Spherical quartz vessels containing an iodide/iodate chemical actinometer are useful for measuring the fluence of omnidirectional germicidal radiation. It is shown here that such vessels can be used not only for exposure purposes but also for measuring the absorbance of the resulting triiodide endpoint. A hand-held commercially available colorimeter using a 420 nm LED light source was adapted to hold the spheres in the optical light path. The absorbance at 420 nm obeyed Beer’s Law and the dose response showed linear kinetics following irradiation at 254 nm. The determination of the fluence obtained in this manner was consistent with that obtained following transfer of the contents of the spheres to a 1 cm cuvette and measuring the absorbance at 352 nm in a conventional spectrophotometer. Hence, dose response data can be obtained making absorbance measurements on the same sample following sequential or continuous irradiation. Furthermore, because the expression for the fluence is independent of the radius of the sphere, there is no need to measure and keep track of the volume of each sphere, thus simplifying the experimental procedure. Furthermore, the use of an inexpensive colorimeter circumvents the need for a more expensive spectrophotometer and allows measurements to be made in the field.
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