Water Quality Testing: What Parameters Are Actually Covered?

In water quality monitoring, “non-volatile phenol” is not the name of a single substance but a broad category of phenolic compounds defined by one operational criterion: whether they can be distilled out with water vapor. Phenols with boiling points below 230 °C are classified as volatile phenols, while those above 230 °C are classified as non-volatile phenols.

This boiling-point threshold correlates closely with molecular structure. Monohydric phenols—phenol itself, cresols, and xylenols—are volatile phenols. Dihydric and polyhydric phenols belong to the non-volatile group.

In practice, the parameters covered under “non-volatile phenol” in water testing therefore include the three benzenediols—catechol (o-dihydroxybenzene), resorcinol (m-dihydroxybenzene), and hydroquinone (p-dihydroxybenzene)—along with polyhydric phenols such as pyrogallol (1,2,3-trihydroxybenzene) and phloroglucinol (1,3,5-trihydroxybenzene), together with their substituted derivatives.

A key point for monitoring practice is that non-volatile phenols are not covered by the standard analytical methods developed for volatile phenols. The widely used 4-aminoantipyrine spectrophotometric method (HJ 503-2009) and the bromination volumetric method (HJ 502-2009) both target compounds that can be distilled with water vapor. Non-volatile phenols, with their high boiling points and low vapor pressures, remain in the distillation residue and are effectively excluded from these measurements.

This creates a regulatory blind spot. Current water quality standards, including the Surface Water Environmental Quality Standard and the Drinking Water Sanitary Standard, set limits for volatile phenols but do not list non-volatile phenols as independent control items. The rationale is partly practical: volatile phenols are more acutely toxic, more environmentally mobile, and have mature, standardized detection methods. 

Non-volatile phenols, however, are not harmless. They share the general protoplasmic toxicity of phenolic compounds, and in industrial effluents from coal washing, coking, synthetic ammonia, papermaking, and wood preservation, they often coexist with volatile phenols as part of a composite phenolic pollution load.

For targeted assessment, non-volatile phenols require techniques such as high-performance liquid chromatography, gas chromatography-mass spectrometry, or liquid chromatography-mass spectrometry, often with solid-phase extraction for enrichment.