“…For the pretreatment of plasma samples, some authors have used deproteinizing agents such as perchloroacetic acid followed by centrifugation and injection of the supernatant Stagni et al, 2004;Bangaru et al, 2000;Boulieu et al, 1997;Pham-Huy et al, 1999;Peh and Yuen, 1997;Jankowski et al, 1998). Some published studies describe the use of solid-phase extraction, resulting in extracts that are free of impurities and with high rates of drug recovery (Fernández et al, 2003;Poirier et al, 1999;Svensson et al, 1997;Kishino et al, 2002;Trottet et al, 2005).…”