INTERACTIONS OF COSMETIC PIGMENTS WITH PRESERVATIVES 93 Table VI Bactericidal Activities of Methyl p-Anisate and MP Against Staphylococcus aereus Viable cell count after 5-hr incubation CH30 -O- COOCH3 Methyl p-anisate 1.60 x 108 HO -• COOCH 3 MP Below 103 The reaction system consisted of 0.2% methyl p-anisate or MP, respectively, plus 0.5 ml inoculum, and was shaken and incubated at 37øC for 5 hr. Aliquots were then decimally diluted with a 1% sterile solution of polysorbate 80. The number of surviving bacteria was determined by the viable cell count method. ment with ultramarine blue. From these observations, a possible structural change of MP caused by incubation with the pigment is: HO 0 COOCH3 ) xo•O COOCH3 It is presumed that there are two possible bondings: one is ionic bonding and the other is non-ionic or covalent bonding. If the phenolic hydrogen is substituted by a methyl radical, the bactericidal activity was greatly lowered as compared with the unsubsti- tuted MP (Table VI). The results indicate that the existence of the phenolic hydrogen is most important for the bactericidal activity of MP. 150 J I B7.5 WA VENdMSFR$ 0 Figure 9. IR spectrum of MP that was recovered after incubation without ultramarine blue.

94 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 150 o • ?s 11•.5 SH ISF•IOO F t'- IP ,l t I I I I •VENUM•ER$ Figure 10. IR spectrum of MP that was recovered after incubation with ultramarine blue. IR SPECTRA OF RECOVERED MP Figure 9 shows the IR spectrum of MP that was recovered after incubation without pigment. Figure 10 shows the IR spectrum of the MP that was recovered after incuba- tion with ultramarine blue. Since both IR spectra are similar, the possibility of covalent bonding due to interaction with pigment was rejected. CONCENTRATIONS OF METAL IONS Using inductively coupled plasma emission spectrometry, measurement of the concen- trations of various metal ions found in incubation mixtures was done (Table VII). The Table VII Concentrations of the Metal Ions Found in the Incubated Mixtures (ppm) From From From MP supernatant supernatant solution of A of B Zn 0.02 0.02 0.05 Fe 0.03 0.03 0.15 Mg 0.04 0.05 0.20 Si ND 3.7 3.5 A1 ND 0.38 0.07 Na 5 11 45 Ca 0.16 0.20 1.5 A: ultramarine blue dispersion. B: ultramarine blue q- MP dispersion. ND: not detectable.