Analysis of Dimethicone (Dimethylpolysiloxane) in Hair Care Products

Dimethicone (dimethylpolysiloxane) is a type of silicone oil widely used as an emollient in hair care products, such as conditioners and shampoos, due to its water repellent properties.

Fig. 1 shows the structure of dimethicone, which is a strongly hydrophobic compound in which the dimethylsiloxane group is polymerized. Its application varies according to the degree of polymerization. As dimethicone exhibits virtually no UV absorbance, an evaporative light scattering detector provides an effective means to detect it.
Presented here is an analysis of dimethicone in hair care products using the ELSD-LD II evaporative light scattering detector.

The Presto FF-C18 silica-based nonporous ODS column (Imtakt USA) was used for analysis. Fig. 2 shows the chromatogram obtained from analysis of a dimethicone (1000 cSt) standard solution (THF solution) using the analytical conditions shown in Table 1.

The Presto FF-C18 silica-based nonporous ODS column (Imtakt USA) was used for analysis. Fig. 2 shows the chromatogram obtained from analysis of a dimethicone (1000 cSt) standard solution (THF solution) using the analytical conditions shown in Table 1.

Table 1 Analytical Conditions

Fig. 2 Chromatogram of Standard Solution
(500 mg/L, 2 μL injection volume)

Fig. 3 shows the chromatogram of a commercially-available hair conditioner containing dimethicone. 5 mL tetrahydrofuran was added to 450 mg hair conditioner. Analysis was performed after agitation, ultrasonic extraction, and filtering of the supernatant through a 0.22 μm membrane filter. Fig. 3 shows the resulting chromatogram.

This indicates that the combination of ELSD-LT II and gradient elution permits the efficient detection of substances that are difficult to detect with a UV detector.

Fig. 3 Chromatogram of Hair Conditioner
(2 μL injection volume)