Determination of Adsorbate Mass in Solution using QCM: Elimination of the Inseparable Liquid Contribution

Assumption-free mass quantification of (supra)molecular adsorbates in liquid environment remains a key challenge in many branches of material characterization and design. The quartz crystal microbalance (QCM) can uniquely determine the mass of essentially any adsorbed material; yet, when used in liquid environment, mass quantification is problematic since the surrounding liquid contributes significantly to the measured signal. Herein we show that the liquid contribution can be eliminated by measuring the QCM response in solutions with identical kinematic viscosities but different densities, making it possible to accurately quantify the dry mass of the adsorbed material. Furthermore, applying the same approach to the simultaneously measured energy dissipation enables quantification of the frictional losses associated with the attachment of the adsorbate. This straightforward and self-sufficient approach opens up new avenues in material characterization by enabling direct determination of the dry and wet mass, while simultaneously providing new insights into the mechanical properties of adsorbates.