208 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (10) yet the lack of specificity of the flame ionization detector (FID) used and the fact that application of the method is restricted to shampoo products are disadvantages. In a previous paper (9), we described the first reversed-phase high-performance liquid chromatographic (RP-HPLC) method with UV spectrophotometry for the rapid assay of 1,4-dioxane in different cosmetic preparations. However, the selection of short UV wavelengths (9) for the detection of this compound lacking a strong chromophore generally results in low selectivity, due to increased interference from matrix constitu- ents. Routine analyses of 1,4-dioxane in cosmetics necessitated a simple method possessing a high degree of specificity and the required sensitivity. This study describes a procedure for the assay of 1,4-dioxane in cosmetic products by GC-mass spectrometry (GC-MS) using selected-ion monitoring (SIM). Prior to GC-MS analysis, rapid and efficient purification of the complex cosmetic matrices is achieved with combined silica- and octadecylsilica-disposable cartridges. The application of the method to the determina- tion of 1,4-dioxane in a wide range of commercial cosmetics is also reported. EXPERIMENTAL MATERIALS HPLC-grade 1,4-dioxane, hexane, dichloromethane, toluene, and acetonitrile were sup- plied by J. T. Baker (Phillipsburg, NJ). Bakerbond C•8 (BB-C•8), Bakerbond CN (BB-CN), and Bakerbond silica (BB-SiOH) cartridges were obtained from J. T. Baker. Commercial cosmetics containing ethoxylated surfactants were from retail stores or from manufacturers or importers of these products. GAS CHROMATOGRAPHY-MASS SPECTROMETRY GC-MS analyses were performed with an HP 5890 gas chromatograph (Hewlett Pack- ard, Palo Alto, CA) equipped with an HP 5970 mass-selective detector (Hewlett Packard) with transfer line held at 280øC. Samples (1 }xl) were introduced using on- column injection. A deactivated fused-silica pre-column (5 m x 0.32 mm i.d.) and a Poraplot Q analytical column (25 m x 0.32 mm i.d. Chrompack Italia, Milan, Italy) were used. The operating conditions were: initial temperature, 40øC ramp 40-220øC, rate 40øC/min carrier gas, helium inlet pressure, 100 kPa. The MS, connected directly to the capillary column outlet, was operated in the selected-ion monitoring mode scanning m/z 31, 58, and 88 for 1,4-dioxane and m/z 91 and 92 for toluene (internal standard) with dwell times of 350 ms. The GC-MS system was controlled by an HP 5970 MS Chemstation Rev. 3.2 data station. Quantification was on the basis of peak area for the ratio 1,4-dioxane/toluene. STANDARD SOLUTIONS A 1,4-dioxane stock solution was prepared at a level of 20 mg/ml in acetonitrile, and an aliquot of it was diluted to make standard solutions in the concentration range 0.3-20 }xg/ml. An internal standard solution (5.9 }xg/ml) was prepared by quantitative

1,4-DIOXANE ASSAY 209 dilution of toluene with acetonitrile based upon the expected values of 1,4-dioxane in the cosmetics. The calibration standards were prepared by mixing 2 ml of each 1,4-dioxane standard with 2 ml of the internal standard solution, corresponding to levels of 1,4-dioxane in the cosmetic (0.2 g) in the range 3-200 mg/kg. These solutions were analyzed by GC-MS as reported above, and the response factor relative to the internal standard was deter- mined. SAMPLE PREPARATION Cosmetics were processed by a modification of the method described in an earlier study (9). In brief, the cosmetic product (0.18-0.22 g) was accurately weighed into a 10-ml glass centrifuge tube 4 ml of 20% v/v dichloromethane in hexane were added and the sample was mixed on a vortex mixer and centrifuged at 4500 rpm for 2 min. The extraction was repeated with 1.5 ml of 20% dichloromethane in hexane, and the combined supernatants were applied to a pre-conditioned (2 ml of acetonitrile and then 3 ml of 20% dichloromethane in hexane) BB-SiOH cartridge (sorbent weight, 500 mg) at a flow rate of ca. 1.5 ml/min. The extraction column was then washed with 1 ml of dichloromethane, aspirated to dryness by centrifugation at 3000 rpm for 1 min, and eluted with two 0.8-ml aliquots of acetonitrile. The acetonitrile fraction was passed directly through a BB-C•8 cartridge (sorbent weight, 200 mg), which had previously been primed with 2 ml of acetonitrile. The eluate from the BB-C18 cartridge was made up to volume (2 ml), diluted with the internal standard solution (2 ml), and assayed by GC-MS. RECOVERY AND REPRODUCIBILITY The test samples were prepared by adding 20-•1 aliquots of 1,4-dioxane spiking solu- tions in acetonitrile, corresponding to 40 mg/kg, to the cosmetic products (0.2 g) and mixing them thoroughly. The percentage recovery was determined by comparing the amounts of 1,4-dioxane extracted from samples with those obtained by direct injections of standard solutions. The intra-assay reproducibility was tested by analyzing, on ten different days, 1 •1 of the same stock sample solution from a baby lotion. The inter-assay variability was evaluated by repeated (n = 10) extractions on Bakerbond cartridges and GC-MS anal- yses of the same baby lotion product. RESULTS AND DISCUSSION In a previous investigation (9), solid-phase extraction columns pre-packed with cyano- propylsilica were used for sample preparation prior to assay of 1,4-dioxane in cosmetics by RP-HPLC. Disposable silica cartridges were selected in this study for sample clean- up before GC-MS analysis, since they achieve effective purification of the cosmetic matrices while affording more reproducible recoveries than the cyano-packing. The eluant from the BB-SiOH cartridge was passed directly through a BB-C18 column (see Experimental) to obtain a clear solution suitable for GC injection.