Marking system and method for use in decontamination procedures

Abstract

A method of marking a residual aqueous contaminant on a surface 20 to be decontaminated comprises mixing a first part 11 of a marking system comprising a pH-sensitive dyestuff with first pH and first

Description

FIELD OF THE INVENTION The present invention relates to a marking system and to a method of marking a surface, in particular the surface of a medical device, to identify the presence and position of residual aqueous contaminants on the surface. BACKGROUND TO THE INVENTION Within the healthcare market, decontamination procedures are widely used for disinfection and cleaning. Areas of particular importance include the reprocessing of medical devices, such as example surgical instruments, ultrasound probes, endoscopes and the like. For infection control and patient safety, it is essential that any process used for decontamination or disinfection is effective in practice, taking into account the products used for disinfection, the training and performance of the user, environmental factors, and so on. Existing methods for reprocessing such medical devices typically include multiple process steps. For example, a first step may be performed in which the device is cleaned with a cleaning agent, for the removal of gross contaminants (such as ultrasound gel) and soiling from the surface. In a second step, disinfection or sterilization may takes place using chemical, thermal, or radiative means. In a third step, a rinsing process may be performed to remove left over chemical residue, particularly where the disinfection step uses a chemical disinfectant. One example of a three-step decontamination system, in which a chlorine dioxide-based disinfecting agent is used, is described in WO 2005 / 107823 A1. Many other disinfectant compositions are also used in the art, including those based on chlorine, peracetic acid, hydrogen peroxide, hypochlorite, quaternary ammonium compounds, tertiary amines and so on. Disinfection may also be achieved for example by exposure to UV radiation, steam or heat. When a pre-disinfection cleaning step is required, failure to adequately clean the device prior to disinfection has the potential to markedly increase the risk of cross-contamination and post-procedure infection. By failing to remove contaminants such 5 as ultrasound gel before disinfection, the performance of the disinfectant can be impaired. For example, the disinfectant may react with the remaining contaminants, reducing the efficacy of the disinfectant on the surface. Also, the contaminants may shield or cover areas of the surface, preventing them from being properly exposed to the disinfecting agent. 10 Against that background, it would be desirable to provide methods and systems to allow the presence and position of contaminants on a surface to be disinfected to be readily determined. SUMMARY OF THE INVENTION Aspects of the invention are specified in the independent claims. Preferred features are specified in the dependent claims. A first aspect of the invention provides a method of marking a residual aqueous contaminant on a surface to be decontaminated, the method comprising: - (a) mixing a first part of a marking system with a second part of the marking system, wherein the first part of the marking system comprises a pH-sensitive dyestuff and has a first pH, and exhibits a first colour, and the second part of the marking system comprises a pH modifier, and wherein, upon mixing the first and second parts of the marking system, a marker composition is obtained that has a second pH and exhibits a second colour, different to the first colour; and - (b) applying the marker composition to the surface, such that the marker composition changes colour from the second colour to a third colour, different to the second colour, when in contact with a residual aqueous contaminant on the surface having a pH that differs from the second pH, thereby marking the position of said contaminant with the third colour. Advantageously, the first part of the marking system can have a pH that optimises the stability of the pH-sensitive dyestuff. After mixing with the second part, a marker composition is produced that has a pH at which the dyestuff exhibits a visually different, second colour. Upon exposure to a residual aqueous contaminant with a different pH, the dyestuff changes colour to another, third colour (which may be the same as or similar to the first colour). The pH of the marker composition can be optimised for visibility of the colour change upon contact with the contaminant. The marker composition pH may not be optimal for the stability of the dyestuff, but because the marker composition can be produced at the point of use, this reduced stability is acceptable. ln one example, the residual aqueous contaminant has a pH of between 5 and 7, preferably between 5.5 and 6.5. The residual aqueous contaminant may for example comprise an ultrasound gel. The method may comprise dispensing the first and second parts of the marking system from a container having a first chamber for the first part, a second chamber for the second part, and a dispenser operable to dispense together a quantity of the first part and a quantity of the second part. The first and second parts of the marking system may be dispensed from such a container, or otherwise, onto an applicator, in particular a wipe. The step of mixing the first and second parts may occur on the applicator, and the method may include using the applicator to apply the marker composition to the surface. In a second aspect, the invention extends to a method of decontaminating a surface, comprising performing the method of the first aspect to mark the position of residual aqueous contaminants on the surface, and removing the contaminants from the surface. Removing the contaminants from the surface may be performed by manual wiping. The manual wiping may be performed by an applicator for the marker composition. The method of decontaminating the surface may comprise confirming that the contaminants have been removed from the surface by verifying that the third colour is no longer present. The method of decontaminating the surface may further comprise applying a disinfecting agent to the surface. Preferably, the disinfecting agent causes the marking agent to change from the second colour to colourless or to a fourth colour. The disinfecting agent may for example comprise chlorine dioxide. In a third aspect, the invention provides a marking system for use in the method of the first or second aspects. The marking system comprises a first part comprising a pH-sensitive dyestuff, the first part having a first pH and exhibiting a first colour, and a second part comprising a pH modifier. The first part and the second part can be mixed with one another to obtain a marker composition, where the marker composition has a third pH and exhibits a second colour, different to the first colour. The dyestuff may comprise a compound selected from the group comprising anthocyanins, anthocyanidins, betanins, and mixtures thereof. Preferably, the dyestuff is an anthocyanin. In one embodiment, the dyestuff comprises red radish dye. In one embodiment, the first pH is between 2 and 4, and the second pH is between 9 and 12, more preferably between 9.8 and 11.5. The second part may comprise sodium carbonate or another suitable base as the pH modifier. The first and / or second parts of the marking system may comprise a viscosity modifying agent a sequestering agent and / or a chelating agent. The marking system may further comprise an applicator, in particular a wipe. The marking system may comprise a container having a first chamber for the first part, a second chamber for the second part, and a dispenser operable to dispense together a quantity of the first part and a quantity of the second part. In the context of this application, the term “colour change” may refer to any colour change that is visually discernible by a user with regular vision. Examples of such colour changes include those where the wavelength of the observed colour changes by at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm or at least 60 nm, and those in which the change is from a perceived colour to colourless or vice versa. Preferred and / or optional features of each aspect and embodiment of the invention may also be used, alone or in appropriate combination, in the other aspects and embodiments also. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which like reference signs are used for like features, and in which: Figure 1 is schematic illustration of steps in a method of decontaminating a surface; and Figure 2 is a flowchart of the method shown in Figure 1. DESCRIPTION OF THE PREFERRED EMBODIMENTS In this specification, unless the context demands otherwise, the amount of a component in a composition is expressed as wt% (wt / wt% or weight / weight). This corresponds to the mass of each component relative to the total mass of the composition, expressed as a percentage. The present invention relates to using a pH-sensitive marker composition which exhibits a colour change in presence of certain contaminants on a surface to be decontaminated, for example on the surface of a medical device. When prepared, the marker composition exhibits a distinctive marking colour. If the surface is free from residual aqueous contaminants, then the marker composition will retain the marking colour when applied to the surface and the surface will exhibit a uniform colour in all areas. However, if aqueous contaminants are present on the surface, such as remnants of ultrasound gel, then when applied to the surface the pH of the marker composition will be shifted towards the pH of the contaminant. The local pH change of the marker composition causes a local colour change, revealing locations where the contaminant is present. The surface can then be subjected to further cleaning to remove all residual contamination before the surface is disinfected. Preferably, the marking colour of the marker composition changes (for example to become colourless) upon exposure to the disinfectant used in the disinfection process, so that the marker composition not only reveals the presence of contaminants before disinfection, but also allows the user to verify that the subsequent disinfection process has been applied to all areas of the surface. While pH-sensitive dyestuffs (i.e. dyestuffs that exhibit a change of colour upon a change in pH) are well-known in the art, the present inventors have determined that many such dyestuffs are most stable - and therefore most conveniently provided as a commercial product - at a pH that does not differ sufficiently from the typical pH of contaminants of interest to produce a distinctive colour change upon exposure to the contaminants. For example, most natural pH-sensitive dyestuffs are stable at acidic pH values, and most ultrasound gels are also acidic. Conversely, if a dyestuff is provided in a composition with a pH that is selected so that exposure to a contaminant of interest produces a pH change that results in a significant, readily observable colour change, the dyestuff is sufficiently unstable that the shelf-life of the starting composition is too short to be commercially acceptable. Embodiments of the present invention address those problems by providing a marking system having a first part in which a pH-sensitive dyestuff is carried in a composition having a pH at which the dyestuff is sufficiently stable to give the composition a commercially useful shelf life (e.g. of a year or more), and a second part containing a pH modifier. The first part, which initially exhibits a first colour, can be mixed with the second part at the point of use to provide a marker composition. The resulting marker composition has a different pH to the first part, and therefore exhibits a second colour as a result of the pH-sensitive dyestuff changing colour in response to the change in pH. The marker composition then exhibits a significant colour change upon exposure to residual aqueous contaminants that have a different pH to the pH of the marker composition, allowing the location of the contaminant on the surface to be revealed. The stability of the dyestuff in the marker composition may be considerably reduced compared to the stability of the dyestuff in the first part of the system but, because the marker composition is produced in-situ at the point of use, this reduced stability is of no consequence. Preferably, the first and second parts of the marking system are dispensed onto an applicator, in particular a wipe, and can be mixed on the wipe before the wipe is used to apply the resulting marker composition to the surface. A method of marking a residual aqueous contaminant on a surface to be decontaminated using a marking system according to the invention will now be described with reference to Figures 1 and 2. In this example, the marker composition is applied to a surface of a medical device using a wipe. As shown in Figure 1 (a), the marking system 10 comprises a first part or composition 11 and a second part or composition 12, together with an applicator wipe 14. In this example, the first and second parts 11, 12 are aqueous compositions that are contained in separate chambers of a dual-chamber container 16. The container is fitted with a pump dispenser head 18 that is operable to dispense a quantity of the first part 11 and a quantity of the second part 12 simultaneously, optionally as foams. Preferably, the first and second parts 11,12 are only brought into contact with one another once dispensed onto the applicator. The first part 11 is provided as an aqueous solution including a pH-sensitive surface marker that comprises a dyestuff. The dyestuff is sensitive to changes in pH, resulting in a corresponding colour change upon a change in pH. The first part 11 has a first pH and exhibits a first colour. For the purposes of illustration, in this example, the dyestuff is a red radish extract, the first pH is between 2 and 4, and the first colour is red. The second part 12 of the marking system is an aqueous solution that has a second pH that differs from the first pH. In this example, the second part 12 comprises a base, such as sodium carbonate, and the second pH is from about 10 to 12. The second part 12 in this example is colourless. In step 101 (Figure 2) of the method, the first and second parts 11,12 are dispensed from the container 16 onto the wipe 14, as shown in Figure 1 (a). The wipe 14 is then folded and scrunched to mix the first and second parts 11,12 (step 102) and form the marker composition 15, which in this example has a pH from about 9 to 10.5, and the colour changes from the initial red colour of the first part 11 to blue-purple of the marker composition 15 after mixing. The user can determine that sufficient mixing has taken place once the colour change is complete, and once the marker composition 15 appears to be a uniform colour on the applicator wipe 14 (Figure 1(b), step 103 in Figure 2). Then, the wipe 14 is used to apply the marker composition 15 to the surface of the device 20 (Figure 1(c), step 104 in Figure 2). It is desirable that the whole of the surface to be decontaminated is covered by a uniform, continuous coating of the marker composition 15. Residual aqueous contaminants, such as ultrasound gel, may be present on the surface of the device 20 at the time of application of the marker composition 15. Although efforts are usually made to remove such contaminants by manual wiping, rinsing, or by the use of pre-disinfection wipes, some residual contamination may remain. In such cases, the marker composition 15 mixes with the contaminant, which results in a change of pH of the marker composition 15 only in the areas in which the contaminant is present. Ultrasound gel, for example, typically has a pH of between 5.5 and 6.5, which is lower that the marker composition pH (in this example) of between about 9 and 10.5. Accordingly, exposure of the marker composition 15 to ultrasound gel results in a reduction of pH of the marker composition 15. This pH change causes a corresponding colour change to the dyestuff and therefore to the marker composition 15, which will exhibit a third colour, different to the second colour, where the contaminant is present. In the present example, the presence ultrasound gel at a pH of around 5.5 to 6.5 will result in the marker composition turning from blue-purple (the second colour) to pink or red (the third colour) in the regions of contamination. As shown in Figure 1(d), the presence and position of such contaminants on the surface of the device 20 will therefore be observed by the user as regions 22 of different colour (step 105 in Figure 2), and can provide an indication that further cleaning is required to remove the contaminant from the surface. To remove the contaminant, the user may continue to wipe the surface with the wipe 14 (Figure 1(e), step 106 in Figure 2). This continued wiping manually removes the contaminant by transferring it to the wipe 14, and re-applies the marker composition 15 to the surface; once the marker composition 15 no longer changes to the third colour on the surface, it can be concluded that the contaminant has been sufficiently removed. Wiping continues until the surface appears with a uniform coating of the second colour (Figure 1(f)). If no pH-modifying contaminants are present on the surface of the device 20 at the time of application of the marker composition 15, no colour change to the third colour will be observed, and the surface will be uniformly coloured with the colour of the marker composition (i.e. the second colour) without further cleaning. In that case, step 106 in Figure 2 can be omitted. The device 20 is then subjected to a disinfecting step (step 107 in Figure 2). In such cases, a suitable disinfecting agent, such as chlorine dioxide, may be applied to the surface of the device 20 with a suitable applicator. In this example, a two-part chlorine dioxide disinfectant system is shown, in which first and second parts of the disinfectant system are contained in a two-chamber container 30 and dispensed as foams onto a wipe 32, where they are mixed to produce a chlorine dioxide disinfectant 34 in-situ on the wipe (Figure 1(g)). The wipe 32 is then used to apply the disinfectant 34 to the device 20 (Figure 1(h)). A suitable chlorine dioxide disinfectant system is described in European Patent No. 1843765 B1. The dyestuff of the marker composition, in this example, undergoes a colour change in the presence of chlorine dioxide, from coloured to colourless. This further colour change allows the user to visually validate that the areas marked by the marker composition 15 have changed colour, and therefore that these areas have been exposed to chlorine dioxide during the disinfection process. After successful disinfection, no residual colour can be seen on the device 20 (Figure 1(i)). Log entries may be made at each step of the above method such that an audit trail is produced, for regulatory, training, or monitoring purposes. For example, a log entry may be made once the marker composition is applied to the surface of the device, with the outcome recorded in the log. Outcomes may include whether a uniform colour was provided on the surface, or whether and where the colour change to the third colour was observed, indicative of the presence of pH-modifying contaminants. A subsequent log entry may be made once further wiping of the surface has occurred to provide a uniform colour on the surface, corresponding to removal of the pH-modifying contaminant from the surface, and the subsequent disinfecting steps may also be logged. Further details of the marking system and its constituents will now be described. The first part of the marking system comprises a pH-sensitive dyestuff (i.e. a dyestuff that exhibits a colour change when in solution when the pH of the solution is changed). The dyestuff is most preferably a natural dyestuff that is soluble or substantially soluble in water. Examples of suitable dyestuffs may include anthocyanins, anthocyanidins, betanins, phycocyanins, and carotenes (in particular beta-carotenes). Anthocyanin dyestuffs have been found to be particularly suitable. Table 1 shows a range of tested anthocyanin dyestuffs, and records the first colour exhibited by the dyestuff when in the first part of the marking system (i.e. a composition with a pH range of 2 to 4, in which the dyestuffs exhibit long-term stability), and the second colour exhibited in the marker composition (i.e. after mixing with the second part having a pH of between 9.8 and 11.5). The pH of the resulting marker composition is also recorded. All of the dyestuffs exhibited a visible colour change to a third colour upon exposure to ultrasound gel at a pH of 5.5 to 6.5. It was found that all of the dyestuffs were oxidised by chlorine dioxide when in the 5 marker composition, inducing a colour change from the marker composition to colourless. Table 1 Dye Start (first) colour in first part (pH 2 to 4) Marker (second) colour after mixing with second part pH of marker composition Oxidised with CIO2? NatPure XFINE Red Radish Red Blue-purple 9.0-10.0 Yes NatPure XFINE Potato Pink Turquoise 9.5-10.5 Yes Blue Pea Blue-purple Green 9.5-10.5 Yes Natural RD31 Pink-dark red Blue-green 9.0-10.0 Yes NatPure Colfine Plum Red Blue 9.0-10.0 Yes E163 Durant Pink-red Blue-green 9.5-10.5 Yes NatPure XFINE Beetroot BR312 Pink Purple-pink 9.5-10.5 Yes 10 Other tested dyestuffs included spirulina (phycocyanin), which was blue in the first part at a pH of 2 to 4 and blue-green in the marker composition at a pH of 9.5 to 10.5, and Natpure col Red LC313 (beta-carotene), which was pink in the first part at a pH of 2 to 4 and blue-purple in the marker composition at a pH of 9.5 to 10.5. In a preferred embodiment, the dyestuff is a red radish dye, commercially available for example as NatPure XFINE Red Radish. The first part of the marking system may comprise from 1 wt% to 20 wt% of the dyestuff. Preferably, the first part of the marking system comprises from 1 wt% to 15 wt%, 1 wt% to 10 wt%, 1 wt% to 8 wt%, or 1 wt% to 5 wt% of the dyestuff. The pH of the first part of the marking system is selected to optimise the stability of the dyestuff and therefore the shelf life of the first part of the marking system. For the dyestuffs mentioned above an optimum pH is from 2 to 4. It was found that an acidic solution afforded greater dyestuff stability with a reduced rate of degradation of the dyestuff in solution. It has been observed for example that the red radish dyestuff retains its stability in the first part of the marking system without significant degradation for at least 16 weeks at 40°C at a pH of from 2 to 4. It will be appreciated that different dyestuffs may exhibit optimum stability at different pH ranges. The second part of the marking system comprises a pH modifier in aqueous solution. In the case where the first part of the marking system is acidic, the pH modifier is a base. Preferably, for use with a first part as described above, the second part has a pH of from 9 to 12, or from 9.5 to 12, or most preferably from 9.8 to 11.5. Any suitable water-soluble base may be used as the pH modifier. Preferably, the base is sodium carbonate. In other embodiments, alternative bases may be suitable, such as other metal carbonates such as potassium carbonate, or metal hydroxides such as sodium hydroxide. The second part of the marking system may comprise from 1 wt% to 10 wt% of the pH modifier. Preferably, the second part of the marking system comprises a total of from 1 wt% to 8 wt%, from 1 wt% to 7 wt%, from 1 wt% to 6 wt%, from 2 wt% to 8 wt%, from 2 wt% to 7 wt%, from 2 wt% to 6 wt%, from 3 wt% to 8 wt%, from 3 wt% to 7 wt%, or from 3 wt% to 6 wt%, of the pH modifier. In their simplest forms, the first and second parts of the marking system may comprise simple aqueous solutions. Thus the first part may comprise the pH-sensitive dyestuff with a simple acid, such as citric acid, to bring the pH to the target range; and the second part may be an aqueous solution of the pH modifier. Preferably, however, the first and second parts of the marking system may each comprise one or more further components that enhance the performance of the resulting marker composition in terms of its ability to wet the surface and form a uniform layer, as well as its drying behaviour once spread onto the surface, colour enhancement, stability, foaming and other factors. It is preferred that the first and second parts have the same or a similar base composition (i.e. the components other than the dyestuff for the first part, and other than the pH modifier for the second part). This can make dispensing and mixing of the first and second parts easier. To that end, in one example, the first and / or second parts of the marking system comprise a water-soluble organic solvent. It is desirable that the solvent has low toxicity, has a high flash point (to reduce flammability), is biodegradable and has a suitable evaporation rate to allow for spreading and even drying of the marker composition after application to the surface. Simple solvents such as ethanol and isopropyl alcohol are therefore not preferred for one or more of these reasons. Suitable tested solvents include propanediol. More generally, the solvent may be a diol, particularly an isoprene diol or branched-chain dialcohol, or a ketal. The first and / or second part of the marking system may comprise from 1 wt% to 5 wt% of the organic solvent. Preferably, the first and / or second part of the marking system comprises from 1 wt% to 4 wt% of the organic solvent, more preferably from 1.5 wt% to 3.5 wt% of the organic solvent. Each of the first and / or second parts of the marking system may comprise a surfactant. The surfactant contributes to the ability of the marker composition to wet the surface of the medical device or the work surface. Good wetting ability is important, since medical device surfaces are often designed to resist wetting (i.e. they may have hydrophobic properties and a smooth texture). It was found that an alcohol ethoxylate propylate, Berol (Registered Trade Mark of Nouryon) 185, and a decyl glucoside, SugaDet D (Registered Trade Mark of Colonial Chemical), were suitable surfactants. In some examples, the first and / or second parts of the marking system may include a UV filter, such as Surfacare (Registered Trade Mark of Surfachem) PCE 567. In some examples, the first and / or second parts of the marking system may include an odour absorber, such as ColaQuat (Registered Trade Mark of Colonial Chemical) SME. The first and / or second part of the marking system may comprise a total of from 1 wt% to 10 wt% of surfactant. Preferably, the first and / or second part of the marking system comprises a total of from 1 wt% to 8 wt%, from 1 wt% to 7 wt%, from 1 wt% to 6 wt%, from 2 wt% to 8 wt%, from 2 wt% to 7 wt%, from 2 wt% to 6 wt%, from 3 wt% to 8 wt%, from 3 wt% to 7 wt%, or from 3 wt% to 6 wt%, of surfactant. The first and / or second parts of the marking system may comprise a viscosity modifying agent. The viscosity modifying agent is provided to thicken the composition for improved spreadability on the surface of the medical device. Suitable tested viscosity modifying agents include xanthan gum, hydroxyethyl cellulose, nonionic guar gums, and polyacrylates. The first and / or second part of the marking system may comprise from 0.01 wt% to 3 wt% of the viscosity modifying agent. Preferably, the first and / or second part of the marking system comprises from 0.1 wt% to 1 wt% of viscosity modifying agent. It is preferred that the second part has a lower viscosity than the first part, particularly when the first part is dispensed as a foam, so that the second part mixes readily with the first part. To this end, the first part may comprise more viscosity modifying agent than the second part. In one embodiment, the second part comprises 50% or less of the viscosity modifying agent than the first part. The first and / or second parts of the marking system may include a sequestering agent or chelating agent. When present, a sequestering agent can chelate impurities, in particular heavy metals, which might otherwise cause degradation of protein-based pigments. A sequestering agent may therefore improve the shelf-life of the marking system and increase tolerance to impurities introduced during manufacturing or in use. Suitable sequestering agents include tetrasodium glutamate diacetate (an aminopolycarboxylate-based chelating agent), available as Dissolvine (Registered Trade Mark of Nouryon) GL38 (Glutamic acid, N,N-diacetic acid, tetrasodium salt), trisodium ethylenediamine disuccinate, disodium EDTA and tetrasodium EDTA. The first and / or second part of the marking system may comprise from 0.01 wt% to 5 wt% of sequestering agent. Preferably, the first and / or second part of the marking system comprises from 0.1 wt% to 1 wt% of sequestering agent. The first and / or second parts of the marking system may include a preservative, such as parmetol (Registered Trade Mark of Vink Chemicals) BPX. The first and / or second part of the marking system may include up to 2 wt%, and preferably from 0.1 wt% to 1.5 wt % of preservative. The first / and or second part of the marking system may include a fragrance additive, such as a citrus fragrance. The first and / or second part of the marking may comprise up to 1 wt%, or up to 0.5 wt% of fragrance additive. Table 2 shows the composition of the first and second parts of a marking system in accordance with a preferred embodiment of the invention. Table 2 Composition of first part of marking system wt% Composition of second part of marking system wt% RO Water 86.225 RO Water 88.9 Zemea Propranediol 2.5 Zemea Propanediol 2.5 Xanthan Gum 0.25 Xanthan Gum 0.1 Dissolvine GL38 0.25 Dissolvine GL38 0.25 Sodium Chloride PDV 2 Sodium Carbonate 2.5 Surfacare PCE 567 0.075 Berol 185 3 ColaQuat SME 1 Suga Det D 1.75 Suga Det D 2.75 Parmetol BPX 1 Berol 185 1.75 Parmetol BPX 1 Red Radish Dye 1.6 Citrus Fragrance 0.25 Citric Acid 0.35 5 The marking system may also include a suitable applicator for applying the marker composition to the surface. The applicator is preferably a wipe, comprising a woven or non-woven fabric of natural or synthetic material, but may be a sponge, a swab, a mop or any other suitable apparatus. When an applicator is provided, the first and second parts may be dispensed onto the applicator (for example as foams, gels, 10 liquids or any combination of these), and mixed on the applicator. It is also possible for the marker composition to be produced otherwise than on an applicator, for example by mixing the two parts of the marking system in a mixing container. For example, the first and second parts may be dispensed into a spray 15 bottle and mixed, and then sprayed onto the surface. In another example, the first and second parts may be dispensed into and mixed in a tray, and then applied to the surface by dipping the device in the tray. The first and second parts of the marking system may be provided in any suitable containers. However, as shown in Figure 1, it is particularly advantageous to provide the first and second parts in a container having two chambers and equipped to dispense the two parts simultaneously as a foam. A suitable container is described for example in European Patent No. 1843765 B1. It would also be possible to provide the first and second parts in separate containers, to provide sachets of one or both parts, or to provide a wipe or other applicator pre-impregnated with one of the parts, so that the other part can be dispensed onto the applicator. The method and marking system described herein can be applied to substantially any surface to be decontaminated. It is particularly useful where the surface is the surface of a medical device, for example an invasive or non-invasive ultrasound probe, an endoscope, nasendoscope, transvaginal probe, or any other similar device. The surface to be decontaminated may be substantially the whole surface of the medical device or only a part of the medical device. The method can also be applied to other surfaces, such as counter tops, room surfaces such as floors and walls, furniture and so on. The method and marking system described herein can be used to reveal the presence and position of several different types of residual aqueous contaminant, provided the contaminant has a pH that differs sufficiently from the pH of the marker composition to induce a colour change in the dyestuff. The contaminants can therefore be described as pH-modifying contaminants (i.e. contaminants which result in a pH change of the marker composition, where the pH change is sufficient to result in a pH change-induced colour change of the dyestuff). While the systems described in detail here are particularly suitable for the detection of mildly acidic ultrasound gels with typical pHs of 5.5 to 6.5, it will be understood that other contaminants with a similar pH can also be detected. With suitable choices for the dyestuff and the pH of the marker composition, a marking system according to the invention could be adapted to reveal contaminants with different pH values, with the significant advantage that, by forming the marker composition by mixing the first and second parts, the pH of the marker composition can be substantially different to the pH at which the dyestuff is most stable. The disinfection step described above could be substituted for other disinfection processes, for example by using a different disinfectant composition such as chlorine, chlorine dioxide, peracetic acid, hydrogen peroxide, hypochlorite and so 5 on. In further examples, disinfection may be performed using UV light or high temperature (in which cases the marker composition may lose colour due to UV or thermal degradation of the dyestuff). Further modifications and variations not explicitly described above can also be 10 contemplated without departing from the scope of the invention as defined in the appended claims.

Claims

1. A method of marking a residual aqueous contaminant on a surface to be decontaminated, the method comprising:- (a) mixing a first part of a marking system with a second part of the marking system,wherein the first part of the marking system comprises a pH-sensitive dyestuff and has a first pH, and exhibits a first colour, and the second part of the marking system comprises a pH modifier, and wherein, upon mixing the first and second parts of the marking system, a marker composition is obtained that has a second pH and exhibits a second colour, different to the first colour;and- (b) applying the marker composition to the surface,such that the marker composition changes colour from the second colour to a third colour, different to the second colour, when in contact with a residual aqueous contaminant on the surface having a pH that differs from the second pH, thereby marking the position of said contaminant with the third colour.

2. The method of Claim 1, wherein the residual aqueous contaminant has a pH of between 5 and 7, preferably between 5.5 and 6.5.

3. The method of Claim 1 or Claim 2, wherein the residual aqueous contaminant comprises an ultrasound gel.

4. The method of any of Claims 1 to 3, comprising dispensing the first and second parts of the marking system from a container having a first chamber for the first part, a second chamber for the second part, and a dispenser operable to dispense together a quantity of the first part and a quantity of the second part.

5. The method of any of Claims 1 to 4, comprising dispensing the first and second parts of the marking system onto an applicator, in particular a wipe, wherein mixing the first and second parts occurs on the applicator, and using the applicator to apply the marker composition to the surface.

6. A method of decontaminating a surface, comprising- performing the method of any one of Claims 1 to 5 to mark the position of residual aqueous contaminants on the surface; and- removing said contaminants from the surface.

7. The method of Claim 6, comprising removing said contaminants from the surface by manual wiping.

8. The method of Claim 7, wherein the manual wiping is performed by an applicator for the marker composition.

9. The method of any of Claims 6 to 8, comprising confirming that the contaminants have been removed from the surface by verifying that the third colour is no longer present.

10. The method of any of Claims 6 to 9, further comprising applying a disinfecting agent to the surface, wherein the disinfecting agent causes the marking agent to change from the second colour to colourless or to a fourth colour.

11. The method of Claim 10, wherein the disinfecting agent comprises chlorine dioxide.

12. A marking system for use in the method of any of Claims 1 to 5, comprising: a first part comprising a pH-sensitive dyestuff, the first part having a first pH and exhibiting a first colour;a second part comprising a pH modifier;wherein the first part and the second part can be mixed with one another toobtain a marker composition, the marker composition having a second pH and exhibiting a second colour, different to the first colour.

13. The marking system of Claim 12, wherein the dyestuff comprises a compound selected from the group comprising anthocyanins, anthocyanidins, betanins, and mixtures thereof.

14. The marking system of Claim 13, wherein the dyestuff comprises red radish dye.

15. The marking system of any of Claims 12 to 14, wherein the first pH is between 2 and 4, and the second pH is between 9 and 12, more preferably between 9.8 and 11.5.

16. The marking system of any of Claims 12 to 15, wherein the second part comprises sodium carbonate as the pH modifier.

17. The marking system of any of Claims 12 to 16, wherein the first and / or second parts comprise a viscosity modifying agent.

18. The marking system of any of Claims 12 to 17, wherein the first and / or second parts comprise a sequestering agent and / or a chelating agent.

19. The marking system of any of Claims 12 to 18, further comprising an applicator, in particular a wipe.

20. The marking system of any of Claims 12 to 19, further comprising a container having a first chamber for the first part, a second chamber for the second part, and a dispenser operable to dispense together a quantity of the first part and a quantity of the second part.s

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