Previous studies of OMIECs have employed electrochemical quartz crystal microbalance (EQCM) to capture mass/thickness changes. Microbalance techniques cannot differentiate between species that contribute to thin film mass changes, thus some studies reporting dopant and solvent concentrations depend on the assumption that counter ion contributions are excluded, though others have found evidence indicating counter ion contributions. Recent work has employed X-ray photoelectron spectroscopy (XPS) and glow discharge optical emission spectroscopy (GDOES) to quantify the composition of OMIECs. These studies have monitored the passive (not driven by applied potential) uptake of anion-cation pairs, the competition of cation expulsion and anion injection in the electrochemical p-doping processes, and the ion trapping that enables non-volatile electrochemical state retention. These reports give important insights into the fundamental processes in OMIECs. However, they are hindered by high detection limits and difficulties with calibration that constrain them to reporting qualitative results. Thus, quantitative composition determination in OMIECs remains to be achieved.