the cycloaliphatic nucleus by a carboxylate group and a peroxycarboxylic acid group both groups being derivable from the corresponding cycloaliphatic carbocyclic anhydride by reaction with hydrogen peroxide, said cycloaliphatic carboxylic compound optionally being further substituted by at least one of the groups selected from alkyl, carboxylate, sulphonate, nitro, chloro and bromo groups or Class (3)-an olefinically unsaturated aliphatic compound substituted by a carboxylate group and a peroxycarboxylic acid group, the carbonyl group of the carboxylate substituent being conjugated with the carbonyl group of the peroxycarboxylic acid via the olefinic unsaturation within the aliphatic compound, both substituents being derivable from the corresponding anhydride by reaction with the hydrogen peroxide and maintaining contact between the medium and the surface until at least some of the micro-organisms have been killed.

2. A process for sterilising/disinfecting in which the magnesium persalt in the sterilising medium provides an avox concentration of at least 200 ppm.

3. A process for sterilising/disinfecting in which the magnesium persalt present in the sterilising/disinfecting medium provides an avox concentration of from 400 to 2000 ppm.

4. A process for sterilising/disinfecting in which the sterilising fluid has a pH of from pH 5 to pH 7.

5. A process for sterilising/disinfecting in which the sterilising medium is buffered to within the pH range of pH 5 to pld 57.

6. A process for sterilising/disinfecting in which the sterilising fluid contains additionally one or more cationic surfactants.

7. A process for sterilising/disinfecting according to any preceding claim in which the sterilising fluid is employed within 24 hours after dissolution of the magnesium persalt in the medium.

8. A process according to any preceding claim in which the medium comprises at least 10% w/w of a C1-C4 aliphatic alcohol.

9. A process according to claim 8 in which the alcohol is present in a weight ratio to the magnesium persalt of from 10:1 to 100:1.

10. A process according to claim 8 or 9 in which the alcohol is ethanol, propanol or isopropanol or a mixture thereof.

11. A solid composition for dissolution to obtain a sterilising medium containing as active ingredient a magnesium persalt according to claim 1 comprising the magnesium persalt and one or more of the following in parts per weight each per part of the magnesium persalt:-- anionic surfactant, cationic surfactant, builder, bulking agent and optionally one or more sesquestrant, peracid stabiliser or redox indicator.

1 2. A process or composition according to any preceding claim in which the persalt is magnesium monoperoxyphthalate.

13. A process or composition for sterilising/disinfecting employing a magnesium persalt according to claim 1 and one or more novel features described herein either alone or in combination with any other feature described herein.

14. A process for sterilising/disinfecting substantially as described herein with respect to any one of the Example runs.