Influence of electrolytes in the QCM response: Discrimination and quantification of the interference to correct microgravimetric data

In this work we demonstrate that the presence of electrolytes in solution generates desorption-like transients when the resonance frequency is measured. Using impedance spectroscopy analysis and Butterworth–Van Dyke (BVD) equivalent electrical circuit modeling we demonstrate that non-Kanazawa responses are obtained in the presence of electrolytes mainly due to the formation of a diffuse electric double layer (DDL) at the sensor surface, which also causes a capacitor like signal. We extend the BVD equivalent circuit by including additional parallel capacitances in order to account for such capacitor like signal. Interfering signals from electrolytes and DDL perturbations were this way discriminated. We further quantified as 8.0 ± 0.5 Hz pF−1 the influence of electrolytes to the sensor resonance frequency and we used this factor to correct the data obtained by frequency counting measurements. The applicability of this approach is demonstrated by the detection of oligonucleotide sequences. After applying the corrective factor to the frequency counting data, the mass contribution to the sensor signal yields identical values when estimated by impedance analysis and frequency counting.