86 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ppt /./[ Cosmetic pigment l : .erwV:',ieVr e Incubate for 5 hr at 37øC Centrifugation I Supernatant Determinate the preservative by HPLC technique. Figure 1. Method of determining the adsorbed preservative. IR MEASUREMENTS The infrared spectra of the recovered MP (Figure 2) were measured in KBr disks using a FT-IR (Gigilabo Co.). MEASUREMENT OF THE CONCENTRATIONS OF METAL IONS Measurements of the concentrations of various metal ions found in the recovered MP (Figure 2) were performed with an inductively coupled plasma emission spectrometer JY-48P (Jobin Yvon Co.). /•/tultramarine blue MP dist. water • keep for 5 hr centrifugation I • 1 supernatant ppt free•ze-dried redissolve in (CDa)aCO determine •H-NMR and •aC-NMR Figure 2. Method of measurement of •H and 13C-NMR spectra. at 37øC

INTERACTIONS OF COSMETIC PIGMENTS WITH PRESERVATIVES 87 PREPARATION OF Na AND K SALTS OF P-HYDROXYBENZOIC ACID ESTERS A column (1.5 cm X 30 cm) was packed with a slurry of ion-exchange resin (Amberlyst XN-1004) in CH3OH and washed with a large quantity of methanolic NaC1 or KC1. p-Hydroxybenzoic acid ester was placed on the column and eluted with methanol. Elutate was concentrated by evaporation. Whether or not the replacement of phenolic hydrogen with Na or K was complete was determined by •H-NMR spectroscopy. RESULTS AND DISCUSSION DETERMINATION OF THE BACTERICIDAL ACTIVITIES OF THE PRESERVATIVES IN THE PRESENCE OF COSMETIC PIGMENTS Figure 3 shows IDs for various pigments using S. aureus. The bactericidal activity of MP was significantly inhibited in the presence of all pigments except kaolinite and silica alumina, whereas the bactericidal activity of BP was not significantly inactivated by any of the pigments tested. The degree of inactivating activity against MP, EP, and PP was highest for ultramarine blue followed by talc, titanium dioxide (R), titanium dioxide (A), red oxide of iron, and yellow oxide of iron, in decreasing order. Red oxide of iron Yellow oxide of iron Titanium dioxide (A) Titanium dioxide (R) Talc Ultramarine blue Silica alumina Kaolinite • against MP v///, against EP -• against PP ß .• against BP i i 10 -s 10 -a 10 -• I.D. Figure 3. Effects of pigments on the bactericidal activity of p-hydroxybenzoic acid esters against Staphylo- coccus aureus.