Milli q integral water puri cation system

All chemicals (purity > 98%) were purchased from Sigma-Aldrich (Steinheim, Germany) or Toronto Research Chemicals Inc. (North York, Canada) and were stored under recommended conditions until use. D-or 13 C-labeled chemicals were purchased from Toronto Research Chemicals Inc. and CDN Isotopes (Pointe-Claire Quebec, Canada). LC/MS-grade formic acid was purchased from Sigma-Aldrich. LC/MS-grade acetonitrile and methanol were purchased from VWR (Stockholm, Sweden). Milli-Q water was produced by using a Milli-Q Integral Water Purication System (Merck Millipore, Stockholm, Sweden). All standard stock solutions were prepared in methanol and stored in the dark at À20 C.

Chemicals used as standards for analysis were purchased from Sigma-Aldrich (Steinheim, Germany) or Toronto Research Chemicals Inc. (North York, Canada). D-and 13 C-labeled standards were purchased from Toronto Research Chemicals Inc. and CDN Isotopes (Pointe-Claire, Quebec, Canada). A solution containing all non-labeled standards and a solution containing all isotopelabeled standards were prepared at a concentration of 5 mg mL À1 in methanol and stored in the dark at À20 C until use. LC/ MS-grade acetonitrile and methanol were purchased from VWR (Stockholm, Sweden), and LC/MS-grade formic acid was obtained from Sigma-Aldrich. Sodium azide was purchased from Sigma-Aldrich. Milli-Q water was produced using a Milli-Q Integral Water Purication System (Merck Millipore, Stockholm, Sweden).

All non-isotope-labeled standards (purity >98%) were purchased from Sigma-Aldrich (Steinheim, Germany) or Toronto Research Chemicals Inc. (North York, Canada) and were stored under recommended conditions until use. The isotope-labeled standards were purchased from Toronto Research Chemicals Inc. and CDN Isotopes (Pointe-Claire Quebec, Canada). Details of these standards are provided in Tables S1 andS2 in the ESI. † Stock solutions of the standards were prepared in methanol and stored in amber CERTAN® capillary bottles in the dark at À20 C. LC/MS-grade formic acid and sulfuric acid were purchased from Sigma-Aldrich. LC/MS-grade acetonitrile, methanol, and sodium hydroxide were purchased from VWR (Stockholm, Sweden). Milli-Q water was produced by using a Milli-Q Integral Water Purication System (Merck Millipore, Stockholm, Sweden). A non-labeled standard mixture containing 42 standards of a broad spectrum of polar organic contaminants (Table S1 †) and an internal standard mixture containing 40 isotope-labeled standards (Table S2 †) were prepared in methanol at a concentration of 5 mg mL À1 ; both standard solution mixtures were stored in the dark at À20 C until use.