Less is more: how reducing the ablation atmosphere pressure can boost sensitivity for fluorine in laser-induced breakdown spectroscopy

Abstract

Laser-induced breakdown spectroscopy (LIBS) is a rapid and minimally destructive technique which enables measurement of almost every element of the periodic table. However, fluorine determination remains challenging due to low sensitivity and weak emission signals. In this work, the influence of reduced ablation atmosphere pressure on fluorine detection by LIBS is systematically investigated, including parameter optimization steps for gate delay and laser energy. A significant increase in fluorine signal intensity was observed with decreasing pressure. The impact of pressure on signal stability, calibration behaviour, and limits of detection was assessed and compared to measurements at atmospheric pressure. In that regard, different evaluation approaches, including univariate and multivariate models (using Partial Least Squares) were considered. The results demonstrate that reduced-pressure conditions lead to improved sensitivity and lower limits of detection, enabling more reliable fluorine quantification. For the univariate calibration models, sensitivity was approx. double at 50 mbar compared to atmospheric pressure, while the limit of detection reduced from 505 to 104 µg g⁻¹. Further, sensitivity in the multivariate models improved by up to 80% leading to a decreased limit of detection of 121 µg g⁻¹ at 50 mbar in comparison to 286 µg g⁻¹ at atmospheric pressure. The findings presented here show that controlling the ambient pressure is an effective strategy to enhance fluorine detection by LIBS without requiring extensive sample preparation or major instrumental modifications. This approach broadens the applicability of LIBS for the direct analysis of fluorine in solid samples and provides a practical route to improved analytical performance.