Stability improvement for dried droplet pretreatment by suppression of coffee ring effect using electrochemical anodized
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ORIGINAL PAPER
Stability improvement for dried droplet pretreatment by suppression of coffee ring effect using electrochemical anodized nanoporous tin dioxide substrate Yuanchao Liu 1 & Jie Pan 2 & Zhenlin Hu 3 & Yanwu Chu 3 & Muhammad Shehzad Khan 1 & Kaiwei Tang 1 & Lianbo Guo 3 & Condon Lau 1 Received: 27 August 2020 / Accepted: 9 November 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract A novel nanoporous analytical platform is reported to improve the stability of the dried droplet method (DDM). This nanoporous platform was made of tin dioxide (Np SnO2) substrate by electrochemical anodization from tin (Sn) slide. The DDM is a widely used sample pretreatment in analytical chemistry that involves placing a droplet of solution onto the substrate and drying for analytical testing. However, during the droplet drying process, the solutes would converge at the droplet edge and cause inhomogeneous solutes distribution. This is the coffee ring effect (CRE). The Np SnO2 has irregular nanopores, which allows droplet solutions to penetrate into the substrate rather than spreading out, effectively suppressing CRE. Theoretical models were built to explain the formation of CRE on blank tin (Sn) substrate and suppression of CRE on Np SnO2. Better results were obtained in detecting lithium (Li) using the Np SnO2 by laser-induced breakdown spectroscopy (LIBS). The line scanning results indicated that the Li emission line (670.8 nm) intensities on Np SnO2 substrate had lower relative standard deviation (RSD = 3.3%) than those on Sn substrate (RSD = 31.5%), which illustrate suppression of CRE and stability improvement on Np SnO2 substrate. Furthermore, Li calibration curves were built for LIBS with DDM. The curve using Np SnO2 substrate had better linearity (R2 = 0.997), higher precision (RSD = 4.2%), and higher sensitivity (LOD = 0.13 mg/L) than that by Sn substrate (R2 = 0.954, RSD = 17%, and LOD = 1.21 mg/L). All in all, the anodic Np SnO2 substrate can suppress CRE in DDM and hence improve the stability and precision of subsequent analysis. Keywords Dried droplet method . Coffee ring effect . Electrochemical anodized nanoporous tin dioxide substrate . Laser-induced breakdown spectroscopy (LIBS)
Introduction The dried droplet method (DDM) is a widely used sample pretreatment method in analytical chemistry [1, 2]. The basic
* Lianbo Guo [email protected] * Condon Lau [email protected] 1
Department of Physics, City University of Hong Kong, Hong Kong SAR, China
2
Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, China
3
Wuhan National Laboratory for Optoelectronics (WNLO), Huazhong University of Science and Technology, Wuhan 430074, Hubei, China
process is transforming solid samples to solution, dropping the solution onto the substrate, and drying. DDM has many advantages [3, 4], which include less sample consumption and matrix effect reduction. Therefore, DDM has been applied in analytical methods such as surface-enhanced Raman spectroscopy (SE
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