46 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS MONO ALKYL PHOSPHATE MONO SODIUM SALT ,OH C N H2N+i0-P =0 {]-NA + N=I2 KRAFT POINT: 31,5 oe M C : 3,5 x I0 -3 MOLE/L MINIMUM SURFACE TENSION 27.5 DYNE/CM ALKYL SULFATE SODIUM SALT o C N H2N+i =0 {5-NA + N=I2 C M C : 7,2 x I0 -3 MOLE/L MINIMUM SURFACE TENSION 32,0 DYNE/CM Figure 1. Surface active properties of monolauryl phosphate mono-sodium salt and lauryl and sulfate sodium salt. 300 200 • 100 Figure 2. Foam height-concentration curve of monoalkyl phosphate monosdium salts measured by the Ross and Miles method.

SKIN IRRITATION BY ANIONIC SURFACTANTS 47 300 --200 .. •1oo I •4 1 3 3 1 •2 I •1 I C o,nc. (mole/ I ) Figure 3. Foam height-concentration curve of alkyl phosphates with several alkyl and salt types in comparison with C•2AS. C12mono-salt: CuMAP mono-sodium salt Cusesqui-salt: CuMAP sesqui-sodium salt Cudi-salt: CuMAP di-sodium salt sesqui-alkyl: sesqui-Cualkyl phosphate. its surface active properties, MAP monosodium salts, except C•6MAP, reveal a foaming power equal to alkyl sulfate, with the highest power in CuMAP. There are three major type of salts in MAP, namely mono-, sesqui- and di-salts, and their foam properties are shown in Figure 3. It can be seen that the mono- and sesqui-salts possess a good foaming power similar to that of CuAS, whereas the foam produced by the di-salt or the sesqui-alkyl derivative is relatively unstable and low in its foam height. Weight % IOO AOS •so m --LAS 0 0.5 1.0 3.0 C0nc. (%) uv% lOO[ •*•AOS 0 0.5 1.0 3.0 Conc. (%) Figure 4. Defatting potency of various common anionic surfactants shown by a decrease in both oil weight and absorbance of Sudan Black dye after washing for 10 min at 37øC. AS: sodium dodecyl sulfate, LAS: linear alkyl benzene sulfonate, AOS: alfo-olefin sulfonate, ES: dodecyl ether sulfate.