Abstract:
Stable aqueous glycerin iodine concentrates are provided which are adapted for dilution in water to yield germicidal iodine use solutions. The concentrates include from about 30-87% by weight glycerin, from about 0.15-15% by weight iodine, from about 0.15-15% by weight iodide ion, and one or more additives such as compatible wetting agents, hydrotropes, thickening agents, additional emollients and buffering systems. The concentrates are stable for a period of at least about 3 months at room temperature and are dilutable at a ratio of 1 part concentrate with from about 2-80 parts water. The concentrates can be formulated to give very low free iodine values as concentrates, but provide dramatically increased free iodine values as diluted use solutions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with aqueous stable glycerin iodine concentrate products which can be diluted with water to form germicidal use solutions. More particularly, the invention pertains to such concentrates which have a high content of glycerin above 30% by weight, iodine, iodide ion and additive(s) (e.g., surfactants, hydrotropes, thickening agents, additional emollients, and/or buffering systems) which upon dilution yield high quality germicidal solutions with elevated free iodine values. 
     2. Description of the Prior Art 
     Iodine solutions have been used as germicidal agents for many years. In order to create useful solutions of this type, it is necessary to solubilize the iodine therein. Different solubilization approaches have been used in the past. These include hot processes wherein iodine is reacted with ethylene glycol or nonionic surfactants so that the resulting mixture is soluble in water, and room temperature solubilization using polyoxyethylene nonionic surfactants, polyvinylpyrrolidone or iodide ion. All of these solubilizing agents form a complex with the iodine, which in turn yields solutions (generally referred to as iodophores) which are used without further dilution and have varying concentrations of free or uncomplexed iodine (I 2 ). Free iodine is a critical factor in determining the germicidal effectiveness of such iodine solutions, and therefore control of the free iodine level is very desirable if not essential. 
     It is known that the stability of aqueous iodine use solutions may depend upon the level of free iodine therein. However, high concentrations of free iodine corresponds to high levels of iodine vapor. In open containers, the iodine vapor will eventually cause a depletion of iodine from the solution. In plastic containers the iodine tends to dissolve into and eventually penetrate the container. Given that use solutions with a high free iodine value are generally more effective germicides, it would therefore be desirable to formulate a product having a low free iodine value during storage but which at the time of use could be adjusted to have a high free iodine value. 
     Many use solution iodophores designed for topical application are formulated with emollient in order to provide a soothing, skin-protective effect. In addition, most emollients will complex with free iodine thus assisting in adjustment and control of the free iodine content of the iodophore. The most common emollient used in such cases is glycerin, and may be present at a level of from about 1-15% by weight in products such as teat dips. Glycerine iodine use formulations also normally include one or more additives which are necessary to give the final use solutions desired physical properties. For example, surfactants are often used to provide wetting properties to insure complete contact between the surface to be disinfected and the use solution. Hydrotropes are also used to aid in the addition of other ingredients and to insure stability of the use solution. Buffering systems and thickening agents are also sometimes employed. 
     In recent years, manufacturers have sought to develop germicidal concentrate products which can be diluted with water at the point of use. Concentrates reduce manufacturing and freight costs, save storage space and minimize problem of disposing of containers. While certain types of iodophores can be readily formulated as dilutable concentrates, a significant problem arises when the concentrates contain appreciable amounts of glycerin and attendant additives such as surfactants, hydrotropes, additional emollients, buffering systems and thickeners. Specifically, high glycerin content iodophore concentrates tend to be unstable and rapidly separate into phases. This means that the end user must thoroughly mix the concentrate before dilution thereof. Such a requirement is not only inconvenient for the user, but can lead to use solutions having widely varying free iodine contents owing to inadequate mixing of the separated concentrate. As can be appreciated, if a given use solution has too high a free iodine content, it may be irritating; on the other hand, if the use solution has an inadequate free iodine content, its germicidal properties may be compromised. 
     To give but one example, a number of surfactants which are quite useful in the formulation of glycerin iodine diluted use solutions are incompatible when employed in the formulation of corresponding concentrates. Thus, polyoxyethylene alcohols, polyoxyethylene nonylphenol, polyalkylene block copolymers and polyvinylpyrrolidone are very difficult to use in concentrate formulations having high glycerin contents. 
     There is accordingly a need in the art for high glycerin content/low free iodine value iodophore concentrate products which have significant stability over long periods of storage, and which can be readily diluted with water to form use solutions having high, predictable and controlled free iodine contents. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems outlined above, and provides greatly improved stable aqueous glycerin iodine concentrates adapted for dilution in water to yield use solutions. The concentrates of the invention are aqueous solutions including from about 0.15-15% by weight iodine, from about 0.15-15% by weight iodide ion derived from alkali metal iodide or hydriodic acid, and from about 30-87% by weight glycerin. The concentrates further include one or more additives for giving the final diluted use solutions desired physical properties. Such additives are selected from the group consisting of up to about 10% by weight of a compatible wetting agent, up to about 10% by weight of a compatible hydrotrope, up to about 2% by weight of a compatible thickening agent, up to about 30% by weight of an emollient different from glycerin, a sufficient amount of a buffering system to maintain the pH of the diluted use solutions at a level of from about 3-9, and mixtures of any of the foregoing. Generally, the concentrates of the invention are dilutable in water at a ratio of one part concentrate with from about 2-80 parts water (1+2 to 1+80 concentrate+water dilutions) to give the use solutions; more preferably, the dilution ratio is 1 part concentrate with from about 3-30 parts water. 
     As used herein, &#34;free iodine&#34; is the concentration of I 2  which is not complexed with other species such as iodide ions I 3 . A certain concentration of free iodine I 2  is always present in iodine solutions because of equilibrium reactions such as 
     
         I.sub.3.sup.- ⃡I.sub.2 +I.sup.- 
    
     or in general 
     I 2  (complexing agent) ⃡I 2  +complexing agent. Free iodine is preferably determined by the method of Winicov et al., Proc. Int. Symposium on Povidone, University of Kentucky College of Pharmacy, pp. 186-92 (1983), incorporated by reference herein. 
     The concentrates of the invention should be stable for a period of at least about three months at room temperature (i.e., about 25° C.) storage, more preferably for a period of at least about six months, and most preferably for a period of at least about one year. As used herein with reference to the concentrates, &#34;stable&#34; means that the concentrates remain as substantially single phase, homogeneous solutions throughout a given storage period at room temperature and at least 90% of the starting iodine concentration remains. &#34;Compatible&#34; concentrate ingredients are those which permit initial mixing of all of the ingredients of the concentrate to form the substantially single phase, homogeneous solutions, and which in combination provide the desirable concentrate stability. 
     The compatible wetting agents most useful in formulating concentrates of the inventions include sulfonates such as the alkyl sulfonates, aryl sulfonates, alkyl aryl sulfonates, alkyl diphenyloxide disulfonate, dialkyl sodium sulfosuccinates, sulfonated amphoterics such as alkylamphohydroxy propyl sulfonate, polysulfonates such as lignosulfate, C 8  -C 16  alkyl polyglycosides, sodium alcohol sulfates, and mixtures thereof. Compatible hydrotropes advantageously include sulfonates such as octane sulfonate, napthlene sulfonate, and mixtures thereof. 
     Thickening agents can be selected from the group consisting of cellulose derivatives such as hydroxy ethylcellulose and carboxy methylcellulose, sodium alginate, xantham gum and mixtures thereof. The non-glycerin emollients useful in the invention are generally selected from the group consisting of sorbitol, the alkylene glycols (e.g., ethylene glycol and propylene glycol), the polyols, and mixtures thereof. Buffering systems are generally taken from the group consisting of an acid such as the mono-, di- and tri- C 2  -C 10  carboxylic acids (e.g., acetic acid, glycolic acid, oxalic acid and citric acid), inorganic acids such as phosphoric acid, and corresponding salts of the foregoing acids. 
     C 2  -C 10  fatty acids such as lactic acid can also be incorporated into the concentrates of the invention. Generally, these fatty acids form a part of the buffering system. It has been found that low molecular weight fatty acid such as lactic acid can be slowly oxidized by iodine at a concentrate pH above 5, and therefore the most stable concentrates contain no more than about 2% fatty acid at pH&gt;5. If the concentrate pH is 5 or below, the fatty acids are not oxidized as readily, and in such cases as much as 10% fatty acid can be added. 
     The concentrates hereof may be prepared in a number of ways. The preferred procedure involves combining the water and thickening agents and mixing until a uniform dispersion is obtained. The additional ingredients such as buffering systems, surfactants and hydrotropes are then added and agitated until all ingredients are completely dispersed. Finally, the glycerin, other emollients, iodine and alkali metal iodide are added with agitation to complete the concentrate. Iodine may be added in the form of a complex such as sodium iodide-iodine complex. The formulation process does not require any heat, and therefore the mixing procedure is generally carried out at room temperature. Gentle warming of the mixture or at least 80°-100° F. may facilitate preparation of the formulation, but is not required. 
     A characteristic of the concentrates of the invention is that as concentrates, they exhibit very low free iodine levels. However, upon dilution to form use solutions, the free iodine levels are significantly increased. Therefore, the concentrates exhibit very desirable storage properties without the deleterious effects of high free iodine values. At the same time, upon dilution the end products have the very necessary high free iodine levels for germicidal purposes. 
     The present invention thus permits preparation of germicidal iodine concentrates having controlled free iodine concentrations, both as concentrates and as use solutions. Accordingly, the concentrates may be formulated to meet the needs of a wide variety of end uses. For example, where a use solution may be exposed to significant amounts of blood, a relatively high concentration of available iodine is necessary because of the tendency of the iodine to react with blood components. On the other hand, where the use solutions are exposed for only a minimal organic load, lower concentrations of available iodine will give proper performance. 
     Many concentrates of the invention can be formulated with a complete absence of wetting agents and hydrotropes. These concentrates have excellent stability, but their corresponding use dilutions may have relatively poor physical properties because of the lack of the omitted wetting agents and hydrotropes. This is not a serious problem, but it will reduce the germicidal efficiency of the diluted product. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following examples 11-16 describe concentrates and diluted use solutions in accordance with the invention, whereas examples 1-4 describe comparative formulas containing non-ionic surfactants and examples 5-10 demonstrate the properties of several other glycerin-iodide compositions. It is to be understood that these examples are provided by way of illustration only, and nothing therein should be taken as a limitation upon the overall scope of the invention. 
     EXAMPLE 1 
     A typical type of 1% iodine, 10% glycerin germicidal use solution was prepared using 10 g of Igepal CO-720 (12 mole nonylphenol ethoxylate), 1.08 g iodine, 0.48 g sodium iodide, 10 g glycerin, 0.5 g citric acid, 0.39 g of 50% sodium hydroxide and sufficient water to give a total weight of 100 g. This mixture goes into solution after about 1 hr. of agitation and is relatively stable. 
     As a comparison, a concentrate formula was prepared wherein all of the ingredients were tripled. This mixture did not blend properly even after extensive mixing, and the concentrate separated into two layers after sitting overnight. This lack of storage stability is a significant and common problem encountered when attempting to formulate a concentrated germicidal solution containing significant amounts of glycerin. 
     EXAMPLE 2 
     In this example, a concentrate was prepared by dissolving 0.1 g Igepal CO-720 (12 mole nonylphenol ethoxylate) in 30 g water. Then 7.6 g of sodium iodide, 5.0 g iodine, 50 g glycerin and sufficient water to give a total weight of 100 g were added to the mixture. After 1 day a precipitate formed in the bottom of the container. As a comparison, the identical formulation was prepared except that the Igepal CO-720 was omitted. This gave a stable concentrate which did not form a precipitate. 
     EXAMPLE 3 
     In this example, a concentrate was prepared by dissolving 0.1 g Pluronic P105 (ethylene oxide-propylene oxide copolymer) in 30 g water. Then 7.6 g sodium iodide, 5.0 g iodine, 50 g glycerin and water to give a total weight of 100 g were added. After 1 day, a precipitate formed in the container. A comparative concentration formulation identical to the above was also prepared, except that the Pluronic P105 was omitted. This comparative concentrate was stable and did not yield a precipitate. 
     EXAMPLE 4 
     A concentrate was prepared by dissolving 0.1 g Kollidon 30 (PVP) in 30 g of water. Then 7.6 g sodium iodide, 5.0 g iodine, 50 g glycerin and sufficient water to give a total weight of 100 g were added. After 1 day, a precipitate formed. A companion concentrate prepared with these same ingredients, save for the omission of the Kollidon 30, was stable. 
     Examples 1-4 illustrate that the most common complexing agents used in iodine germicidal solutions create problems where high concentrations of glycerin are used, even when sufficient amounts of iodide are present which would normally tend to maintain the iodine fully solubilized. 
     EXAMPLE 5 
     Seventeen g of water were combined with 1.6 g sodium iodide, 1.2 g iodine and 80 g of glycerin. At 20° C., the free iodine content of this concentrate is 2.6 ppm iodine. However, a 1+7 aqueous dilution of the concentrate exhibited a 20° C. free iodine content of 95 ppm. 
     EXAMPLE 6 
     48.7 g of water were combined with 7.3 g sodium iodide, 4.0 g iodine and 40 g glycerin. The free iodine content of this concentrate formulation at 20° C. is 2.3 ppm. A 1+3 aqueous dilution of the concentrate exhibited a free iodine value of 74 ppm. 
     EXAMPLE 7 
     6.3 g of water were combined with 8.0 g of sodium iodide, 5.7 g iodine and 80 g of glycerin. The free iodine content of this concentrate at 20° C. is 1.4 ppm, whereas a 1+39 dilution had a free iodine value of 148 ppm. 
     Examples 5-7 illustrate the difference in free iodine level of concentrate solutions versus diluted use forms of the products. The free iodine of the diluted solutions is primarily determined by the ratio of the iodine:iodide concentration. The free iodine of the concentrate is determined mainly by the high concentration of glycerin therein. In comparison, Lugol&#39;s solution, which contains 5% iodine, 10% potassium iodide and no glycerin, has a free iodine content of 168 ppm. A 1+7 dilution of Lugol&#39;s solution has a free iodine content of 267 ppm. Therefore, for iodine/iodide solutions that are free of glycerin, the free iodine values of the concentrates and of the diluted use solutions are similar. 
     EXAMPLES 8-10 
     An iodine concentrate was prepared by combining 16.4 g water, 2.2 g sodium iodide, 0.2 g acetic acid, 1.2 g iodine and 80 g glycerin (Example 8). A similar concentrate was prepared by combining 16.2 g water, 2.2 g sodium iodide, 0.3 g sodium citrate, 0.1 g citric acid, 1.2 g iodine and 80 g glycerin (Example 9). A third concentrate was prepared by combining 16.2 g water, 2.2 g sodium iodide, 0.16 g acetic acid, 0.24 g sodium acetate, 1.2 g iodine and 80 g glycerin (Example 10). 
     The following table illustrates the stability of the Examples 8-10 concentrates thereof after three weeks storage at 50° C. and dilutions. These formulations show little loss of iodine. The pH of the diluted products is partly dependent on the pH of the water used for the dilution. The storage data demonstrates the stability of the concentrates. 
     
                       TABLE 1______________________________________              Exam-   Exam-Concentrate/Dilution - Property              ple 8   ple 9   Example 10______________________________________1 + 7 dilution with DI water - pH              4.1     5.2     5.0concentrate at 20° C. - free iodine              1.4 ppm 1.0 ppm 1.4 ppmvalue1 + 7 dilution with DI water at 20° C. -               63 ppm  67 ppm  68 ppmfree iodine valueconcentrate - initial percent iodine              1.17    1.15    1.17concentrate - percent iodine after 3              1.14    1.12    1.14weeks at 50° C.______________________________________ 
    
     EXAMPLE 11 
     A concentrate was prepared by combining 30 g glycerin, 3 g iodine, 4.6 g sodium iodide, 0.1 g acetic acid, 0.2 g sodium acetate, 0.3 g Glucopon 425 (alkyl polyglycoside), and sufficient water to give a total weight of 100 g. This concentrate can be diluted at 1+5 ratio to give a germicidal use solution containing 0.5% iodine and 5% glycerin. 
     EXAMPLE 12 
     A concentrate was prepared by combining 80 g glycerin, 0.57 g iodine, 0.81 g sodium iodide, 0.2 g acetic acid, 0.2 g sodium acetate, 0.35 g Aerosol OT (sodium dioctyl sulfosuccinate), and sufficient water to give a total weight of 100 g. The concentrate can be diluted at a 1+5 ratio to give a germicidal use solution containing 0.09% iodine and 13.3% glycerin. 
     EXAMPLE 13 
     A concentrate was prepared by combining 40 gm glycerin, 3.14 gm iodine, 4.57 gm sodium iodide, 1.13 gm of mono basic sodium phosphate monohydrate, 1 gm Mirataine CBS (cocamidopropyl hydroxysultaine), and sufficient water to give a total weight of 100 g. The concentrate can be diluted at 1+19 ratio to give a germicidal use solution containing 0.16% iodine and 2% glycerin. 
     EXAMPLE 14 
     A concentrate was prepared by combining 70 g glycerin, 3.5 g iodine, 5.26 g sodium iodide, 0.25 g lactic acid, 0.1 g sodium hydroxide, 0.35 g Aerosol OT (sodium dioctyl sulfosuccinate), 0.35% Keltrol, and sufficient water to give a total weight of 100 g. The concentrate can be diluted at a 1+6 ratio to produce a 0.5% iodine/10% glycerin use solution. 
     EXAMPLE 15 
     A concentrate was prepared by combining 40 g glycerin, 4.0 g iodine, 6.06 g sodium iodide, 0.2 g lactic acid, 0.15 g sodium hydroxide, 0.20 g Aerosol OT 75 (sodium dioctylsulfosuccinate), 0.20% Keltrol T (xanthan gum), and sufficient water to give a total weight of 100 g. The concentrate can be diluted at a 1+3 ratio to give a 1% iodine/10% glycerin use solution. 
     EXAMPLE 16 
     A concentrate was prepared by combining 50 g glycerin, 1.25 g iodine, 1.88 g sodium iodide, 0.1 g lactic acid, 0.1 g sodium hydroxide, 1.25 Miranol CS (cocoamphohydroxypropylsulfonate), 0.3% sodium alginate, and sufficient water to give a total weight of 100 g. The concentrate can be diluted at a 1+24 ratio to give a 0.05% iodine/2% glycerin use solution. 
     The following Table 2 sets forth approximate broad and preferred ranges for the concentrate ingredients of the invention, which are dispersed in water to make the final concentrates. 
     
                       TABLE 2______________________________________Concentrate Ingredients.sup.1             Broad Range                        Preferred Range______________________________________Glycerin          30-87      50-80Iodine            0.15-15    0.6-11.7Iodide ion from alkali metal iodide or             0.15-15    0.8-7.3hydriodic acidWetting Agent     up to 10%  0.2-4.0Hydrotrope        up to 10%  0.2-4.0Thickening Agent  up to 2%   0.1-0.5Emollient different than glycerin             up to 30%  0-30Fatty Acid Buffer.sup.2 at pH 5 or above             up to 2%   .2-.5Fatty Acid Buffer.sup.2 at pH below 5             up to 10%  .2-4Inorganic Buffer such as Phosphate             up to 10%  0.2-4Dilution Ratio    1 + 2 to 1 + 80                        1 + 3 to 1 + 30pH of Use Dilution             3-9        3-7______________________________________ .sup.1 All data given as percent by weight of aqueous concentrate unless otherwise indicated. .sup.2 pH values refer to pH of concentrate solutions.