SIMULTANEOUS GC ASSAY OF DEG AND EG 229 and chromatography by reacting with active hydrogens of the hydroxyl groups even though an active hydrogen is replaced by a heavier trimethylsilyl group, the resulting derivative is usually more volatile and delivers sharper peaks due to the polarity of the molecule being decreased. For example, for glycerin (Figure 2), the following technique was employed. This technique was published by this author in 1987 for quantitation of glycerin in consumer products at both use levels and trace levels (8) and was considered for application to the issue of EG and DEG quantitation at low levels. Standards were prepared by dissolving DEG and EG in N,N-dimethylformamide solvent (DMF) and mixing with BSTFA reagent in autosampler vials samples were prepared similarly, as was a reagent blank. Since DMF and BSTFA reagent are not much more volatile than derivatized EG, the GC oven program was initiated at 90°C, held there for 4.0 minutes, and then programmed to remove the derivatized polyol components off the GC column prior to the next injection. Either the DMF-BSTFA reagent blank or a concentrated standard EG-DEG-BSTFA mix could be used to positively identify which peaks were EG and DEG. Routine external standard quantitation was used the assay was straightforward. RESULTS A sample of real-world USP grade glycerin, a sample of propylene glycol, a sample of USP 70% sorbitol, two suppliers’ samples of PEG-8, two suppliers’ samples of PEG-12, and three suppliers’ samples of PEG-6 methyl ether were assayed (Figs 3–7). All the samples assayed above would meet current USP-NF DEG and EG level requirements. The glycerin, propylene glycol, and sorbitol solution were below detection level (BDL). The results are detailed in Table I. Small artifact peaks in reagent blanks (and in standards and samples) when using BSTFA trimethylsilyl derivatization have been well-documented in the literature (13,14) but do not elute near the retention times of DEG or EG, and so these do not interfere with the assay one such artifact typically found is C5H7N2OF3. ACCURACY AND PRECISION System suitability calculations for the above had %RSDs of 0.10 and 1.24 for the EG retention times and peak areas, respectively, and a tailing factor of 0.99, all within cGMP Figure 2.

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%