Nitrite ion mitigates the formation of <i>N</i>-nitrosodimethylamine (NDMA) during chloramination of ranitidine

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Ranitidine (RNT) has been an important tertiary amine precursor of <I>N</I>-nitrosodimethylamine (NDMA) in chlorine-based water treatment, due to reaction with monochloramine (NH<SUB>2</SUB>Cl) with exceptionally high molar yields up to 90%. This study examined the effects of nitrite ions (NO<SUB>2</SUB> <SUP>−</SUP>) on the kinetics of NDMA formation during the chloramination of RNT under variable concentrations of dissolved oxygen (DO, 0.7–7.5mg/L), RNT (5–30μM), NH<SUB>2</SUB>Cl (5–20mM), NO<SUB>2</SUB> <SUP>−</SUP> or NO<SUB>3</SUB> <SUP>−</SUP> (0–2mM) and pH (5.6–8.6). In the absence of the NO<SUB>2</SUB> <SUP>−</SUP>, the ultimate molar yield of NDMA after 6h of reaction was primarily influenced by [DO] and pH, while marginally affected by initial [RNT] and [NH<SUB>2</SUB>Cl]. A kinetic model, prepared in accordance with the reaction sequence of NDMA formation, suggested that the rate determining step was accelerated with increasing [NH<SUB>2</SUB>Cl]<SUB>0</SUB>, [DO], and pH. A Kinetic study together with ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometer (UPLC-Q-TOF MS) and gas chromatography (GC)/TOF MS analyses in parallel demonstrated that the nitrite ion inhibited the nucleophilic substitution of the terminal amine on NH<SUB>2</SUB>Cl, and reduced the pseudo-steady state concentration of <I>N</I>-peroxyl radicals, significantly decreasing the ultimate yields of NDMA.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nitrite ion inhibited NDMA formation during chloramination of ranitidine. </LI> <LI> DO, pH, and initial substrate concentrations also affected the molar yield. </LI> <LI> A three-parameter kinetic model was proposed based on NDMA formation pathway. </LI> <LI> Nitrite ion changed the specification of nitrosating agents. </LI> <LI> Nitrite ion interacted with <I>N</I>-proxy radicals. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>