Calibration of NO sensors for In Vivo Voltammetry: Laboratory synthesis of NO and the use of UV-visible spectroscopy in determining stock concentrations

The increasing scientific interest in nitric oxide (NO) necessitates the development of novel and simple methods of synthesising NO on a laboratory scale. In this study we have refined and developed a method of NO synthesis, using the neutral Griess reagent, which is inexpensive, simple to perform, and provides a reliable method of generating NO gas for in-vivo sensor calibration. The concentration of the generated NO stock solution was determined using UV–visible spectroscopy to be 0.28±0.01 mmol L−1. The level of NO2− contaminant, also determined using spectroscopy, was found to be 0.67±0.21 mmol L−1. However, this is not sufficient to cause any considerable increase in oxidation current when the NO stock solution is used for electrochemical sensor calibration over physiologically relevant concentrations; the NO sensitivity of bare Pt-disk electrodes operating at +900 mV (vs. SCE) was 1.08 nA μmol−1 L, while that for NO2− was 5.9×10−3 nA μmol−1 L. The stability of the NO stock solution was also monitored for up to 2 h after synthesis and 30 min was found to be the time limit within which calibrations should be performed