The analysis of organic acids in smoke is performed using double derivatization. The acidic fonction is esterified in pentafluorobenzyl using pentafluorobenzyl bromide (PFB-Br). Since this method does not allow analysis for acids-alcools (e.g. lactic acid, glycolic acid) the alcohol function of these compounds was derivatized using pentafluropropionic anhydridous (PFPA). Both derivatizations were successively performed on the same extract without step operations. Afterwards the derivates were purified by solid phase extraction (SPE) upon a greffed cyanopropyl-dimethylsilyl phase. The acid extraction condensate was optimized so that the extract would contain light (acetic acid) and fatty acids (palmitic acid, stearic acid etc..). The analysis was achieved by gas chromatography on an apolar capillary column. Acids were detected using either an electron catching detector (ECD) or mass spectrometry in NICI mode (chemical ionization in negative mode). This method is extremely sensitive and specific and was used for mainstream and sidestream smoke studies as well as for the acid analysis in environmental tobacco smoke (ETS).