Fig. 6. (a) Contact resistance (R1), charge transfer resistance predominant at high frequencies (R2) and charge transfer resistance predominant at low frequencies (R3) as a function of ammonia concentration. Each data point reported is an average of at least 3 readings to ensure repeatability. The experimental data was well within the error limit of ±1.0%, the radii of the circles over each point adequately covering the errors. The squares of the correlation coefficients are presented for each fit in Table 1. (b) Capacitance predominant at high frequency (C1, pF) and low frequency (C1, µF) as a function of ammonia concentration. Each data point reported is an average of at least 3 readings to ensure repeatability. The experimental data was well within the error limit of ±1.0%, the radii of the circles over each point adequately covering the errors. The squares of the correlation coefficients are presented for each fit in Table 1.