Method CP 86.07 is used to determine and confirm the concentrations of selected chlorinated phenols, chlorinated guaiacols, chlorinated catechols, chlorinated benzaldehydes (i.e., vanillins and syringaldehydes), and trichlorosyringol in extracts prepared from water samples by gas chromatography/mass spectrometry (GC/MS). This method is an updated version of NCASI Method CP 86.02 (NCASI 1986, 1997) which has been revised to meet the needs of the pulp and paper industry for the monitoring of chlorinated phenolics for the Cluster Rule (Federal Register 1998). Modifications to the method include: (a) a reduced analyte list (nonchlorinated compounds removed); (b) the addition of acenaphthene–d10 as an internal standard for quantitation of 3,4,5 trichlorophenol (in situ derivatization internal standard), 3,4,5 trichlorocatechol 13C6 (surrogate), and 5 bromovanillin (surrogate); (c) the use of potassium carbonate to adjust sample pH; (d) the addition of 5 bromovanillin as a surrogate for the chlorovanillins; and (e) the addition of 3,4,5 trichlorocatechol 13C6 as a surrogate for the chlorocatechols. Section 17, Table 1 lists the compounds which can be confirmed or determined by this method.