CHELATING AND SEQUESTERING AGENTS IN COSMETICS 10! an antioxidant but, more properly, a stabilizer, since the EDTA complexes the traces of iron, copper, and other metals which get into the soap during the manufacturing process and then these metallic contaminants cannot act as oxidation catalysts. Another application in the cosmetic field is the use of EDTA in liquid soap shampoos. These can be manufactured and filtered so that they are clear and have a high polish. However, after bottling in glass bottles and standing for some weeks, they may become cloudy due to the extraction of calcium from the glass and the resultant formation of insoluble calcium soap. The use of as little as one-tenth of one per cent of EDTA salt in these shampoos will generally supply protection against this type of unsightly development. Many people feel that soap still makes the best shampoo as compared to synthetic detergents. They feel that it is less harsh on the hair. A su- perior soap product can be made for use with at least moderately hard water by the incorporation of larger quantities of EDTA salts. These salts can also be effectively used in synthetic shampoos to prevent the formation of any insoluble calcium soap which may form from any fatty soil almost certain to be present. EDTA also prevents iron stains on light colored hair when used either in a synthetic shampoo or in a soap shampoo. Un- tortunately, most water is likely to pick up iron from the water pipes and since hair is a chelating agent, it tends to stain the hair. This gives a mud- dying effect just as with dye in textile dyeing. The blonds and the red- heads, especially, object to this. Incidentally, EDTA does have some de- tergent properties of its own. I believe one of the most desirable applica- tions of EDTA is in a rinse to follow shampooing. This rinse might well be made from the trisodium salt of EDTA which has a pH of 8.5 an emollient may also be incorporated. This rinse containing EDTA has, far stronger chelating properties with the resulting ability to remove the last trace of insoluble soap and iron or metal stain than do any of the lemon type of rinses. Traces of iron and copper are well known to be bad actors when present in organic materials containing double bonds, ketone, and aromatic struc- tures. These certainly characterize perfumes. When small amounts of EDTA are used in perfumes, colognes, and similar products, color develop- ment and odor modification is greatly retarded. Creams and lotions generally contain soap or fatty acid bases and other fatty materials. These fatty materials can be stabilized with ethylene- diannine tetraacetic acid just as bar soap may be. EDTA will also pro- tect perfume and color. There is one interesting consideration regard- ing lotions. They usually contain a rather small per cent of solids and a very much smaller quantity of emulsifier. During their shelf life the glass container releases calcium ions which react to form calcium soap. This

102 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS may use up much of the small amount of emulsifier present and, worse yet, convert it to a product which is insoluble and water repellent. This can seriously affect the stability of the emulsion or even break it. There is one other interesting effect, in creams and lotions, of the EDTA salts. Studies have shown that they sequester and chelate the nutrient minerals which are required for the growth of bacteria and micro6rgan- isms so that these mie'roSrganisms in'many cases literally starwe'and can- not continue growth. For this reason they have a definite preserving, effect. It is well known that iron darkens deodorant and an•iperspirant creams with their acid pH. One pays a premium for iron-free raw materials such as aluminum trichloride. The EDTA salts are especially active in chelating iron under these acid conditions. Their use to scavenge the last traces of iron which may cause you trouble is therefore of compelling interest. The purest commercial form of EDTA is 99 per cent pure and is actually running closer to 99• with the other half per cent mostly water and sodium sulfate. The product is an odorless and colorless powder. Also available are the di-, tri-, and tetrasodium salts which are frequently more convenient to use than is the acid. In distilled water, the acid has a solubility of about 0.02 per cent. This doesn't seem like very much but it is 200 parts per million and that is frequently enough to more than tie up the traces of iron and copper which may be present in a product. The solubility increases as you go from the mono- to the di-, to the tri-, and to the tetrasodium salt. We understand, of course, that in many cases sodium salts in your product are not desirable and in those cases it is relatively easy to use the free EDTA and make the salt of any metal or amine desired. Finally, I would like to mention some other interesting applications of these sal•s which are not related to the cosmetic field. In Florida, for years they have had trouble with iron chlorosis which is due to a shortage of available iron in the soil. They can add all of the common iron salts they want to the soil and the tree is still not able to assimilate it. How- ever, the addition of only a few ounces of the iron salt of ethylenediamine tetraacetic acid will show up in improvement within a few days. We do not understand the mechanism whereby the tree is able to extract the iron from the complex nor do we know whether or not the iron complex itself is first absorbed and then the iron removed or whether the absorp- tion is of the iron only. It has been found that many soils actually con- tain iron but that it is unavailable to the plants. The addition of EDTA or of its sodium salt to these soils will chelate iron present and make it available to plants. There has been considerable additional work upon cotton and corn and this work indicates that these complexes will be economically useful for these crops, too. Some work has been done with