Utilising Portable Laser-Induced Breakdown Spectroscopy for Quantitative Inorganic Water Testing

Abstract

At present, the majority of water testing is carried out in the laboratory, and portable field methods for the quantification of elements in natural waters remain to be established. In contrast, portable instruments like portable X-ray fluorescence (pXRF) analysis and portable laser-induced breakdown spectroscopy (pLIBS) have become routine analytical methods for the quantification of elements in solids. This study aims to show that pLIBS can also be used for chemical compositional measurements of natural waters. Bottled mineral waters were selected as sample materials. A surface-enhanced liquid-to-solid conversion technique was used to improve the detection limits and circumvent the physical limitations in liquid analysis. The results show that low to medium mineralised waters can be analysed quantitatively for their ions using the documented method. For more highly concentrated samples, typically above an electrical conductivity (EC) of 1000 µS/cm, further adjustment is required in the form of self-absorption correction. However, water with a conductivity up to this limit can be analysed for the main cations (Li+, Na+, Mg2+, K+, Ca2+, and Sr2+) as well as the main anions (SO42− and Cl−) using the documented method. This study demonstrates that there is significant potential for developing field-based pLIBS as a tool for quantitative water analysis.

Laser-Induced Breakdown Spectroscopy Applied to Elemental Analysis of Aqueous Solutions—A Comprehensive Review

“…Therefore, many different sample preparation techniques have been adapted and developed to bypass these issues. For example, liquid-to-aerosol conversion (LAC) [27], liquid-to-solid conversion (LSC) [11], and liquid jets (LJ) [28] can solve the problems by using a different sampling technique.…”

“…Tables 2-4). This is due to the variety of possible applications, ranging from basic research in laboratory analysis, typically using standoff or self-arranged LIBS [66], to remote analysis for hazardous substances, using telescopic systems [32], and to in situ analysis for environmental concerns using online [67] or portable instruments [11]. Therefore, both the LIBS setup and the sample preparation technique should be selected according to the desired application.…”

“…Here, too, the application plays a major role. For in situ measurements, higher LoDs are usually accepted if direct decisions can be made on the basis of the measured concentrations and if more detailed laboratory analyses are still possible afterwards [11]. Acquisition settings can either be a preset by the instrument or they can be set by the user.…”

“…The analysis of aqueous solutions for different elements is important for numerous reasons, such as environmental analysis [1], resource estimation [2], hydrogeochemical research questions [3], process control in nuclear fuel reprocessing plants [4], industrial control [5][6][7], food analysis [8], and medical applications [9]. Today, elemental analysis of aqueous solutions is typically performed in the laboratory using well-established methods such as ion chromatography (IC), atomic absorption spectroscopy (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and inductively coupled plasma mass spectrometry ICP-MS [10,11].…”

“…However, the analysis of aqueous solutions with LIBS, whether in the laboratory or in the field, has since played a rather niche role among potent and widely used analytical methods such as ICP-MS, ICP-AES, AAS, and IC [11]. This may be due to the complex interactions during the formation of the plasma at the surface of the liquid [10], or simply because the other methods have become so well-established that it has been difficult for LIBS to establish itself.…”