Handling and Detection of Nitric Oxide

Solubility of nitric oxide in water as a function of temperature (Seidell, 1919). 

Nitrite and nitrate may also be determined by HPLC using anion-exchange columns with either UV absorption or electrochemical detection. These methods are generally used for environmental samples and urine where fewer interfering compounds exist. The more extensive sample preparation and analysis time have limited its use for biological samples. 

Nitric oxide release from blood vessels was first detected by chemiluminescence (Palmer et ai, 1987). In the original adaptations of the nitric oxide detector, perfusates from isolated vessels were directly mixed in a reflux chamber containing acetic acid and iodine. The iodine in the reflux chamber served to reduce any nitrites or nitroso-containing groups to nitric oxide, which was stripped from the chamber by a continuous stream of nitrogen or helium that flowed to the chemiluminescent detector. Replacement of the acetic acid with the less volatile trichloroacetic acid reduces problems with contamination of the nitric oxide detector (Dr. D. Harrison, Emory University, Atlanta, Georgia, personal communication, 1991). While extremely sensitive, the use of the acid reflux chamber also reduces the specificity of the assay, raising questions as to whether nitric oxide or a nitrosothiol is EDRF (Myers et ai, 1990). 

Measurement of nitric oxide by absorption into hydrophobic tubing. The apparent disappearance of nitric oxide is due to uptake into the hydrophobic tubing and is independent of the oxygen concentration in the solution. Peroxynitrite (ONOO ) rapidly destroys nitric oxide as shown by the rapid decrease in the signal. The details of the basic apparatus are shown in Fig. 18. 

Nitric oxide can be assayed directly in tissues by its electrochemical oxidation on electrode surfaces (Shibuki, 1990). The technique was successfully used by Shibuki in cerebellar slices. However, the probe was fabricated in a glass micropipet coated with a thin hydrophobic chloroneoprene membrane, which makes the technique experimentally difficult. More recently, a carbon fiber electrode 

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