Improvement of the sensitivity for the measurement of copper concentrations in soil by microwave-assisted laser-induced breakdown spectroscopy

a r t i c l e i n f o This study shows a 23-fold improvement of the sensitivity in the determination of copper in soil samples when using Microwave-Assisted Laser-Induced Breakdown Spectroscopy (MA-LIBS) compared with our conventional LIBS. This comparison between MA-LIBS and LIBS was performed with identical ablation conditions and detection geometry. The signal enhancement obtained with MA-LIBS allowed for the detection of spectral lines related to concentration values as low as 30 mg kg −1 for copper and 23.3 mg kg −1 for silver, which were not detected by LIBS. The monitoring of concentration of metallic elements in soil is of great importance to environmental research, agriculture, and public health [1–3]. Mobile toxic metals in the soil (Cu, Pb, Cd, Cr, …) can accumulate in the human body through the food chain [3,4] or prolonged exposure to trace amounts of contaminated aerosols [5]. The so-called-heavy metals in the soil, whether naturally concentrated or from the discharge of industrial or civilian waste, are harmful to the health of human beings, animals and plants. Overdose of metal salts (Na, Ca, and Mg) in the soil results in salinization [1], which can reduce the productivity of farmland and have serious consequences on food production. An element of interest is copper. The copper concentration in soil determines if it should be considered as a nutrient for plants or a toxic metallic pollutant. As a nutrient, copper is absorbed by plants and involved in photosynthesis and respiration [6]. However, a high concentration of copper can lead to growth reduction and other issues [7]. For human beings , both copper deficiency and excess can cause health problems [8]. For ecological preservation, 61 mg kg −1 is set as the soil screening level (SSL) for copper by the Environmental Protection Agency (EPA), which is the level that triggers further ecological risk assessment [9]. Major environmental hazards can be contained or prevented by monitoring the elemental composition of the soil. With the data obtained, necessary warnings can be given and remedial action can be taken. Laser-induced breakdown spectroscopy (LIBS) is a technique attracting increasing attention from both researchers and end-users for environmental monitoring. In LIBS, focused laser radiation is used to ablate and excite the sample material simultaneously. The plasma created from the sample material provides elemental information about the sample via the optical emission [10,11]. Compared with several elemental analysis methods for environmental …