N-Nitrosopiperazines form at high pH in post-combustion capture solutions containing piperazine: a low-energy collisional behaviour study

During the process of exploring aqueous piperazine chemistry under simulated flue‐gas scrubbing conditions, positive‐ion electrospray ionisation mass spectrometric (ESI‐MS) analyses of the resulting reaction mixtures in a triple quadrupole system revealed the presence of peaks at m/z 116 and 145, the putative N‐nitroso derivatives of piperazine. Confirmation of the presence of these species in the reaction mixtures was achieved using collision‐induced dissociation experiments. A purchased standard, together with in‐house synthesised N‐nitrosopiperazine standards (including N‐nitroso derivatives derived from deuterium‐labelled precursor materials), were used for this purpose. Across a small range of collision energies, large fluctuations in the abundance of the two major product ions of protonated N‐nitrosopiperazine, m/z 86 and 85, were observed. Using B3LYP/6‐311 + +G(d,p) computations, the potential energy surface was determined for loss of NO and H,N,O]. At an activation energy slightly in excess of 1 eV, intramolecular isomerisation precedes loss of NO (m/z 86) via a 4,1 H‐shift, and at activation energies between 2.1–2.3 eV, consecutive loss of NO and atomic hydrogen competes with the direct loss of nitrosyl hydride (m/z 85). It is recommended that any multiple reaction monitoring method for quantifying N‐nitrosopiperazines at low collision energies use the sum of both transitions (m/z 116 ← 85, m/z 116 ← 86) to avoid errors that could be introduced by subtle changes in ES source conditions or collision voltages. This approach is adopted in an HPLC/MS/MS method used to monitor the degradation of N‐nitrosopiperazine exposed to (i) broad‐band UV light and (ii) heat typical of an amine regeneration (stripper) tower. The results reveal that aqueous N‐nitrosopiperazine is thermally stable at 150°C but will degrade slowly upon exposure to UV light. Copyright © 2010 John Wiley & Sons, Ltd.