TiO₂ and ZnO in Lotions

Scope

The measurement of titanium dioxide (TiO₂) and zinc oxide (ZnO) in lotions is demonstrated.

Background

TiO₂ is added to lotions, creams, and various cosmetics as a whitening agent and acts as a sunscreen. ZnO is added as a sunscreen and is very effective at blocking UV light. Its concentration is a factor in determining the SPF (sun protection factor) of lotions and creams. ZnO is also a mild astringent with mild antiseptic properties used in lotions and creams to help retain moisture, provide a protective layer to the skin, and prevent diaper rash in baby products. When iron oxide (Fe₂O₃) is also added the TiO₂ (white) and Fe₂O₃ (red) are blended in various proportions to create the many shades of reds and browns in cosmetics, make-up, rouge, and lipsticks.

Model: NEX QC+

Calibration

Calibration is a one-time procedure using standard empirical regression. In this demonstration, eight calibration standards with independently varying levels of TiO₂ and ZnO were used. Automatic correction factors are calculated by the calibration to compensate for X-ray absorption/enhancement effects between Ti and Zn.

TiO₂

Correlation plot TiO₂ in lotion

ZnO

Correlation plot ZnO in lotion

Recovery and repeatability

Repeatability (precision) is measured using 10 or more repeat measurements. Low and high calibration standards were analyzed with 10X repeats to demonstrate effective recovery and analytical precision.

Conclusion

The Rigaku NEX QC+ is a compact, simple to operate tool, ideal for at-line quality checks during production as well as in the QC lab. Similar results can also be obtained on NEX QC using slightly longer measurement time. For cosmetics that include Fe₂O₃, simply create standards containing the TiO₂, ZnO and Fe₂O₃, the Fe₂O₃ performance is comparable to the ZnO data shown here.