Photobleaching of Methylene Blue in continuous wave thermal lens spectrometry

In this study continuous wave thermal lens spectrometric measurements are made using solutions of Methylene Blue in short pathlength sample cells (0.1 cm). Under the conditions described, rapid photobleaching of Methylene Blue is observed, which degrades the thermal lens signal with potentially serious consequences in terms of detection limits. The phenomenon has been studied and an empirical relationship developed to describe the behaviour of the thermal lens signal when photobleaching occurs.