Table 2.

Check list with recommended evidence, ranging from highly recommended (*****) to recommended (*), to establish both identity and degree of purity of synthetic PCB congeners in peer reviewed publications. See text for additional discussion.

Source of PCB derivatives: commercial source
• Source, purity and, potentially, catalog and batch numbers	*****
• Purification method(s) (e.g., column chromatography on alumina, silica gel or Florisil; charcoal treatment; and recrystallization), if any	*****
Source of PCB Derivatives: “in-house” synthesis
• Synthesis route, including starting materials and reagents, with appropriate citation(s) or, if no published previously, a detailed description of the synthetic procedure	*****
• Purification method(s) (e.g., column chromatography on alumina, silica gel or Florisil; charcoal treatment; and recrystallization)	*****
Identity of PCB congeners (as supplemental data)
• Description of the physical state (i.e., colorless solid, waxy solid or oil for PCB derivatives)	*****
• GC-MS chromatogram with using, for example, a typical 5% phenyl/95% dimethylpolysiloxane-based stationary phase and the corresponding mass spectruma	*****
• Proton and carbon NMR spectra (0–10 ppm for proton and 0–200 ppm for carbon NMR spectra, with expansions of multiplets)	****
• Accurate mass determination (within 0.0003 amu of the theoretical value calculated for the expected molecular formula)	***
• X-ray crystal structure determination	**
• Ultraviolet–visible (UV/Vis) spectrum	*
Degree of purity
• GC-MS chromatogram with using, for example, a typical 5% phenyl/95% dimethylpolysiloxane-based stationary phase and the corresponding mass spectrum (see above) as well as integration data, typically expressed as relative peak areaa	*****
• Proton and carbon NMR spectra (0–10 ppm for proton and 0–200 ppm for carbon NMR spectra; calibrated against TMS or CDCl3)	****
• Elemental analysis for carbon and hydrogen (and sulfur or nitrogen, if present) (within 0.4% of calculated values)	***
• Melting point range for all solid compounds (narrow melting point range that is in close agreement with a cited literature value)	***
• Purity determination by HPLC or LC-MS-based methods in certain cases (e.g., for PCB sulfates) to assess purity	**
• Congener-specific impurity analysis using GC-ECD, GC-MSb or biological assays (CALUX) to assess potent impurities targeting specific receptors for studies requiring highly pure compounds, including animal studies	*

^aSee Materials and Methods for a general procedure for the GC-MS analysis.

^bFor experimental details regarding the congener specific PCB impurity determination, see (Holland et al. 2016, Hu et al. 2015).