78 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (8:2) and the other with chloroform-methanol (9:1). Each plate was allowed to develop until the solvent front migrated about 10 cm, then the plates were air-dried. The preservative was located as described below in Visualization of Preservatives. Final Identification-The sample solution was spotted along with the stan- dards of preservatives with similar B/s on a new plate and developed as described above for preliminary screening. Visualization of Preservatives The following steps were taken to locate and identify the preservative: The tlc plate was examined with a short wavelength UV light. A reddish- brown spot will indicate the presence of a UV-absorbing material which may Table II Rr Values and Results • with Indicator Reagents _ Rt Detection by Preservative C6H•-Acetone CHCI•-MeOH UV I_o Indicator Reagents b (8:2) (9:1) Bronopol 0.47 0.57 E, violet F, yellow Butylated hydroxytoluene 0.79 0.83 X B, yellow Carvacrol 0.65 0.75 X A, pink B, yellow Chlorhexidine acetate 0.40 0.62 X 4-Chloro-3-methyl phenol 0.59 0.65 X l•-Chloro-m-xylenol 0.60 0.67 X Dehydroacetic acid 0.15 0.26 X Dichloro-m-xylenol 0.65 0.75 X Dichlorophene 0.50 0.62 X X Fluorsalan 0.56 0.53 X A, pink B, yellow Germall 115 0.00 0.00 X C, pink E, violet F, yellow Itexachlorophene 0.14 0.41 X X A, pink B, yellow Irgasan CF• 0.53 0.67 X Irgasan DP 300 0.74 0.81 X MDM hydantoin 0.23 0.59 Octyl gallate 0.12 0.22 X X o-Phenyll0henol 0.68 0.79 X X Propylparaben 0.56 0.65 X X Resorcinol 0.39 0.34 X X Salicylanilide 0.65 0.72 X X Tetrabromo-o-cresol 0.72 0.80 X Tribromsalan 0.60 0.69 X Trichlocarban 0.55 0.70 X Vantide 89 RE 0.70 0.83 Zinc pyrithione 0.49 '0.82 X X E, violet F, yellow A, pink B, yellow A, green B, yellow C, pink "Only positive tests are indicated. 0 A, B, C, etc., refer to indicator reagents used.

IDENTIFICATION OF PRESERVATIVES 79 be the preservative. The spots should be outlined with a spatula for future location. A tank containing a few crystals of iodine was warmed and the fie plate was placed into the 1.2 vapors. Formation of brown spots will indicate the presence of organic compounds. The spots should be outlined for future location, as the iodine will gradually disappear. The same fie plate and/or additional plates was sprayed evenly with suggested spray reagents. Additional plates must be developed if more than one spray reagent is used, as the reagents form stable chemical derivatives. Rs's for the located spots were calculated as follows: distance of spot center from start point Ill = distance of solvent front from start point Results were then compared with standards to identify the preservative. PtESULTS AND DIscussioN A total of 26 perservatives were examined by the described procedure, with the results shown in Table II. All preservatives except dimethoxane were de- tectable by one or more of the visualization procedures. The Rf values given Table III Results of Adding Preservatives to a Commercial Shampoo Rr Preservative Standard Shampoo Detected by Butylated hydroxytoluene 0.85 0.86 I,, Carvacrol 0.67 0.66 I,_, p-Chloro-m-xylenol 0.59 0.58 I,_, Chlorhexidine acetate 0.59 0.60 I,_, 4-Chloro-3-methyl phenol 0.60 0.61 I,, Dehydroacetic acid 0.26 0.26 UV Dichloro-m-xylenol 0.70 0.72 I,_. Dichlorophene 0.53 0.55 UV, I_o Fluorsalan 0.54 0.57 UV Gcrmall 115 0.00 0.00 I, Reagent C Hexachlorophene 0.35 0.33 UV, Irga,'an CF:• 0.64 0.65 UV Irgasan DP 300 0.68 0.68 UV o-Phenylphenol 0.76 0.75 UV, Propylparaben 0.55 0.56 UV, I2 Resorcino] 0.24 0.26 UV, Salicylani]ide 0.73 0.74 UV, T• trabromo-o-creso] 0.64 0.65 UV, very faint Tribromsalan 0.60 0.60 UV Trichlocarban 0.66 0.66 UV Vancide 89 RE 0.81 0.81 Reagent C Zinc pyrithione 0.78 0.76 UV, Is