The behaviour of the arsenic hydrides, generated after the speciation of AsIII (arsenite), MMAs (monomethylarsonate) and DMAs (dimethylarsinate), in an atomic fluorescence cell was investigated. The efficiency of the hydride generation process was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) after sampling the liquid drain of the gas-liquid separator and by a gas chromatograph with mass spectrometric detection (GC-MS) for the analysis of the sampling gas of the separator. The different concentrations at which the fluorescence signal reaches a maximum were determined for each As species.