Measuring the diffusion coefficient measurement of TEMPO was performed by connecting a switching valve, syringe pump, temperature probe, and potentiostat. 400 random combinations of scan rates ranging from 10 mV/s to 1 V/s and analyte concentrations ranging from 0.1 mM to 6 mM were generated, as seen in the inset of Fig 3c . A solution of 6 mM TEMPO in 0.1 M bicarbonate buffer was mixed with a solution of 0.1 M bicarbonate buffer to achieve the desired concentration. The different concentrations were dispensed in random orders, and CVs were performed at all corresponding scan rates for each concentration. The cell was flushed with water and primed before changing concentrations, which was determined to be appropriate upon evaluating three different cleaning protocols to assess sample carryover between experiments (Supplementary Note S5 and Table ). We measured a reference-adjusted E1/2 of 0.78 V ± 0.01 V vs. SHE, in line with the reported literature value of 0.75 V vs. SHE (Figure ). Diffusion coefficients were calculated using the Randles-Ševčík equation with baseline-subtracted peak currents (Supplementary Note S6 and Figures ), and the resulting distribution is shown in Figure . The mean diffusion coefficient was determined to be 6 × 10 -6 cm 2 /s, which is in good agreement with previously reported values, but the resulting distribution had a large standard deviation of ± 2 × 10 -6 cm 2 /s. We have seen in our previous work that large distributions of diffusion coefficient measurements are often skewed by inaccurate concentration volumes that result from dispensing errors, as may be the case here. We see that the largest outliers in the distribution are from experiments where less than 200 µL of analyte were dispensed (Figure ).