Use of ISO-NOP200 for measurement of NO in the gas phase under controlled humidity conditions

A technique has been developed to measure nitric oxide (NO) in the gas phase using the ISO-NOP200 NO-specific probe, which was designed to only measure NO in solution. It was found that probe output was responsive to the relative humidity (RH) of the atmosphere. Increasing sensitivity of probe output to NO was observed with increasing RH but the time to achieve a stable output was also increased. The recommended method to give high sensitivity but an acceptable time between analyses was to hold the probe at a constant temperature (20 degreesC) in a sealed 20 ml glass vial containing 4 ml of a saturated solution of NaCl, which provides a constant RH of 75%. NO standards and samples were injected directly into the vial and provided good baseline stability and a limit of detection of 0.18 mul/L in the vial. The limit of detection of the analytical sample will depend on the volume of gas injected into the vial. Up to 4 ml could be injected without disturbing probe stability and this equates to a detection limit of 0.75 mul/L NO. However, analysis of the internal atmosphere of banana fruit could only consistently extract 1 ml of gas, which gave a detection limit of 3 mul/L NO. (C) 2003 Elsevier Inc. All rights reserved.