Effect of the lens-to-target distance on the determination of Cr in water by the electro-deposition method and laser-induced breakdown spectroscopy

Abstract

This paper studied the effect of the lens-to-target distance (LTTD) on determining Cr in water by laser-induced breakdown spectroscopy and the electro-deposition (ED) method. First, the metal ED method realized the solid-state transformation of Cr in water. Then, a focusing lens (with a focal length of 100 mm) was used to study the influence of the LTTD on the qualitative and quantitative analysis of Cr in water. The results showed that changing the LTTD can result in optimized emission intensity of Cr(I), and the position for the Cr(I) emission maximum was different from the position for the continuous emission maximum. The LTTD for the Cr(I) emission maximum was far from the focal point (−68 mm), while the LTTD for the continuous emission maximum was near the focal point (−90 mm). For quantitative analysis, the limit of detection (LOD) maintained a lower value in the LTTD range from −74 mm to −58 mm, and the LOD at −68 mm was the best. The experimental results showed that the traditional optimization result of the LTTD (the position for the strongest spectral emission is near the focal point of the focusing lens) is not suitable for substances (to be detected) that only exist on the surface of a metal substrate.