GAS CHROMATOGRAPHY OF METHYLENE CHLORIDE 119 The three sections were connected to the flash vaporizer insert in the order given above with the unions between the sections filled with Porapak Q. The column was conditioned overnight at 200øC with 30 cc/min helium flow. A 1.85 m X 3.2 mm (6 ft X 1/s in.) Porapak Q, 80-100 mesh column was connected to the reference side of the detector. Temperature pro- gramming was used as follows: 160øC for 2 min program to 180øC at 6øC/min and hold for 2 min. The instrument was set up to return the columns to the initial temperature at the end of the program. A commercially available hair spray of known composition, con- taining 50% concentrate and 50% propellant of the composition: 45% Propellant 12, 45% Propellant 11, and 10% isobutane, was used as standard for this work. Two samples of different hair sprays containing methylene chloride were purchased for subsequent analysis. The aerosol can was sampled using a stoppered 10-ml serum bottle and the transfer assembly shown in Fig. 1. Vacuum was drawn on the bottle by inserting the transfer button into a hose connected to a vacuum pump and pushing the needle through the stopper into the bottle. After 2 min the needle was withdrawn from the stopper and the bottle wa• carefully weighed. After removing the button from the aerosol can to be sampled, the transfer assembly was fitted to the valve stem, either with or without the insert, depending on the size of the stem, without actuating it. The bottle was brought down over the needle so it pierced the stopper (Fig. 2). The button was then depressed, allowing the liquid sample to enter the bottle. When the pressure had equilibrated, a tissue was wrapped around the rubber stopper and the bottle, and, with the needle and button held firmly in position with one hand, the bottle was quickly withdrawn from the needle with the other. Some practice was necessary to develop a technique so none of the sample inside the bottle was lost, nor was any of the hair spray contained in the needle permitted to coat the sample bottle giving erroneous sample weights. The bottle was re- weighed to determine the sample weight. Methylene chloride and n-propanol, the internal standard, were added to the sample using a 1-ml hypodermic syringe equipped with a 1-in. X 22-gauge needle. A known volume of the solvent was drawn into the syringe, all air was expelled, and it was injected through the stopper into the bottle. If a constant pressure is maintained on the plunger, the solvent in the needle will form a very effective seal to prevent escape of

120 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 2. Detail of sampling procedure showing (top to bottom) sampling bottle, transfer needle assembly, and aerosol can the sample in the bottle. For the standards used in this work, 10.12 and 10.32%, respectively, of methylene chloride were added. About 0.1-ml of n-propanol, the internal standard, was added per gram of sample taken. Sampling of the bottle also requires some practice to accomplish with reproducibility. A 2-•1 Precision Pressure-Flo high-pressure liquid syringe consists of a needle which can be retracted into a Teflon©* seal with the sample contained inside at pressures up to at least 500 psig. It can then be pressed tightly against agc septurn, the needle inserted, and the sample ejected. The same technique, in reverse, was used to sample the hair spray. The needle was inserted into the inverted sample bottle until the hole could be seen in the liquid. The plunger was worked in and out several times to draw sample into it. The needle was then drawn back very carefully, but not out of the rubber stopper, until the stopper was flush against the blunt end of the sealing tube. The bottle was pressed down so a seal was formed between the rubber and the seal- ing tube. While holding the bottle tightly this way the needle was drawn out of the bottle into the sealing tube. A Vidar-Autolabs 6221* digital integrator was used to determine peak areas. * E. I. du Pont de Nemours & Co., Inc., Wilmington, Del. t Vidar Autolab, 77 Ortega Ave., Mountain View, Calif. 94040.