A method has been developed for the determination of seven arsenic species in mussel tissues by liquid chromatography—hydride generation—UV photo-oxidation and detection by inductively coupled plasma mass spectrometry. In order to determine the different species, two ion-exchange columns (anionic and cationic) were used with phosphate and nitric acid/ammonium nitrate as mobile phases, respectively. The optimisation of the conditions for separation, photo-oxidation and hydride generation is described. For each of these species, the limits of detection and repeatability are reported with the entire system coupling. This system was applied to the analysis of certified reference material (CRM 278) and mussels collected from Barcelona harbour. Extractions were achieved in methanol/water (1:1) using low-power focused microwaves as leaching process. As expected, arsenobetaine was the main compound extracted from both materials; the typical concentrations found were between 1 and 7 mg kg⁻¹. Other organoarsenical compounds, probably arsenosugars, were extracted in a concentration range of 0.3–1.5 mg kg⁻¹ in both cases. Amounts of dimethylarsinate (DMA) were found to be significant in the CRM 278, but very low in mussels from Barcelona harbour. The low limits of detection of the coupled system allow us to quantify low contents of other species (As(V), arsenocholine and monomethylarsonate (MMA)).