JOURNAL OF COSMETIC SCIENCE 230 Figure 4. Typical chromatograms for standard mix (top), glycerin sample (middle), and glycerin sample spiked at USP limits of 0.10% EG and 0.10% DEG to demonstrate how sample at compliance threshold would appear (bottom). Figure 3. Chromatograms detailing injection of EG-DEG mixed standard (top), reagent blank (middle), and concentrated EG-DEG (bottom) to positively identify EG and DEG peaks. guidelines. For DEG, the %RSD was 0.06 for retention times and 1.09 for peak areas, with a tailing factor of 1.00, also meeting cGMP guidelines. Full cGMP validation of this test procedure was not performed, as any values measured above 0.10% would render the mate- rial out of compliance, and so determining how far a sample might be out of compliance is not the goal of either this test or the USP-NF tests. Figure 8 demonstrates reproducibility. Since sample #39191-2 was assayed at below detection limits for EG and DEG, it was used for spiking/recovery studies (Figure 9). Sample #39191-2 was spiked at two known levels with EG and DEG, then assayed. Recoveries of the sample spiked with 0.0792%

SIMULTANEOUS GC ASSAY OF DEG AND EG 231 Figure 6. Typical chromatograms for standard mix (top), sorbitol solution sample (middle), and sorbitol solution sample spiked at USP limits of 0.10% EG and 0.10% DEG to demonstrate how sample at compli- ance threshold would appear (bottom). Figure 5. Typical chromatograms for standard mix (top), propylene glycol sample (middle), and propylene glycol sample spiked at USP limits of 0.10% EG and 0.10% DEG to demonstrate how sample at compliance threshold would appear (bottom). and 0.1584% EG were 93.8% and 93.2%, respectively. Recoveries of the sample spiked with 0.0831% and 0.1662% DEG were 102.9% and 103.4%, respectively. DISCUSSION This test procedure is offered as a single simplifi ed alternative to six separate DEG and EG test procedures specifi ed in the USP-NF. This test procedure enables a single mixed standard and one set of GC conditions to be used that would replace fi ve separate USP GC