Phenol, Phenols, or Phenolics?

post96What is the difference between phenol, phenols and phenolics? These terms have often caused confusion in environmental analysis. A phenol (or hydroxybenzene) is a single organic compound. “Phenols” refers to the class of aromatic compounds having a hydroxyl (-OH) group, as well as other substituent groups, on a six-carbon benzene ring or prior to the introduction of the list of priority pollutants in the late 1970’s, to the colorimetric analyses of phenols. “Phenolics” is the title used for the USEPA SW-846 Methods 9065 and 9066 for the colorimetric measurement of numerous known and unknown substances with one or more hydroxyl groups attached to a benzene ring. The organic compound, phenol, is the chemical used to calibrate the colorimetric test for the classes of compounds known as phenols or phenolics.

EPA’s list of priority pollutants includes a number of phenols measured in the acid fraction of the base/neutral/acid (BNA) analysis (or the semivolatile organic compounds analysis) using EPA Methods 525, 625, 1625, and 8270. These phenols include:

2,4-dimethylphenol

phenol

p-cresol (4-methylphenol)

2,6-dichlorophenol

2,3,4,6-tetrachlorophenol

2-chlorophenol

2-nitrophenol

2,4-dichlorophenol

4-chloro-3-methylphenol

2,3,6-trichlorophenol

2,4-dinitrophenol

4-nitrophenol

2-methyl-4,6-dinitrophenol

pentachlorophenol

o-cresol (2-methylphenol)

2,4,5-trichlorophenol

2,4,6-trichlorophenol

Note that phenol is included in the list of the priority pollutants.

Each of the priority pollutant phenols, including phenol itself and the para-substituted phenols, can be found, identified, and quantified by several gas chromatographic/mass spectrometric EPA methods such as 525, 625, 1625, and 8270. The colorimetric analytical procedures entitled phenols or phenolics measure many compounds and provide a quantitative result for phenols or phenolics as a class. However, no specific compound can be identified or quantified using the colorimetric method. Consequently, if a sample is analyzed by one of the colorimetric methods, no specific phenolic compound, including phenol itself can be stated to be present in the sample and is reported by this laboratory as “total recoverable phenols”.

Phenols may occur in domestic and industrial wastewaters, natural waters and potable water supplies. Chlorination of these waters may produce odorous and objectionable-tasting chlorophenols. Decaying vegetation and, in particular, wood produces numerous phenols because the benzene with the hydroxyl group is in a major portion of a woody substance called lignin. Lignin is removed from paper pulp made from trees and degrades to form numerous substances including phenols. These phenols include humic and fulvic acids, large molecules of organic matter that are soluble in water, as well as aromatic substances with several hydroxyl groups on the benzene ring. These phenolic compounds can and do form groundwater plumes emanating from swamps and wetlands, and the plumes can contain a variety of phenols. Again, a positive result from colorimetric analysis can only tell you that the hydroxy benzene structure is present. It cannot tell you what specific compounds are present.