The requirements for validation of the S2 RANGER for process control in pharmaceutical labs are significantly lower.

Determination of Titanium Dioxide and Zinc Oxide
in Sunscreen Products by EDXRF

Introduction

       Ultraviolet radiation from the sun is responsible for increased rates of skin cancer. To prevent sunburn and to reduce the chance of skin cancer, sunscreen products have been developed to reflect or absorb ultraviolet radiation. Metal oxides such as titanium dioxide and zinc oxide are added to sunscreens to reflect ultraviolet radiation. The term Sunblock is often used where titanium dioxide and/or zinc oxide are part of the formulation.

       Traditionally, the analysis of titanium dioxide is very difficult due to the insolubility of titanium dioxide in most solvents. Most analytical techniques involve the hazardous digestion of titanium dioxide in very concentrated acids like sulfuric, nitric or hydrofluoric acids. This preparation is then followed by dilution and then analysis by Inductively Coupled Plasma Optical Emission spectrometry (ICP-OES) or Atomic Absorption Spectrometry (AAS). An alternate option is to further treat the digested solution with hydrogen peroxide to produce a yellow color which is measured at 410 nm by UV visible photo spectrometer. X-ray fluorescence spectrometry has the dual advantage of a simple, non hazardous sample preparation and a short analysis time. Other compounds of interest such as iron oxide can also be determined at the same time.
In this application report the energy dispersive X-ray fluorescence spectrometer (EDXRF) S2 RANGER (see figure 1) has been used to determine the concentration of titanium dioxide and zinc oxide in commercially available sunscreen products.

Instrumentation

       The S2 RANGER is distinguished from conventional EDXRF instruments by its innovative design. With direct sample excitation geometry and a maximum excitation power of 50 W, the S2 RANGER’s beam path results in high detection sensitivity for all elements. The Silicon Drift Detector (SDD) technology of the XFlash® detector offers excellent resolution, even at high input count rates. This combination of direct excitation beam path and high resolution leads to the outstanding analytical performance of the S2 RANGER.

       The easy and intuitive touch screen operation of the S2 RANGER makes the instrument especially useful in pharmaceutical settings. The TouchControl™ interface is easy to learn and failsafe to operate even for new or inexperienced users. After calibration, the external computer can be removed which prevents modification of calibrations and ongoing requirements for validation.

Sample preparation

       Standards and samples were heated to 60 °C for one hour and mixed at 15 minute intervals in order to have a homogenous sample. Ten grams of sample were transferred to a liquid cup with a 3.6 µm Mylar® film.

Results

       Sunscreen products are viscous liquids and the challenge is to get representative samples. To check the repeatability of the sampling and analysis, a tube of sunscreen has been emptied into a beaker and heated in an oven for one hour mixing at 15 minute intervals. Then the same sample has been prepared for 10 times and measured on the instrument. The results are shown in Table 1.

Conclusion

       As can be seen it is possible to analyze sunscreen samples for both TiO2 and ZnO. The sample preparation method is very simple. Analysis in air atmosphere instead of helium is possible and is further reducing the operational costs.

       When used in a pharmaceutical laboratory, the design of the S2 RANGER is such that once the system has been calibrated, the external computer can be removed preventing the modification of calibrations and ongoing requirements for validation. The requirements for validation of the S2 RANGER for process control in pharmaceutical labs are significantly lower.

 Credit : Bruker Co., Ltd.