Iodouracil as a personal dosimeter for solar UVB.

A solution of iodouracil (0.2 mg/mL) and KI (0.1 M) in 0.23 M borate buffer (pH 7) forms triiodide upon exposure to UVB. In the presence of thyodene, the blue starch-iodine complex is formed, the intensity of which is proportional to the amount of UVB exposure. Studies were conducted using either a sunlamp or solar irradiation to generate the triiodide endpoint. Samples (1 mL each) were placed in a plastic 24 well sample holder for exposure, and the intensity of the light at each well was controlled by placing a template over the holder with apertures of various sizes (0.4-1.5 cm) to vary the amount of light incident on each sample. The endpoint was measured using a spectrometer to monitor the absorbance increase at 400 nm of each sample or a densitometer to monitor the optical density of a photograph of the resulting solutions. The selectivity for UVB was demonstrated by irradiating through a UVB cutoff filter that reduced the sunlamp yield by 98.5% and the solar radiation yield by 94%. The correlation between the observed absorbance changes at 400 nm and the amount of absorbed energy was shown to be approximately the same for both types of radiation and the resulting quantum yield calculated to be approximately 1%, consistent with the value obtained previously for 5-iododeoxyuridine using monochromatic radiation. It is proposed that this system be incorporated into a personal dosimeter for monitoring solar UVB exposures, where the degree of exposure can be estimated either by visual inspection or, for more quantitative analysis, by UV spectroscopy.