Simple and Equipment-Free Paper-Based Device for Determination of Mercury in Contaminated Soil

• Main Authors: Hikmanita Lisan Nashukha, Jirayu Sitanurak, Hermin Sulistyarti, Duangjai Nacapricha, Kanchana Uraisin
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Molecules
• Subjects: tetraiodomercurate; mercury; paper-based; iodometry; soil; water
• Online Access: https://www.mdpi.com/1420-3049/26/7/2004

This work presents a simple and innovative protocol employing a microfluidic paper-based analytical device (µPAD) for equipment-free determination of mercury. In this method, mercury (II) forms an ionic-association complex of tetraiodomercurate (II) ion (HgI₄²⁻_(aq)) using a known excess amount of iodide. The residual iodide flows by capillary action into a second region of the paper where it is converted to iodine by pre-deposited iodate to liberate I_2(g) under acidic condition. Iodine vapor diffuses across the spacer region of the µPAD to form a purple colored of tri-iodide starch complex in a detection zone located in a separate layer of the µPAD. The digital image of the complex is analyzed using ImageJ software. The method has a linear calibration range of 50–350 mg L⁻¹ Hg with the detection limit of 20 mg L⁻¹. The method was successfully applied to the determination of mercury in contaminated soil and water samples which the results agreed well with the ICP-MS method. Three soil samples were highly contaminated with mercury above the acceptable WHO limits (0.05 mg kg⁻¹). To the best of our knowledge, this is the first colorimetric µPAD method that is applicable for soil samples including mercury contaminated soils from gold mining areas.