Hollow fiber–liquid phase microextraction of barbiturates in liver samples

Barbiturates, especially phenobarbital, are involved in intoxication cases in Brazil and other countries. Liver tissue can be a useful alternate specimen when blood is not available (decomposition, severe fire, and exsanguination cases). Because the liver is a very complex matrix, it is essential is to eliminate potential interfering substances in this specimen before instrumental analysis of target compounds. In recent years, novel strategies for sample preparation have gained acceptance in the field of analytical toxicology. The objective of this work was to develop a gas chromatography–mass spectrometry (GC–MS) method using hollow fiber–liquid phase microextraction (HF–LPME) for determination of barbiturates (phenobarbital, secobarbital, pentobarbital, and butalbital) in liver samples. An aliquot of homogenized and acidified liver in aqueous solution (equivalent to 50 mg tissue) was submitted to extraction by the use of a 9-cm hollow fiber. The fiber was filled with eucalyptus oil in its pores and its lumen was filled with a NaOH solution (pH 13; acceptor phase). After extraction in an ultrasonic bath for 5 min, the acceptor phase was withdrawn and derivatized in the injector port of the GC–MS with trimethylanilinium hydroxide for flash methylation. A totally “green chemistry” approach of the sample extraction was obtained, because relatively large amounts of organic solvent generally used for extraction could be substituted by an essential oil used as a supported liquid membrane for HF–LPME. This method was validated and successfully applied to liver samples collected from five deceased persons with previous history of exposure to barbiturates. Phenobarbital concentrations in the liver found in these actual cases ranged from 1.3 to 16.7 μg/g.