METHOD FOR SILICONES ON HAIR 385 INSTRUMENTATION The atomic absorption assay was performed on a Perkin Elmer Model 380 spectrometer with a silicon hollow cathode lamp and a 5-cm slot nitrous oxide-acetylene burner. Samples were prepared with the aid of a Burrell wrist-action shaker and an IEC Clin- ical © model 428 centrifuge, equipped with a 6 X 52-ml angle rotor and 50-ml shields. Photos were taken on Polaroid Polapan Type-52 film, through the objective of a JEOL T300 scanning electron microscope. Hair samples were mounted on an aluminum tab with double-sided tape and then gold-sputtered for 50 seconds. The tab was then mounted in the microscope and the samples viewed without tilting the stage. No dif- ference in image resolution was detectable by rotating the angle of the stage. The photos were taken at a magnification of 2000 x. SPECIFIC SILICON ASSAY TEST PROCEDURE [Special note: As this is a trace elemental analysis technique, care must be taken during sample preparation to avoid inadvertent contamination of the samples and reagents. Latex gloves should be worn if the analyst has used silicone-containing cosmetics, to avoid sample contamination.] Sample preparation procedure. Using solvent-cleaned scissors, about 50-75 hair fibers were cut from each previously treated, dried hair tress to be evaluated. The fibers from the tress were cut just below the (carnauba-waxed) bound end of the tress, clipping off and discarding the upper 2.5 cm of these hairs (root end). The remaining fibers were cut into approximately 0.3-cm length clippings with the clean scissors. Individual samples were prepared by weighing 0.10 _+ 0.02 g of the clipped hair into a tared vial, using solvent-cleaned tweezers. The hair sample weight was recorded to use for calculating mg/kg Si from the reported AAS results. Samples were then diluted with 10.0 _+ 0.10 g of enzyme solution, as prepared in the formula below: Papain enzyme 0.13 -+ 0.02 g Sodium sulfite 2.00 _+ 0.10 g Distilled water 100.00 _+ 0.10 g [Shaken until dissolved, then adjusted to pH 6.8 with HC1 (conc.). This recipe is enough for nine samples and a blank. Fresh enzyme solutions should be prepared for each day's testing.] Each vial was then capped and shaken lightly to wet the hair clippings. A blank sample, of just 10.0 g of enzyme solution, was also prepared. All of the samples were then placed in a block heater or in an oven set at 63øC _+ 3 ø for three days, swirling each sample at least once during the heating cycle to make sure that all of the hair sample is in the solution and not adhering to the sides of the vial. To each sample, seven milliliters of methyl isobutylketone (MIBK) and five hundred microliters (0.5 ml) of concentrated reagent hydrochloric acid were added. The samples were then placed in a Burrell mechanical shaker and agitated for 30 minutes. The extraction vials were then spun in an IEC Clinical © centrifuge at moderate speed for 20-30 minutes to permit phase separation. The 4.0-dram vials will fit into 50-ml centrifuge shields. Following separation, the top (solvent) layer of each sample is drawn off with a transfer pipet and reserved in a new vial for AAS analysis.

386 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Instrument calibration and sample analysis. Silicon was determined in the extracts by AAS, using a nitrous oxide-acetylene flame. The atomic absorption spectrometer initialization procedure followed the manufacturer's recommended values (i.e., for gas flows and lamp current). The 251.6-nm silicon wavelength was used. After the instrument warm-up period, the gas flow, nebulizer uptake, and burner head alignment adjust- ments were made while aspirating a Dow Corning © 200 fluid-MIBK solution con- taining 60 to 70 •xg Si/ml. The final optimization adjustments for best sensitivity and signal-to-noise ratio were made while aspirating the water-saturated blank solvent and calibrating solutions. Calibration in both wet and dry solvent solutions was necessary because silicon is very sensitive to small changes in flame temperature. The water which saturates the MIBK during the solvent extraction step alters the temperature and fuel-oxidant stoichiometry of the N20-C2H2 flame. The atomic absorption response for silicon in wet MIBK is perhaps reduced to 70% as compared to the same quantity of silicon in dry MIBK. Dry MIBK silicon calibration solutions were prepared from Dow Corning © 200 fluid, which has a polymer repeating unit molecular weight of 74. ! g/unit of Me2SiO. It contains 37.9 percent silicon. Viscosity grades between 100 centistokes and 1000 cen- tistokes are permissible for use as standards. For a typical standard, 50 mg of DC 200 fluid was weighed into a 250-ml flask partially filled with MIBK. DC 200 fluid tends to adhere to dry glass surfaces and may require a long contact time with the solvent to ensure complete solubility of the entire sample. An exact weight of 50 mg is not essential, but that weight in 250 ml will result in a silicon concentration of 75 }zg of silicon per milliliter of solvent, or 75 mg/kg Si on a wt/volume basis. The calibration plot of Si concentration vs. absorbance was linear from the zero inter- cept through a silicon concentration of 75 mg/kg provided that the atomic absorption spectrometer was set up under optimum conditions. The exact silicon concentration was calculated using the following equation: Sample weight (milligrams + 0.1 mg) x 28.1 x 1000 74.1 x 250ml = micrograms of Si per ml This weight/volume silicon standard may be serially diluted with MIBK to produce calibrating solutions lower in silicon content as required. To make the wet solvent standard calibration solutions, an aliquot of the standard was shaken with an excess of water, which was centrifuged out, prior to use. For example, to a 25-ml aliquot of calibrating solution, five ml of water and 0.25 ml of concentrated HCI reagent were added. Dry standards can be stored and will remain constant, but wet standards deteriorate on standing and so were made anew for each day's testing. In addition to the standards, the background solvent which is aspirated into the instru- ment between samples must also be water-saturated. A supply of MIBK stored over water was maintained to use for background solvent. Samples were aspirated into the AA spectrometer, and the absorbance values at 251.6 nm were recorded along with the absorbance values for the wet calibrating solutions. A calibration plot of absorbance vs. silicon concentration was constructed. The concentra- tion of silicon in the sample extracts was recorded from the calibration plot, and then multiplied by the extract solvent volume of 7 ml to obtain the total weight of silicon