Stable Isotopic Labeling and Nontarget Identification of Nanogram/Liter Amino Contaminants in Water

Abstract

We report a new combinatorial approach of stable isotopic labeling (SIL)–solid phase extraction (SPE)–liquid chromatography–tandem high-resolution mass spectrometry (LC–HRMS/MS) for identification of amino-containing contaminants at trace levels in source water. The new SIL method requires small amounts of formaldehyde (CH2O) and deuterated formaldehyde (CD2O) to efficiently label ng/L amino compounds in 1 L of water and improves SPE recovery, enabling environmental analysis of trace amino-compounds. Isotopically methylated components were confirmed using LC–MS/MS based on their retention times, and characteristic isotope patterns of the molecular and product ions. Using the characteristic isotope patterns, we established a data prioritization process to identify the amino compounds in thousands of mass peaks in raw data. Analysis of a labeled authentic source water detected 8952 m/z peaks and tentatively identified 154 amino compounds. Our SIL-methylation prioritization approach effectively reduced the complexity of data. Manual spectrum interpretation identified 77 of the 154 components as amino acids and peptides. We confirmed 8 of the 77 compounds using commercially available standards to demonstrate the feasibility and reliability of our SIL–SPE–LC–HRMS/MS method for environmental analysis of trace amino-containing contaminants. The method can efficiently identify amino-precursors in source water, enabling other studies of nitrogenous disinfection byproduct formation.

Identification of N-Nitrosamines and Nitrogenous Heterocyclic Byproducts during Chloramination of Aromatic Secondary Amine Precursors

“…The in situ 14 N/ 15 N isotopic-pair labeling method facilitated deconvoluting the mass spectrum data and screening of N-DBP candidates Figure S1).…”

Nontargeted Identification of an N-Heterocyclic Compound in Source Water and Wastewater as a Precursor of Multiple Nitrosamines

“…Source water was used for labeling to identify potential N -DBP precursors. Source water was methylated using a previously reported method . Briefly, labeling reagents of aqueous CH 2 O (1.8 M), CD 2 O (1.8 M), and NaBH 3 CN (0.6 M) solutions were freshly prepared.…”

“…Various nitrogenous compounds can serve as precursors of nitrosamines under chloramination. The identified nitrosamine precursors include wastewater, polymers (e.g., polyDADMAC, polyamine, and anion exchangers), biofilters, pharmaceuticals, personal care products, and amino contaminants. − Recent nontargeted analysis of water has demonstrated a large number of highly water-soluble amine compounds in source water. , In general, amine contaminants exist at trace levels in source water and the majority are unidentified. , Nontargeted analysis can detect a massive number of compounds, but it is difficult to interpret the data . Thus, we have developed a stable isotope methyl labeling method that can effectively prioritize data corresponding to amino compounds in raw data.…”

“…Thus, we have developed a stable isotope methyl labeling method that can effectively prioritize data corresponding to amino compounds in raw data. This labeling-assisted nontargeted analysis can effectively identify amino acids and peptides present in source water . However, we encountered difficulty in identifying the other 77 unknown nitrogenous compounds detected by the isotopic labeling method due to the lack of database matches.…”

Noncovalently Tagged Gas Phase Complex Ions for Screening Unknown Contaminant Metabolites in Plants

“…The subsequent analysis of too many suspected features is an extremely time-consuming task. , Stable isotope labeling (SIL), i.e. introducing deuterated atoms or C 13 atoms into the parent compounds, has been proposed to provide additional structural information to exclude interfering species. ,− However, the isotopically labeled reagents are usually expensive and difficult to synthesize, which greatly constrains application of the SIL method. Therefore, the development of alternative methods that seek new structural characteristics for differentiating the metabolites from interfering species is still needed.…”