The ATR-IR technique employed in this study uses the ratio of the peak height of the silicone band near 796.5 cm-1 (tangent baseline), to an area slice of a hair reference band from 940.1 cm-1 to 919.9 cm-1 (tangent baseline) to determine the relative surface silicone level, as shown in Eq. 1.
This method of surface silicone measurement was shown to have a correlation with total extracted silicone levels across a range of 300–4000 ppm. The total silicone deposited on each tress as a function of the conditioning polymer present in the shampoo was measured by extracting the silicone deposit from the tress with solvent and quantifying the total amount of silicone from the infrared spectrum of the dried extract. This method has been validated for 30–5,000 ppm silicone oil levels.