Monte Carlo modelling of a new sample-holder design for UV–Vis spectroscopy

Introduction: Spectrophotometry is a well-established technique widely employed in chemistry, biology, medicine research, and industrial applications. It plays a crucial role in environmental testing, detecting pollutants in water and air. Many spectrometer models adopt a quartz cuvette. We investigated the replacement of the cuvette with a new sample holder coupled with SiliconPhotoMultiplier. Methods: This new holder, with the shape of an integrating sphere, offers several advantages since it is much less affected by sample stratification and turbidity. Furthermore, the high reflectivity of the cavity walls lets the light cross the sample many times, enhancing the sensitivity. We implemented a detailed Geant4 simulation to optimize this new sample holder and to provide its first characterization. A double-line spectrophotometer was assembled with two newly designed holders. The system foresees a pulsed light source. If the source emits a continuum spectrum, as in the case of pulsed Xenon lamps, a monochromator is mandatory for wavelength selection. The light is transmitted using solarized optical fibres and is split in half to feed the two identical sample holders. The emerging light is conveyed to the Silicon Photomultipliers. One holder is filled with ultrapure water, as a reference, while the other contains a solution of ultrapure water and a contaminant. Results: We inferred the inner walls’ reflectivity by measuring the stretching of a narrow light pulse. A preliminary measurement with an aqueous solution of NaNO3 provides a detection limit of 40 mg/L. Conclusions: We propose a new sample-holder design to improve the sensitivity of spectroscopy.