To improve the unique fingerprints from each AA, we also considered the dependence of CT on pH. While Ψo depends mainly on the distribution of charges between the double layer capacitance and the AA themselves, CT depends also on the dielectric constant and thickness of the AAs, which are orthogonal properties to the charge. CT can be derived with electrical impedance spectroscopy from the FET transconductance at variable frequencies. The effective electrolyte-gate capacitance is comprised of the different contributions in series: (i) a device capacitance, (ii) AA/peptide capacitance, and (iii) the double layer capacitance. As the double-layer capacitance also depends on the different pK of the AAs, CT also exhibits unique features that will depend on the pH. Due to the elimination of the double layer capacitance, the isoelectric point will be observed as a minimum in the CT vs pH. The values of those minima can be normalized to the NS derived from the linear part of Ψo. The normalized CT minima are associated with the length and the dielectric constant of each neutral peptide, establishing the second orthogonal signature (fingerprint) of each AA, which can be considered together with the pH behavior as the CT vs pH or its derivative that exhibit similar singularity to the case of Ψo. and D compared to its expression in Ψo. While C exhibits a very linear behavior and the isoelectric point is less apparent in Ψo, the shape of the minimum is well defined in CT. Instead, for D, while the isoelectric point in Ψo is more apparent, CT shows a broader less resolved minimum. The results reveal that the higher away capacitances from the isoelectric point for D and C are due to the charge stored in the electrical double layer but the capacitance for R and A keeps on decreasing with an increase in pH due to saturation of deprotonated amine-reactive sites. Considering the normalization to NS in the range of 10 10 groups/cm 2 (accessible in experimental conditions ), the normalized capacitance requires a resolution of 10 μF to identify the AAs, which is a well achievable measurable quantity. Considering a FET gate of 1 μm 2 , also easily attainable for current microfabrication techniques, this signal would correspond to an average of 100 molecules, which is largely improving the state of the art for MS (~10,000 molecules needed for ex-novo sequencing). A higher-order capacitance gradient with respect to pH can pinpoint the pK values as zero-crossover points with stored charge transition from positive to negative. We can use our approach to iteratively solve the surface potential with self-consistency convergence for precise calculation of the active surface states (NS)/dissociation constants and have a full characterization of the peptide interphase which can be compared with the experiments. the capacitance minima. Hence, it can be concluded that capacitance curves can be used in combination with the surface potential data or independently to characterize each AA. However, a few of the intracategory AAs have a lower capacitance resolution of 0.01mF/m 2 with similar CT minima for Leucine and Isoleucine, due to their difference in length that occurs because of the different relative positions of the carboxylic and amino groups. This calculation is an approximation since we do not consider the changes in pK values that occur after immobilization, but assuming the value, which could be changed after a phenomenological adjustment of the values, thus the change in capacitance would allow distinguishing two isomers that cannot be resolved by current MS methods. Our model also neglects the 3D effect of the position of the charges, which would increase the differences between molecules, in particular considering that each radical would have differences in the local screening.