Differential pulse voltammograms for an iodine coated electrode in 0.1 M PBS (pH 7) of spiked with (A) spiked with urine sample only (B) spiked with 20 µl of dopamine (C) spike with 40 µl of dopamine. Scan rate = 5 mV s-1, modulation amplitude = 50 mV, pulse repeat time = 1 s.