Photothermal lens spectrometry: Experimental optimization and direct quantification of permanganate in water

Abstract

• An optimization of Thermal Lens Spectrometry (TLS) experiment was made. • The TLS method is appropriate for permanganate quantification in water treatment application at neutral pH. • The Limits of Detection are 0.22 μM and 0.08 μM for distilled and tap water, respectively. Although permanganate is a widely used oxidant in drinking water and wastewater treatment, only few spectrometric methods were proposed for measuring its concentration in water. The thermal lensing spectrometry (TLS) experiment was optimized and applied for the quantification of trace permanganate in water at neutral pH. Several parameters (probe beam waist position, confocal parameters and detector position) influencing the thermal lens (TL) signal were explored in order to optimize the geometry of mode-mismatched dual-beam experiment. Based on the obtained experimental and theoretical results, the TL signal reaches an amplitude that is two times larger than that obtained with the collimated method. As application of this experiment, I have measured the limit of detection (LOD) and quantification (LOQ) of permanganate in distilled and tap water without the need of reagents. The obtained results of LOD are 0.22 μM and 0.08 μM for distilled and tap water, respectively. These values are better than those obtained by the conventional absorption spectrometry method which is suitable for samples containing more than around 5.5 μM, and close to the LOD achieved by indirect spectrometric methods.