RADIOISOTOPES IN DETERGENT AND COSMETIC RESEARCH 369 Figure 8. DETERGENT RESEARCH In respect to soaps and detergents as a class of compounds, primary use of radioisotopes has been in reference to "detergent evaluation" or deter- mination of the detergent's ability to remove soil from specific substrates. In usual studies employed to evaluate detergents the procedures used are somewhat lengthy, require bulky equipment and results obtained are dependent on a fairly close control of experimental techniques. In some instances with certain substrates, evaluation is very difficult. Therefore a considerable number of articles have been published in an attempt to find more suitable methods for detergent evaluation. Methods using, radioisotopes have been reported and appear to be excellent. Studies have been undertaken by several investigators to determine the efficiency of detergents in removing oily soils from metal surfaces (17, 18, 19, 20, 21). In these studies, carbon-14 tagged compounds such as fatty acids and their derivatives have been used. By use of carbon-14 tagged stearic acid as the oily soil, the properties of several metal cleaning solutions have been investigated (18, 19). The effect of sequestrants on detergent action has also been studied in respect to the removal of dirt containing fission products as tagging agents, especially for evaluation of detergency in respect to radiological decontamination (21). Other ex- periments have involved the synthesis of radioactive bacteria by feeding the bacterial cultures radioactive phosphorus 32, in order to study the ability of various detergents to remove bacteria from dishes and utensils associated with the preparation and serving of food (22, 23). The studies of primary interest to manufacturers of soaps and detergents have been those which have developed techniques whereby "detergent

330 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS evaluation" may be undertaken routinely in respect to removal of soil from textile fibers. In this respect extensive studies have been undertaken into the preparation of radioactive soil that would truly be representative of the usual soil found on cloth (24, 25). Among the radioactive materials used as tagging agents for soil have been fission products, carbon-14 and calci- um-45. One complete technique in use by several companies for detergent evaluation utilizes an oily paste prepared from radioactive carbon-14 lampblack mixed with mineral oil as the soiling agent (26). In the test, cloth is •i'oiled by first picking up a small amount of the oily soil on an etched plate and then mechanically rubbing traces of the soil onto Indianhead muslin swatches. The swatches are radioassayed to obtain the amount of radioactivity representative of the amount of initial soiling present, and are then washed in a miniaturized "washing apparatus" with the detergent to be tested. The swatches are dried and again radioassayed and the amount of soil remaining is thus determined. Soil redeposition in the pres- ence of the test detergent may be studied by including an unsoiled swatch in the washing apparatus and determining the amount of radioactivity picked up by this swatch. The commercial availability (27) of cloth swatches soiled with carbon-14 tagged lampblack, protein or fat has further simplified the technique. This test method is simpler, reasonably inexpensive, more sensitive and faster than usual evalua'tion studies utilizing reflectometers or visual in- spection as an index of cleaning ability. Furthermore, changes in the surface of the cloth which can cause changes in reflectance have no effect in the radiotracer technique. An additional advantage is that because of the small quantities of all substances used, very small amounts of detergent may be evaluated. Further improvement of the technique has recently been made with the preparation of a radioactive clay as a soiling agent (28). This clay is prepared by the addition of calcium-45 or strontium-90 salts to normal clay with subsequent isotope exchange and the formation of "tagged" clay. Determination of quantitative adsorption of tagged soaps and detergents onto textile fibers has also been undertaken. The adsorption of sulfur-35 tagged sodium lauryl sulfate and sodium alkyl benzene sulfonates arid carbon-14 tagged sodium palmirate has been studied. These studies were undertaken not only to correlate detergent action and soil removal prop- erties with adsorption, but also to study the effect of detergent adsorption on soil redeposition. Other uses are known for radiotracers in the detergent and cosmetic field. The complete theology of systems involving the addition of one component to another have been studied. By use of iodine-131 or sodium- 22, the addition of "builders" and additives to detergent bases has been