Detection and binding interactions of pharmaceutical contaminants using quartz crystal microbalance - Role of adsorbate structure and surface functional group on adsorption.

HYPOTHESIS

Emerging contaminants (ECs) can interact with soft solid/aqueous interfaces of particulate organic matter and microplastics in the aquatic environment but to what extent? It is hypothesized that EC adsorption can be detected using quartz crystal microbalance (QCM), a sensitive gravimetric tool, and their adsorption energetics and uptake capacity can be measured for various substrates of distinct functional group. This in turn reveals the specific vs. nonspecific interactions.

EXPERIMENTS

QCM has been used to detect and measure the adsorption of selected pharmaceuticals, amlodipine (AMP) and carbamazepine (CBZ), onto butyl, carboxyl, amine, and phenyl functionalized self-assembled monolayers (SAMs), mapping out the hydrophobic effect, H-bonding capability, and π- interactions. Adsorption free energy (ΔG) and maximum interfacial concentration (c) for these surfaces are compared. Solvatochromic studies to elucidate the likelihood of H-bonding interactions for CBZ and AMP have been conducted using UV-Vis absorption spectroscopy.

FINDINGS

Amlodipine and carbamazepine adsorb onto butyl/aqueous interface with respective ΔG values of -35.8 ± 1.1 and -37.7 ± 0.1 kJ/mol. Nonspecific interaction allows a greater extent of c on the hydrophobic/aqueous interface. CBZ does not bind to the phenyl surface. AMP and CBZ exhibit H-bonding and show proclivity for the amine and carboxyl SAMs. Interfacial chemical environment and adsorbate structural properties play a significant role on EC adsorption.