Abstract The extraction of arsenic species from mussel tissues is performed by using low power focused microwaves. The arsenic compounds are separated with anion-exchange liquid chromatography and detected by inductively coupled plasma mass spectrometry (ICP-MS). The extraction is optimised by applying a sequential Doehlert design, which allows us to quantify the influence of the microwave power, the exposure time and the relative proportions of methanol/water in the extraction medium. Well correlated second-order models are fitted to determine the extraction yields of arsenobetaine (AsBet), a probable arsenosugar (AsS), monomethylarsonate (MMA), dimethylarsinate (DMA) and As (V). By using focused microwaves the time of sample preparation is much shorter than in other methods. At powers close to 40 W with exposure times less than 4 min in methanol/water (55/45), the whole extraction yield reaches 85%. The proportion of species with respect to the total arsenic is 68% of AsBet, 14% of AsS+MMA and 2% of DMA.