Ehrenstorfer (Ausburg, Germany). The internal standards N-nitrosodimethylamine-d6 (NDMA-d6) and N-nitrosopyrrolidine-d8 (NPYR-d8) were purchased from Sigma–Aldrich Co. and CDN Isotopes (Quebec, Canada), respectively.
Ehrenstorfer (Ausburg,Germany). The internal standards N-nitrosodimethylamine-d6(NDMA-d6) and N-nitrosopyrrolidine-d8 (NPYR-d8) were purchasedfrom Sigma–Aldrich Co. and CDN Isotopes (Quebec, Canada),respectively.