Basics of utilizing NH ${}_4^{+}$ ions for accurate phthalate ester quantification via selected ion flow tube mass spectrometry in food

Phthalate esters, frequently used as plasticizers in consumer products, raise concerns because of potential health effects. Using density functional theory (DFT) with B₃LYP and 6-311++G(d, p) basis sets, their properties, such as dipole moment, polarizability, proton affinity and ionization energy of phthalate esters are obtained. Reaction kinetics and thermodynamics of popular reagent ions like H₃O${}^{+}$, NH${}_4^{+}$, NO${}^{+}$ and O${}_2^{+}{}^{\bullet }$ are computed to know the feasibility of the reactions with such ions. Proton affinity and ionization energy indicate high susceptibility to proton and charge transfer reactions. High dipole moments contribute to elevated rate coefficients in proton transfer reaction mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry (SIFT-MS). PTR-MS rates are influenced by drift tube conditions, supported by high center-of-mass collisional energy of E${}_{\mathrm{cm}}$ = 0.28 eV. SIFT-MS rates diminish with rising temperature. The high kinetic energy data of H₃O${}^{+}$, NO${}^{+}$ and O${}_2^{+}{}^{\bullet }$ suggests that simple proton transfer and charge transfer reactions are overruled due to very high internal energy which could lead to extensive fragmentation of phthalate esters. The energetic profile of NH${}_4^{+}$ ions indicates their suitability for quantifying phthalate esters using NH${}_4^{+}$-CI-MS techniques.