DETERMINATION OF 1,4-DIOXANE 99 Table I Reproducibility of Response Ratio Area isobutanol Area 1,4-dioxane Response ratio 147436 56600 2.60 148348 59739 2.48 156260 60161 2.60 159059 60291 2.64 164563 65101 2.53 163548 63199 2.59 159638 63356 2.52 154759 62834 2.46 Average response ratio = 2.55. Standard deviation = 0.06. Relative standard deviation = 2.5%. sample was allowed to sit until it dissipated (approximately 15 minutes). This sample solution was analyzed directly using the gas chromatographic program described below. GAS CHROMATOGRAPHIC CONDITIONS The gas chromatographic system was a Hewlett Packard 5890A equipped with a flame 1.50e+6 - 5.00e.• 0.00©+0 y = - 1.B7e+4 + 5046.gx R^2 = o.ggg8 i 50 100 150 200 250 PPM DIOXANE Figure 1. Linearity of 1,4-dioxane standards from 1 ppm to 250 ppm.

100 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ionization detector. The output signal was sent to a Nelson Analytical data system. The column used was a 12-foot x Vs-in stainless steel packed column of 15% OV-1 on 100/120 Chromasorb WHP (Supelco, Inc., Bellefonte, PA). The injector temperature was 185øC and the detector temperature was 325øC. The column temperature program was: 85øC for 2 minutes, followed by a linear temperature increase of 5øC/min to 95øC, with a hold of 1 minute. This was followed by a cleanup step involving a temperature increase of 25øC/min to a temperature of 300øC, where it was held for 5 minutes. The helium carrier flow was 40 ml/min, and a 1-•1 direct injection was made into a quartz injection port liner loosely packed with silanized glass wool. RESULTS AND DISCUSSION It was necessary to determine if a sample prepared by this method would be homoge- neous and if it could be reproducibly analyzed. To confirm this, a sample of Shampoo B was prepared in the prescribed manner and analyzed nine times to determine the reproducibility of the response ratio. The resulting response ratios were determined as the area of isobutanol compared to the area of 1,4-dioxane, and are tabulated in Table I. The response ratio for this test mixture was determined to be 2.55 - 0.06 with a relative standard deviation of 2.5%. This confirms that the sample preparation results in a homogeneous mixture. -20 - 1 0 y= 13.8+ 0.9x R^2 =0.9996 ß I ' I ' I ' I 0 10 20 30 40 PPM DIOXANE SPIKED Figure 2. Standard addition of 1,4-dioxane into Shampoo B.