Summary of some relevant works on indirect HNO detection.

Detection	Trapping system	Advantages	Disadvantages
UV-Vis	Mn-porphyrin in a protein matrix159	+ Air stable	− Limited application in biological samples due to UV Soret band interference
		+ Good sensitivity (low nM level)
		+ HNO/NO discrimination
UV-Vis	Mn-porphyrin in a xerogel160	+ Air stable	− Limited application in biological samples due to UV Soret band interference
		+ Good sensitivity (low nM level)	− Cannot be reused due to gel aging
		+ HNO/NO discrimination
HPLC-UV	Thiol (glutathione)166	+ HNO/NO discrimination	− Requires previous purification
		+ Good sensitivity (low μM level)	− Formation of GSSG may interfere
		+ Can be applied to biological samples
UV-Vis	Phosphine carbamates169	+ Good sensitivity (low μM level)	− Limited application in biological samples due to phosphine hydrolysis
		+ HNO/NO discrimination
EPR	Liposome-encapsulated nitronyl nitroxides172	+ Potential compatibility with biological samples (no experiments have been carried out to date)	− Requires special and expensive equipment, which is not always readily available
		+ HNO/NO discrimination