Cellulose-based homogeneous method for suppressing coffee ring effect of cadmium detection in water using laser-induced breakdown spectroscopy

Abstract

Heavy metal pollution has a negative impact on water resources and poses a threat to crop safety and human health through biogeochemical cycles. To detect heavy metals in water, the dried droplet method (DDM) combined with laser-induced breakdown spectroscopy (LIBS) is commonly used. However, the uneven distribution of heavy metals caused by the coffee ring effect (CRE) can adversely affect the intensity and stability of the detection signal. In this study, the cellulose-based homogeneous method (CHM) was proposed to suppress CRE, ensure a uniform distribution of heavy metal (represented by Cadmium (Cd) in experiments) on the liquid-solid conversion deposition layer, and enhance the detection signal. A rapidly evaluated approach was developed using LIBS to visualize the homogeneity of Cd distribution on the deposition layer, which could also determine the type and concentration of cellulose. Furthermore, a comprehensive investigation of the mechanism was conducted from the perspective of fluid dynamics. The use of CHM resulted in a 94.81 % increase in signal average intensity and reduced the relative standard deviation (RSD) to 0.13 times. The R2 value achieved 0.997, and the limit of detection (LOD) reached 0.029 mg/L. CHM was validated using natural lake water samples spiked with a standard Cd solution resulting in a recovery rate ranging from 105.3 % to 109.06 %. The proposed method exhibits great potential to detect heavy metals in water resources, industrial wastewater, and agricultural water to assess water quality and water security.