AN IMPEDIMETRIC METHOD FOR RAPID SCREENING OF COSMETIC PRESERVATIVES

An efficient impedance method was developed for rapid evaluation of co smetic preservatives. The method used decimal reduction time or D-valu e to assess preservative efficacies, The D-value, which was calculated from the plot of Log CFU ml(-1) versus time by linear regression anal ysis, could be obtained within 48 h. Thus, the time required for the c hallenge test was reduced from 4-8 weeks with the standard procedures (eg US Pharmacopeia), to 2 days with the current method, A calibration curve (r = -0.95) was established by plotting the Log CFU ml(-1) vers us capacitance detection time (DT) of 108 samples, With the calibratio n, CFU can be estimated directly from the impedance test without plati ng. Two commercial biocides and several other chemicals were evaluated in a shampoo by the impedance procedure against Pseudomonas aeruginos a, The D-values obtained from the impedance test were not significantl y different from those produced by the conventional plate count method . The technique was found to be particularly useful when screening a l arge number of compounds to find novel preservatives and synergistic p reservative combinations.