DETERMINATION OF 1,4-DIOXANE 331 Table I Calibration data: Direct injection method ppm Counts RSD (_+) 1 1.43 x 105 6% 2 2.28 X 105 1 10 12.4 X 105 2 100 123.5 X 105 2 1000 1213.0 X 105 1 REAGENTS (a) 1,4-Dioxane--Fisher certified reagent grade. Stock solution (1000 ppm) prepared by pipetting 0.97 ml (1.000 gm) of dioxane into a l-liter volumetric flask, diluting to volume with HPLC grade water and mixing. Calibrating solutions were prepared by appropriate serial dilution of stock solution with HPLC grade water. (b) IVater--Baker HPLC grade water. (c) Methanol--Fisher ACS certified reagent grade. PROCEDURES SAMPLE PREPARATION Most low viscosity samples were injected as supplied. High viscosity samples were diluted 1:1 with either water or methanol prior to injection. PEG was dissolved in 2.0• o - 1.5- x I:L - • - Z _ O i I I0 I00 PPM DIOXANF' Figure 2. Calibration curve. i I000

332 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS methanol (50% w/v). Samples analyzed by the standard additions method were diluted 1:1 with an appropriate concentration of 1,4-D solution, mixed, and injected. 0.1% of 1N KOH was added to all samples to prevent dioxane formation in the injection port. CHROMATOGRAPHY Generally 10 •1 of neat sample or 20 •1 of 1:1 diluted sample was injected onto the precolumn, and the program timer started. Concentration of 1,4-D in the samples was determined by interpolation on a standard curve constructed by injection of 10/xl samples of the appropriate 1,4-D calibration standards. RESULTS AND DISCUSSION Preliminary experiments to determine the range and linearity of the method produced the results tabulated in Table I. Mean counts and RSD (Relative Standard Deviation) are based on the digital integral of the dioxane peak from five replicate injections of each aqueous standard. The precision at the 1 ppm level is limited by the precision of TIME ,MIN. TEMP ,øc IO 20 I Figure 3. Typical chromatogram of a 1 ppm Standard (10 gtl direct injection injection temperature--60ø program 10 min at 80 ø, 20ø/min to 170 ø, hold 10 min).