DETERMINATION OF IMIDUREA 199 u 40 2o 1 2 3 4 t, - o • , • • io i2 i4 i• Minutes Figure 4. A: MEKC electropherogram of the separation of (1) imidurea, 0.693 mg/mL (2) methylparaben, 0.135 mg/mL (3) ethylparaben, 0.044 mg/mL and (4) propylparaben, 0.053 mg/mL. Buffer: 10 mM phosphate at pH of 6.1 and 40 mM SDS. B: Almay, 32 mg/mL in buffer solution. C: Massengill, diluted 4:10 with buffer solution. An additional 60 percent of the original imidurea component degrades during this heating interval. After 12 hours at 180øC, the corresponding electropherogram (Figure 3C) illustrates distinct peaks at approximately ! 1 and !9 minutes while bands with elution times between six and nine minutes have decreased significantly. Approximately 66 percent of the imidurea component undergoes thermal degradation during the 12- hour heating period. QUANTITATION OF PRESERVATIVES IN COMMERCIAL PRODUCTS Separation of commonly encountered parabens from imidurea was achieved by MEKC

200 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Preservative Concentrations in Commercial Products* Concentration in product** Preservative Product/preservative A B added (mg/mL) Percent recovery Massengill © Imidurea 0.853 0.828 0.0711 98.8 0.1422 100.9 0.2134 101.7 Methylparaben 0.312 0. 320 0.0278 105.9 0.0555 98.6 O.O832 99.O Propylparaben 0.081 0.087 0.0076 100.3 0.0152 99.1 O.O228 98.7 Almay © Imidurea 0. 304 0. 293 Methylparaben 0.201 0.183 Ethylparaben 0. 102 0. 106 0.0115 96.1 0.0229 98.9 0.0343 98.0 0.0112 100.1 0.0224 105.7 0.0336 101.6 0.0222 109.1 0.0444 107.1 O.O666 99.1 * Concentration of preservatives in Massengill and Almay are in units of mg/mL and (w/w)%, respectively. ** A: assay values are the average of duplicate determinations of the sample solutions B: values determined by method of standard additions. with the addition of sodium dodecyl sulfate (SDS) to the previously described buffer (Figure 4A). The products in Figure 4 were diluted with buffer and analyzed without any additional pretreatment. In the case of Massengill, the sample was diluted 4/10 (v/v) with buffer solution, whereas the weighed portion of Almay was dissolved in buffer solution to yield a concentration of 32 mg/mL. Three parabens and imidurea present in several commercial preparations are very well resolved by MEKC, as can be observed in Figures 4B and 4C, where the elution order of the parabens corresponds to the hydrophobic character of the parabens imidurea Table II Limits of Detection of Preservatives Detection limits Component }xg/mL pg Concentration range (}xg/mL) of standard solutions Imidurea 9.9 125 10-400 (r = 0.9996) Methylparaben 1.9 24.6 2.0-40 (r = 0.9998) Ethylparaben 3.4 43.5 3.5-70 (r = 0.9996) Propylparaben 2.5 31.2 2.5-50 (r = 0.9999)