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)

DETERMINATION OF IMIDUREA 201 elutes with the electroosmotic flow (to). Peak identification and peak purity of the parabens were confirmed by examination of PDA spectra. Neither imidurea nor the imidurea-related impurities are affected by the presence of micelles in the mobile phase due to highly hydrophilic character under these electrophoretic conditions. Buffer solutions of both commercial products were spiked at three different concentra- tion levels with the appropriate preservatives, and the percent recovered is shown in Table I along with the amount of preservatives found in each product. All recovery data are from duplicate determinations. The amount of preservative estimated from the spiked sample agrees well with the assay values, which are also reported in Table I. The detection limits appearing in Table II were determined using peak heights at a signal-to-noise ratio of six, with standard solutions encompassing the reported concen- tration ranges. A three-second injection period (5-in Hg) was used, which permitted an injection aliquot of 1.26 nL of sample. CONCLUSION The percent purity of imidurea in the commercial product was calculated to be 96.6%. Total analysis time by CZE was less than fifteen minutes with both minimal sample preparation and sample consumption. A minimum of twenty anionic species in addition to the major neutral component were detected and will be the subject of a CZE-MS investigation in the near future. With the addition of SDS to the electrophoretic buffer, imidurea and the parabens were separated. The determination of preservatives in two commercial products without any extensive sample preparation and method optimiza- tion illustrates the advantage of capillary electrophoresis with detection limits ranging from 25 to 125 picrograms at 190 nm. If an increase in sensitivity is desired, a capillary of wider inner diameter can be used without any significant loss in efficiency, since the current observed is less then 20 IxA. REFERENCES (1) P. A. Berke and W. E. Rosen, Germall, a new family of antimicrobial preservatives for cosmetics. Amer. Perfum. Cosmet., 85, 55-59 (1970). (2) W. E. Rosen and P. A. Berke, Modern concepts of cosmetic preservation, J. Soc. Cosmet. Chem., 24, 663-675 (1973). (3) D. S. Ryder, The thin layer chromatographic detection and determination of an imidazolidinyl antimicrobial preservative, J. Soc, Cosmet. Chem., 25, 535-544 (1974). (4) C. H. Wilson, Identification of preservatives in cosmetic products by thin-layer chromatography, J. Soc. Cosmet. Chem., 26, 75-81 (1975). (5) E. P. Sheppard and C. H. Wilson, Fluorometric determination of formaldehyde-releasing cosmetic preservatives, J. Soc. Cosmet. Chem., 25, 655-666 (1974). (6) F. E. P. Mikkers, F. M. Everaerts, and T. P. E. M. Verheggen, High-performance zone electropho- resis,.]. Chromatogr., 169, 1-10 (1979). (7) F. E. P. Mikkers, F. M. Everaerts, and T. P. E. M. Verheggen, Concentration distribution in free zone electrophoresis, J. Chromatogr., 169, 11-20 (1979). (8) J. W. Jorgenson and K. D. Lukacs, Zone electrophoresis in open-tubular glass capillaries, Anal. Chem., 53, 1298-1302 (1981).