210 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The cool on-column injection technique was chosen because it provides highest GC sensitivity, as 1-•xl volumes of liquid samples were injected directly onto the capillary column through an inlet maintained at a temperature below the boiling point of the solvent (17). The MS of 1,4-dioxane recorded over the mass range of 30-90 daltons has four major fragments, of which m/z 31, 58, and 88 (molecular ion) were selected for SIM recording. Operation of a computer-controlled GC-MS system in the SIM mode provides both specificity and sensitivity (18). By combining the abundance of a number of character- istic ions, the MS functions as a selective detector, eliminating the interfering peaks encountered in GC-FID analysis (6,10) and the need for additional confirmatory meth- ods (9). Moreover, the MS, when adjusted to selected masses for a defined period of time, provides detection limits that are several orders of magnitude lower than are possible in the full-scan mode. Commercial cosmetic products, containing no detectable 1,4-dioxane, were spiked at levels corresponding to 40 mg/kg. The average recoveries (n = 6) and relative standard deviations (RSD) for a day cream, a moisturizing lotion, and a shampoo were 93.2% (RSD, 4.3%), 91.1% (RSD, 3.9%), and 92.4% (RSD, 4.7%), respectively. In con- trast, a previous investigation carried out by GC-FID (6) produced poor recoveries (mean value, 63%) accompanied by a high degree of variability (RSD, 19.9%). Improved recoveries have been obtained by the GC procedures of Rastogi (8) and Italia and Nunes (10), but the lengthy sample preparation (ca. 16 hours) of the former and the limited applicability to shampoos of the latter are disadvantages. The working range of the present method was found to be linear over the concentration interval, 3-200 mg/kg (r 2 = 0.998). Representative GC-MS profiles (SIM mode) of a dioxane-free day cream formulation and of a liquid soap containing 4.6 mg/kg of 1,4-dioxane are shown in Figures ! and 2, respectively. Applying the foregoing GC-MS procedure to a baby lotion, 1,4-dioxane (10.9 mg/kg) was determined with an RSD of 3. !% (n = !0) for the intra-assay reproducibility and of 4.3% (n = !0) for the inter-assay reproducibility. 2000' 1OOO' 17.0 18.0 19.O 20.0 21 .•) 22.0 23.E) 24.0 T•me (m•n.) 25.8 26.0 Figure 1. GC-SIM-MS chromatogram of a day cream preparation. Solvent delay, 16 min. Other operating conditions as described under Experimental I.S. = internal standard (toluene).

1,4-DIOXANE ASSAY 211 1 18.• 19.• 2•.• 21 .•) 22.•) 23.•) 24.0 25.•) 2•.•) 7 lrne (m•n.) Figure 2. GC-SIM-MS trace of a liquid soap product. Conditions and peak identification as in Figure 1 1 = 1,4-dioxane. A variety of commercially available cosmetics were analyzed for 1,4-dioxane according to the method described here. The products (n = 25) included shampoos, liquid soaps, sun creams, bath foams, moisturizing lotions, cleansing milks, after-shave balms, baby lotions, day creams, and hair lotions. Of the total products investigated, 56% contained 1,4-dioxane with levels ranging from 3.4 to 108.4 mg/kg (Table I). The concentrations of 1,4-dioxane in six different cosmetic preparations determined by the present GC-SIM-MS method and by the previously reported HPLC-UV procedure (9) are listed in Table II. The two methods produced consistent results, confirming the validity of the procedure developed in this study. The higher values obtained by GC-MS were traced to improved recovery during sample extraction. The MS is a more sensitive detector than the UV (9) consequently a lower amount of the cosmetic product (0.2 g) is required for the GC-MS assay, which results in a more efficient extraction into the dichloromethane-hexane (20:80) solvent. The results presented in Table I indicate that the control of 1,4-dioxane contaminations in marketed cosmetics should be considered by national and international authorities, particularly to verify the conformance of the commercial products to the existing leg- islation (16). The presence of 1,4-dioxane in a baby lotion preparation (see Table II) Table I 1,4-Dioxane Levels in Cosmetic Products Determined by GC-SIM-MS 1,4-Dioxane (mg/kg) Percentage of total products examined (n -- 25) n.d. 44 3.4-10 16 10-50 28 50-108.4 12 n.d., not detected.