The present disclosure relates to an ion exchange process, as well as a process and system for detecting nitrates, which employ a class of dopants comprising at least two functional groups capable of simultaneous convergent hydrogen bonding with a nitrate ion. In an aspect, the present disclosure provides an ion exchange process for forming a negatively charged nitrate-dopant ion analyte for analysis by a spectrometry analysis instrument, comprising: providing a gas comprising a dopant in both neutral and ionized forms; contacting a nitrate-containing sample with the gas comprising the dopant and thereby desorbing a nitrate ion from the sample to form a negatively charged nitrate-dopant ion analyte and replacing the desorbed nitrate ion with a negatively charged ionized dopant molecule; wherein the dopant is an organic compound comprising two or more carbon atoms and two or more functional groups capable of simultaneous convergent hydrogen bonding with a nitrate ion; or the dopant is an organic compound comprising at least two carbon atoms and only a single functional group capable of hydrogen bonding with a nitrate ion, which group is a —COOH functional group, and where the carbon atom of the —COOH functional group is bonded directly to another carbonyl group; and with the proviso that the dopant is not lactic acid, a lactic acid salt or a compound that forms lactate ions upon ionization.