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Total Phenols by Colorimetry (4-AAP)

Phenols by 4-Aminoantipyrine (4AAP) is a very common colorimetric method of analysis that provides a

quantitative result representative of total recoverable phenols. Although the 4-AAP and potassium ferricyanide

reagents react well with select phenol species (most effective in detecting non-substituted phenolic

compounds), this method has several shortcomings:

• Ortho- and meta- substituted phenolic compounds exhibit a lower response
• Phenolics substituted with an alkyl group in the para position (i.e. p-cresol) are not reportable using this method
• Phenols with an aryl, nitro, benzoyl, nitroso or aldehyde group are not reportable using this method
• Recoveries for phenols substituted with a single halogen can differ significantly (33% to 80%)1,2
• Recoveries decrease significantly as halide substitution increases
• Because this is a colorimetric method, it is also prone to interferences, either from other chemical species, chemical conditions (i.e. buffered pH) or physical conditions (colored extract)
• Because this method is considered a “total” analysis, phenol degradation products may contribute to the final result
• It should be noted that due to the significant shortcomings of the 4AAP colorimetric method, the 2016 CCME guidance documents on Analytical Methods for Contaminated Sites has removed this analysis from the list of acceptable methods

Phenolic Compounds by GC/MS (ABNs)

Unlike the method outlined above, the use of a gas chromatograph (GC) and mass selective detector (MS) in
Selected Ion Monitoring (SIM) mode allows for quantitative analysis of individual phenol compounds. For this analysis, the phenol species (summarized below) are extracted using an organic solvent, concentrated and analyzed using GC/MS. Because these parameters are a subset of a much larger scan of compounds, extracted under acidic, basic or neutral conditions, the list is also known as ABN Phenols. 

This analysis:

• Provides a more specific, sensitive and ultimately more reliable method for determination of individual
  parameters

• Allows for differentiating substituted from unsubstituted phenol species

• Provides much more information for the purposes of Environmental Forensics, by allowing for quantification
  of individual phenol species and subsequent source identification

• Like any other method, it can be affected by sample matrix interferences, but these can be easily assessed by leveraging laboratory QC data to determine potential impact

Can Total phenolics be reported from the GCMS method?

The GC/MS method is more sensitive, more specific and ultimately more reliable in quantifying phenolic compounds. Furthermore, the GC/MS method specifically lists quantitative results for individual phenolic compounds, rather than a total value. This allows for differentiating between substituted and non-substituted chemical species, as well as more accurately identifying the potential source of impact.