Analytical Methods for Determination of ·NO and ·NO2 and their Applicability in Biological Studies

The biological and toxicological effects caused by nitric oxide and nitrogen dioxide, more commonly known as reactive nitrogen species (RNS), have increasingly stirred scientific curiosity about the molecular mechanisms of RNS activity in human body. These radicals possess certain characteristics that complicate their detection, namely their short lifetime and lack of specificity as they react with a variety of endogenous compounds present in biological samples. The development of reliable detection and quantification methods that are sensitive and specific is thus important. Today, nitric oxide can be detected and determined quantitatively by various analytical methods, such as colorimetry, spectrophotometry, electrochemistry, fluorescence, chemiluminescence, electron paramagnetic resonance, gas and liquid chromatography, electrophoresis and mass spectrometry. On the other hand, there are only a few methods capable of measuring nitrogen dioxide. The aim of the present article is to give an overview of the commonly used analytical methods for measuring ·NO and ·NO2 in biological systems. The underlying mechanisms and principles of these methods are discussed.