Exchange of 18O in the reaction of peroxynitrite with CO2

We have observed an exchange of 18O in the reactions of CO2 with peroxynitrite using membrane-inlet mass spectrometry and HPLC negative electrospray ionization mass spectrometry. The exchange appeared on addition of peroxynitrite to a solution containing 18O-labeled CO2 in equilibrium with bicarbonate. It was observed as a temporarily enhanced rate of depletion of 18O from CO2, a rate that was greater than the rate of 18O depletion caused by the hydration/dehydration cycle of CO2. In addition, we detected the appearance of mass peaks attributed to 18O in product NO3-.As a further measure of the 18O exchange, there was a redistribution of 18O such that the ratio of doubly to singly labeled CO2 could not be described by the binomial expansion. This is not due to the hydration/dehydration cycle of CO2 but most likely to recycling of CO2 in the reaction with peroxynitrite. This 18O exchange associated with the reactions of CO2 and peroxynitrite may open a new methodology for studying this significant process.