A method is presented in which gas chromatography coupled with mass spectrometry (GC-MS) allows quantitative simultaneous detection of mixtures of phenol (Ph), 2-chlorophenol (2-CPh), 3-cholorphenol (3-CPh), and 4-cholorophenol (4-CPh) in aqueous mixtures after being adsorbed on silicalita-1, utilizing selected-ion monitoring (SIM) and full-scan modes mass selective detection. GCMS with SIM at <em>m/z</em> = 64 and <em>m/z</em> = 128 showed good detection selectivity for mixtures of Ph, 2-CPh and 3-CPh (M₁), and 2-CPh and 4-CPh (M₂). Silicalita-1 was obtained from an amorphous organo-alumino-silicic gel from rice husk, an abundant and low cost agricultural waste residue that is readily available in large quantities. This product was used as a sorbent for solid phase extraction of organic analytes from aqueous solutions. The adsorption of the three chlorophenol isomers, <em>ortho</em>-, <em>meta</em>-, and <em>para</em>-, by silicalite-1 has been studied independently, showing that <em>meta</em>- and <em>para</em>-chlorophenol isomers are adsorbed more than <em>ortho</em>-chlorophenol. However the adsorption behavior of mixtures of these isomers was not reported. In this work, it was found that when the ortho-isomer is mixed either with <em>meta</em> or <em>para</em>-chlorophenol, considerable differences were observed in the adsorption process; in the studied mixture, the <em>ortho</em>-isomer was adsorbed more than the <em>meta</em>-and <em>para</em>-chlorophenol.