In this research, a headspace solid-phase microextraction (HS-SPME) method, based on sol–gel poly(ethylene glycol) reinforced with multi-walled carbon nanotubes (PEG/CNTs) coated fiber, prior to gas chromatography-flame ionization detector (GC-FID), was proposed for the determination of phenolic compounds in water and urine samples. Under the optimized conditions, the linear range for phenol and cresols was 0.005–100 ng mL
1, the limit of detection (S/N ¼ 3) was 0.001 to 0.1 ng mL
1 and the limit of quantification (LOQ) was 0.005 to 0.5 ng mL
1. The relative standard deviations (RSDs) for one fiber (repeatability) (n ¼ 5) were obtained from 5.4 up to 7.1%, and between fibers, or batch to batch (n ¼ 3), (reproducibility) in the range of 8.3–10.5%. The proposed HS-SPME-GC-FID method was successfully applied for the extraction of phenol and cresols from complex matrices such as wastewater and urine samples. Relative recoveries ranged from 85.3 to 99.5% for water samples and from 95.2 to 101.1% for urine samples. Introduction Phenolic compounds are among the most important contaminants, produced due to various processes such as plastic, explosive, dye, fertilizer, rubber, textile, drug and pesticide production.1–4 Phenols can cause protein degeneration, damage to the kidneys, liver and pancreatic tissue erosion, and also paralysis of the central nervous system in humans. Cresol and phenol, through precipitation of cellular proteins, can cause poisoning.5 Because of the toxicity, bioaccumulation, persistency in the environment and carcinogenic properties of these compounds, both the European Union (EU) and US Environmental Protection Agency (EPA) classify phenol, chlorophenols and cresols as priority pollutants. The European Community (EC) determined a legal tolerance level of 0.1 mg L
1 for each phenolic compound and 0.5 mg L
1 for the sum of all compounds in water used by humans.6,7 Because the maximum contaminant level (MCL) for many contaminants is very low (sub ng mL
1), very sensitive analytical methods are in high demand. Various methods, such as spectrophotometry,8 electrochemical methods,9 gas chromatography (GC)10 and liquid chromatography (LC)11 have been described in the literature for the determination of phenolic compounds in water samples. Solid-phase microextraction (

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