Figure 1: Photograph and block diagram of prototype nitrite detection system. The sample is drawn either from a catheter or from a test tube, and then pumped through an ultrafiltration membrane, where the filtrate is extracted. The filtrate is then mixed with a solution of sulfuric acid and potassium iodide to reduce nitrite (NO2 -) to nitric oxide (NO). The nitric oxide is measured using an NO-specific electrode. Finally, the signal is sent to a PC for readout and signal processing.