Porous-polymer monolith decorated with dithizone for greener visual and spectrophotometric sensing of Hg(II)

This paper describes a hydrophobic porous polymer monolith for visual and spectrophotometric determination of Hg(II). The monolith was synthesized in the coffins of 2.0 mm i.d. transparent polypropylene ink-pen tubes using stearyl methacrylate (SMA) as the functional monomer and ethylene glycol dimethacrylate (EDMA) as the crosslinker by fast UV-mediated polymerization. The poly(SMA-co-EDMA) monolith retained dithizone, an anchor for the Hg(II) and colorimetric reagent. Besides the monolith's fast preparation, the polypropylene transparency enabled the naked-eye visualization of all color changes occurring in the solid phase extraction steps (conditioning, loading, washing and elution). This feature also enabled the unprecedented use of a simple ruler for detection since the distance occupied by Hg(II) inside the column was linearly related to Hg(II) concentration. Loading the column with 12.0 mL of sample and elution with 1.0 mL of ethanol contributed to the green analytical chemistry and provided a detection limit of 7.9 µg L−1, which was enough to determine Hg(II) in certified estuarine sediment (ERM-CC580) and urine samples. A sample volume of 45 mL provides a detection limit of 0.59 μg L−1, allowing the detection of trace Hg(II) levels in the Billings reservoir waters, an anthropized water reservoir located in the São Paulo Metropolitan Area of São Paulo State (Brazil), thus attending the maximum concentration levels preconized by the United States Environmental Protection Agency (1.0 µg L−1) and World Health Organization (6.0 µg L−1). The proposed method is simple, cheap and can be easily implemented in field measurements for sample trials.