Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)A rapid and selective method to determine p-chloroaniline (pCA) in gel, 2 % aqueous solutions, and 0.12 % oral rinse formulas of chlorhexidine digluconate (CHX) used in dentistry treatments was developed and validated. The method was appropriate for ensuring that these products are in accordance with current legislation. Furthermore, the precipitate formed when 2 % CHX is added to sodium hypochlorite was investigated to verify whether this mixture forms pCA. To quantify pCA, liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was used and the following m/z 127.9/93.0 and 127.9/111.0 were used as qualifier and quantifier transitions, respectively. The LC separation, using a C-18 column proved highly efficient for pCA and its isomers, i.e., m-chloroaniline and o-chloroaniline. Multiple reaction monitoring provided the proper selectivity and specificity for the method. Commercial aqueous solutions, gels, and oral rinses containing CHX were analyzed, and their pCA contents complied with those recommended by the European and United States Pharmacopeias. The method was also able to detect pCA in the precipitate and its concentration is below 0.1 %.7913-14841849FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)