Sustainable and reagent-free mercury trace determination in natural waters using nanogold dipsticks

Abstract

Determination of mercury traces in the hydrosphere is an important and still challenging analytical task. Here we report on a novel solid phase extraction (SPE) method for total dissolved mercury (Hg) determination in natural waters using newly developed nanogold-coated dipsticks. Straightforward preparation of the dipsticks comprises golf film deposition onto glass substrates modified with APTMS-coated non-porous silica particles (ø = 300 nm). Subsequent annealing process leads to an immobilized gold nanoparticle (AuNP) layer on the surface of the flat sampling sticks, which was characterized in detail by electron microscopy. For selective Hg accumulation into this active AuNP layer, the dipstick is immersed in the water sample for a few seconds up to 10 min depending on the concentration range of the sample and desired sensitivity. After thermal desorption of Hg from the sticks subsequent quantification by atomic fluorescence spectroscopy (AFS) is performed. Several parameters for SPE like duration, temperature, turbulent and stagnant conditions, as well as heating duration for Hg release were investigated and optimized. The limit of detection was found to be as low as 0.18 ng Hg L−1 for 10 min extraction duration and calculated to be 10 ng L−1 for a dipping time of only 10 s. High reproducibility with relative standard deviations ≤4.9% (n = 3) is given. In addition, high repeatability and low batch-to-batch variation for individually prepared dipsticks confirm feasibility of the approach. The validity of the optimized approach was confirmed by successful recovery experiments in real seawater (R = 105%), river water (R = 98%) and the certified reference material ERM-CA400 (seawater; R = 94%).