Polyethylene Glycol-Assisted Suppression of the Coffee-Ring Effect for Improved Quantitative Performance in Dried-Droplet Laser-Induced Breakdown Spectroscopy

Fast detection of trace heavy metals in aqueous media using the laser-induced breakdown spectroscopy (LIBS) technique is of critical importance because of their potential environmental and health risks. Among various strategies for liquid LIBS analysis, the dried droplet method has been widely adopted. However, the coffee-ring effect (CRE) remains a major obstacle to uniform LIBS signal distribution and accurate quantification of target elements. This work proposes a simple and rapid pretreatment strategy to control the deposition morphology of droplets on graphite substrates by adding polyethylene glycol 400 (PEG 400) to suppress the CRE. Experiments demonstrate that adding a PEG 400 mass fraction of 0.5% significantly improves deposition uniformity. Based on this optimized method, LIBS determination of trace cobalt (Co) and strontium (Sr) achieved limits of detection (LODs) of 1.46 and 0.091 mg/L, respectively. Compared to the PEG 400-free condition, the LODs improved by factors of 3.05 for Co and 2.42 for Sr, while the average relative standard deviations decreased from 38.74% to 9.04% for Co and from 32.58% to 10.47% for Sr. These results demonstrate that PEG 400-assisted modulation of droplet evaporation effectively suppresses the CRE, enhancing LIBS-based detection performance for trace metals in aqueous media. The strategy offers a viable solution for environmental monitoring and rapid analysis of industrial effluents.