JOURNAL OF COSMETIC SCIENCE 214 RESULTS Calibration of FTIR-ATR for aqueous emulsifi cations of dimethicone yielded outstand- ing linearity for a 12-level series of standards up to 35% (r2 = 0.9997) as shown in Figure 2. The excellent precision of the FTIR-ATR method was demonstrated by repeated anal- ysis of selected calibration standards, yielding relative standard deviations of less than 0.3% (Table II). Five different retail O TC wipe products with label claims in the range of 3–5% emulsi- fi ed dimethicone were analyzed. Analytical results from all three methods (Table III) compared favorably with label claims and with each other. The agreement between stan- dard addition and external calibration (Methods 2 and 3) for fi ve different wipe products is a strong indication that there is no matrix interference with this method. This was further verifi ed by the dimethicone test results in the presence of various surfactants and preservatives shown in Table IV. No statistically signifi cant interference was observed for any of the ingredients tested. CONCLUSIONS Direct test ing of dimet hicone in aqueous emulsions by FTIR-ATR is a viable method that has been ignored in the past. Dimethicone is a rare analyte that may be analyzed by FTIR-ATR in the presence of large quantities of water because of its unique absorption frequency at 1,260 cm-1. It may, in fact, be accurately measured across a wide range of Table II Replicate FTIR-ATR Assays of Standards Dimethicone conc. (%) Average (n = 6) RSD (%) 3.00 3.01% 0.27 12.00 12.00% 0.15 21.00 21.00% 0.18 30.00 30.03% 0.26 Table III Results of Three Analytical Methods—% Dimethicone (g/100 g) Wipe samples Method 1 (n = 6) Method 2 (n = 6) Method 3 (n = 6) Product Claim (%) Average (%) RSD (%) Average (%) RSD (%) Average (%) RSD (%) A 3.2 3.31 3.29 3.26 0.30 3.12 11.7 B 3.6 3.65 4.71 3.70 0.37 3.74 9.26 C 3.0 3.19 5.85 3.05 0.27 3.09 15.7 D 3.0 3.25 5.17 3.14 0.24 3.30 13.1 E 5.0 5.20 3.71 5.23 0.23 5.50 7.08 Six separate replicates of each product were tested by the three methods: Method 1: Extraction in hexane FTIR transmission . Method 2: Emulsion (no extraction), FTIR-ATR, external calibration . Method 3: Emulsion (no extraction), FTIR-ATR, standard addition .

DIRECT ANALYSIS OF DIMETHICONE IN AQUEOUS EMULSIONS 215 concentrations while still in aqueous emulsions. This rapid method of analysis will be helpful in quality testing to support manufacturing and stability testing of products that contain dimethicone emulsions. Direct analysis of samples without sample preparation is appealing compared with more lengthy, complex methods. Of course, as with all new analytical procedures, this method should be validated on a product-by-product basis because other ingredients and excipients could potentially interfere with this procedure. ACKNOWLEDGMENT This work was supported b y the Center for Chemical Technology at Weber State University. REFERENCES (1) “Dimethic one,” Toxic o logy Data Network, U.S. National Library of Medicine, accessed April 8, 2019, https://toxnet.nlm.nih.gov /cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+1808. (2) P. K. Farris, “Topica l Skin Care and the Cosmetic Patient,” in Master Techniques in Facial Rejuvenation, (Elsevier Health Sciences, Atlanta, GA, 2018), pp. 68–72. (3) E. S. Ihde, J. R. B os camp, J. M. Loh, and L. Rosen, Safety and effi cacy of a 100% dimethicone pedicu- locide in school-age children, BMC Pediatr., 15, 70–76 (2015). (4) J. Heukelbach, D. P il ger, F. A. Oliveira, A. Khakban, L. Ariza, and H. Feldmeier, A highly effi cacious pediculicide based on dimethicone: randomized observer blinded comparative trial, BMC Infect Dis., 8, 115–124 (2008). Table IV Effect of Various Excipients on Method 2 Assay Results Excipient added Excipient conc. (%) Dimethicone % averagea (n = 3) RSD (%) Control 0.00 3.01 0.51 Laureth-4 0.30 2.96 1.60 0.60 3.02 2.32 Laureth-23 0.30 3.05 1.68 0.60 3.06 1.68 Triton X-100 0.30 2.95 1.55 0.60 3.03 2.70 PPG-15 stearyl ether 0.30 3.00 2.03 0.60 3.01 2.03 PEG-100 stearate 0.30 3.01 2.82 0.60 2.95 1.74 Sorbitan laurate 0.30 3.02 2.82 0.60 2.95 1.60 Methylparaben 0.05 2.99 1.65 0.10 2.99 0.84 Propylparaben 0.05 3.01 0.96 0.10 3.00 1.17 Phenoxyethanol 0.05 2.99 0.67 0.10 3.00 1.07 DMDM hydantoin 0.01 3.00 1.68 0.02 3.02 1.15 Kathon 0.0050 2.97 0.19 0.0100 3.00 1.39 Sodium benzoate 0.05 3.01 1.45 0.10 3.00 1.15 a Actual dimethicone concentration in all samples = 3.00% (g/100 g) .