we have discovered that dhaa is stable in solutions of pure polyol solvents and in solutions wherein the polyol content is greater than about 50 percent . by “ stable ” is meant that dhaa in these solutions deteriorates very slowly over a sufficient period of time that it can be stored and sold as a dietary supplement or as a skin care product , or as a concentrate for preparing or manufacturing them , with a reasonable shelf life . the solutions are made by oxidizing ascorbic acid that is first dissolved in a pure polyol solvent , or in water , or in some mixture of these liquids . the polyol concentration may be adjusted to about 50 % or greater prior to oxidizing the aa or afterwards . the solutions can also be made by oxidizing aa that is dissolved in an alcohol ( e . g ., ethanol ), and then combining the dhaa - containing alcohol with a polyol solvent . if it is desired that the final solution does not contain alcohol , the alcohol can be removed by evaporating the alcohol from the polyol solvent solution using heat or vacuum , or both . the solutions can also be made by dissolving solid dhaa in a pure polyol solvent , or in water , or in some mixture of these liquids . the polyol concentration may be adjusted to about 50 % or greater prior to dissolving the dhaa or afterwards . the organic polyol solvents are chosen for pharmaceutical and dietary acceptability , their ability to solubilize the aa and dhaa component , water content , and effect on the stability of the dhaa component . at present we prefer to employ commercially available glycerol which generally contains 5 % or less water . in general , we prefer to minimize the water content of the solvent ( s ), consistent with economic and functional considerations . other polyols which can be employed include propylene glycol , hexylene glycol , butylene glycol and the almost infinite molecular weight range of polyethylene glycols , as well as so - called sugar alcohols , e . g ., sorbitol and xylitol , and mixtures thereof with other polyols . these solutions can be prepared entirely with one polyol solvent , e . g ., glycerol , or mixtures of polyol solvents . the final choice of solvent will depend on economics and other relevant factors . methods we have successfully applied for oxidizing the ascorbic acid include the use of halogen or ozone or oxygen / activated charcoal or fenton &# 39 ; s reagent or ascorbic acid oxidase enzyme . all of these methods are known in the art , as are other methods ; the previously cited references pecherer and koliou show typical applications of various methods for example . the method by which the oxidation is accomplished is not the determinant factor of the long term stability of the dhaa in the solution , and other methods of oxidation are within the scope of the invention . aa concentration in solution is commonly measured as the reducing activity of the solution using starch - iodine titration methods that are well - known in the art . aa is also measured by ultra - violet spectrophotometry using a wavelength at which aa absorbs strongly and dhaa does not , typically about 265 nm . this method is also well known in the art . dhaa in solution can be converted into aa by reducing agents such as dithiothreitol ( dtt ) or tris ( 2 - carboxyethyl ) phosphine ( tcep ), and its concentration is commonly measured spectrophotometrically as the difference in absorbance of a solution subjected to reduction by dtt or tcep versus a similar solution that is not subjected to a reducing agent . these methods are also well - known in the art , but see deutsch for examples . in the description , claims , and the following examples , dhaa in the compositions of the invention is the vitamin c that can be measured by the difference in absorbance at 262 nm using tcep reducing agent . in a preferred embodiment of the invention , aa dissolved in glycerol and / or water is oxidized using ozone to produce dhaa solutions . water - based solutions and glycerol - based solutions may be combined to yield stable dhaa compositions having the desired polyol concentration . a 15 % aa solution in water was prepared by adding 15 grams aa per 100 ml purified water with stirring . a 15 % solution of aa in glycerol was prepared by adding 15 grams aa per 100 ml pure usp glycerol and stirring with heat . a corona - discharge type ozone generator with feed - gas of pure oxygen was used to supply an oxidizing gas containing about 5 % ozone , and each of the 15 % aa solutions was subjected to oxidizing conditions by bubbling the oxidizing gas through the solution using a glass diffuser . the progress of aa oxidation in each solution was monitored by the disappearance of reducing activity as measured by starch - iodine titration . each solution was subjected to the oxidizing conditions until all (& gt ; 99 %) of the original reducing activity had disappeared . the solution made with pure glycerol was labeled “ 100 % glycerol ,” and the solution made with purified water was labeled “ 100 % water .” portions of these two solutions were combined to produce solutions of various glycerol concentrations by weight , specifically “ 99 % glycerol ,” “ 98 % glycerol ,” “ 97 % glycerol ,” “ 96 % glycerol ,” “ 95 % glycerol ”, “ 90 % glycerol ,” and “ 50 % glycerol .” for example , 99 parts by weight of “ 100 % glycerol ” was combined with 1 part by weight “ 100 % water ” to produce the “ 99 % glycerol ” solution . aliquots of each of the solutions prepared above were placed in translucent , screw - capped polyethylene vials and were stored at room temperature . no attempt was made to further protect the vials from ambient indoor light , and each vial contained a headspace of normal air . each vial was periodically opened to remove a sample for stability testing over the next 229 days . the concentration of dhaa in each sample was measured by spectrometry on each testing day . the initial dhaa concentration of each solution on day 1 was recorded and assigned a value of 100 %, and the concentration on each subsequent stability test day was calculated as the percent remaining of the initial concentration . fig1 through 8 show the results of stability testing of the various glycerol - containing solutions ; each graph also shows the result of the “ 100 % water ” solution for comparison . it can be seen that dhaa decomposes rapidly in water . by the time the water solution was tested at 20 days , less than 10 percent of the initial amount of dhaa remained . by contrast , dhaa is preserved very well in solutions containing high concentrations of glycerol . in pure glycerol for example , greater than 80 % of the initial dhaa concentration remains even after approximately 8 months of storage at room temperature . as the glycerol concentration is reduced , stability is reduced , until only minor improvement is gained at 50 % glycerol concentration . in another embodiment , a stable dhaa composition is produced by oxidation of aa dissolved in glycerol using exposure to activated charcoal and oxygen as the oxidation method . a solution of aa in pure usp glycerol was subjected to oxidizing conditions by suspending activated charcoal in the solution and then bubbling pure oxygen through the solution . oxidation of aa during this process was monitored by starch - iodine titration . after the desired amount of aa had been oxidized , the activated charcoal was removed from the solution by centrifugation and filtration . this solution was labeled “ 100 % glycerol .” a portion of the solution was then placed in a translucent , screw - capped polyethylene vial and was stored at room temperature . no attempt was made to further protect the vial from ambient indoor light , and the vial contained a headspace of normal air . the vial was periodically opened to remove a sample for stability testing over the next 191 days . the concentration of dhaa in the sample was measured by spectrometry on each testing day . the initial dhaa concentration of the solution on day 1 was recorded and assigned a value of 100 %, and the concentration on each subsequent stability test day was calculated as the percent remaining of the initial concentration . fig9 shows the results of the stability testing of this solution , and for comparison also shows the stability of a dhaa solution prepared in purified water ( labeled “ 100 % water ”). it can be seen that dhaa in glycerol produced by an alternative oxidation method shows excellent long - term stability . in another embodiment , stable dhaa compositions are produced by oxidizing aa dissolved in water using fenton &# 39 ; s reagent as the oxidizing method , and then combining the water solution with propylene glycol such that the final concentration of polyol is 50 % or greater . aa was dissolved in purified water to give a highly concentrated solution , and then sufficient 30 % hydrogen peroxide was added to oxidize about half of the aa . iron to catalyze the reaction was provided by addition of ferrous sulfate . oxidation of the aa was monitored by spectrometry until the expected amount of aa had been oxidized . this solution was labeled “ 100 % water .” portions of this solution were combined with portions of pure , usp grade propylene glycol to produce solutions of “ 97 % propylene glycol ,” “ 95 % propylene glycol ,” “ 90 % propylene glycol ,” “ 80 % propylene glycol ,” “ 70 % propylene glycol ,” and “ 50 % propylene glycol .” for example , 3 parts by volume of the “ 100 % water ” solution were combined with 97 parts by volume propylene glycol to yield the “ 97 % propylene glycol ” solution . aliquots of each of the solutions prepared above were placed in translucent , screw - capped polyethylene vials and were stored at room temperature . no attempt was made to further protect the vials from ambient indoor light , and each vial contained a headspace of normal air . each vial was periodically opened to remove a sample for stability testing over the next 31 days . the concentration of dhaa in each sample was measured by spectrometry on each testing day . the initial dhaa concentration of each solution was recorded and assigned a value of 100 % ( day 0 ), and the concentration on each subsequent stability test day was calculated as the percent remaining of the initial concentration . fig1 through 15 show the results of stability testing of the various propylene glycol - containing solutions ; each graph also shows the result of the “ 100 % water ” solution for comparison . it can be seen that dhaa decomposes rapidly in water ; after only 5 days , less than 20 percent of the initial amount of dhaa remains . by contrast , dhaa is preserved very well in solutions containing high concentrations of propylene glycol . in fact , the dhaa concentration in many of these solutions actually increased significantly over time , a remarkable and unexpected discovery . we believe this phenomenon can be explained this way : residual aa continues to oxidize while the dhaa is stabilized and therefore accumulates in the solution . the spectrophotometric measurements support this explanation , but we do not wish to be bound by this explanation . example 3 demonstrates that stable dhaa compositions may be prepared using a third alternative oxidation method as compared with the first two examples , and also demonstrates that an alternative polyol solvent can be used . while the above description contains many specificities , these should not be construed as limitations on the scope of the invention , but rather as exemplification of preferred embodiments . the compositions can be prepared using various methods and ingredients as mentioned , and their equivalents . polyol solvents are known to be antimicrobial in high concentrations and therefore the compositions of the invention generally do not require preservatives . polyol solvents are also capable of dissolving substances that are not soluble in water , so are capable of solubilizing not only aa and dhaa but additional dietary or skin - enhancing ingredients such as vitamin e . many polyol solvents are excellent skin - enhancing substances in their own right , such as glycerol which is commonly utilized in skin care products as a humectant . many polyol solvents are not only safe for ingestion , but in fact have a pleasant , sweet flavor . thus the compositions have favorable properties that are synergistic with their use as dietary supplements , skin - enhancers , concentrates , or research solutions . accordingly , the scope of the invention should be determined not by the embodiments illustrated , but by the appended claims and their equivalents .
stable liquid compositions containing the oxidized form of vitamin c known as dehydroascorbic acid are provided . the compositions comprise dehydroascorbic acid and a pharmacologically acceptable liquid organic polyol solvent for said dehydroascorbic acid , wherein said polyol solvent comprises about 50 % or greater of the total weight of said composition . the compositions are useful as dietary supplements , skin - enhancers , concentrates , or research solutions .