100 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 4. Polyphosphates do not combine readily with all of multivalent metallic ions. On the other hand, the polyphosphates have the obvious advantage of cheapness and bulk which recommends them for such products as bath salts. But EDTA is effective at extreme dilutions and this is the condition needed in cosmetics. EDTA chelates are stable not only in extreme dilutions but they are stable also in hot acids or bases for indefinite periods of time even in extreme dilutions. EDTA forms stable complexes with all the di- and trivalent metals. Complexes are also stable under all conditions encoun- tered by cosmetics, such as pH range, manufacture and storage, and use. The EDTA complexes are more stable than those of the phosphates since the degree of ionization is nil or exceedingly small. The textile industry has accepted EDTA and its salts with open arms. I want to discuss some of these applications, especially, because of the points of similarity between wool, human hair, and even skin. All are chelating agents for metals by virtue of their amino acid building blocks. In the processing of textiles, the mill may soften water by zeolite softeners. But since wool and cotton both contain calcium, magnesium, and iron, placed there by nature and also due to soil, it is necessary to add something else to the processing waters to act as a scavenger for these trace contaminants. The characteristics of the EDTA salts make them perfect for this scaveng- ing action. Otherwise, these metal ions form insoluble soaps with the scrub- bing soaps or by reaction with fatty soil present if detergents only are used in cleaning. These insoluble hard water soaps interfere with the evenness of dyeing and other processing. Calcium, magnesium, and especially iron, cause serious interference in the dye bath resulting in varying shades of dyeing and uneven dyeing. When using a product like EDTA one of the first questions to arise is: How much will be required? In most cases this can be calculated stoichiometrically. However, in some acid solutions as much as two or three times of the theoretical is required. Also, in chelating iron in strongly alkaline solutions, an amount beyond the theoretical is re- quired. Since these EDTA salts are so very stable, it is not necessary to add an additional quantity to make up for possible decomposition or break- down on standing. On the other hand, it is desirable to add enough EDTA to ensure chelation of the maximum amount of trace metal ions which can be expected to occur. As an example, the molecular weight of calcium car- bonate is 100 while that of ethylene diamine tetraacetic acid is 292. This means that approximately 3 gm of ethylene diamine tetraacetic acid, or of its salt on the EDTA basis, will completely chelate 1 gin. of calcium cal- culated as calcium carbonate. There is one application very close to the cosmetic field. This is the use of a fraction of a per cent of EDTA salt in soap bar stock. The soap. manufacturer will frequently call this an antioxidant. Actually, it is not

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