Anion-exchange (AE) high-performance liquid chromatography (HPLC) with ICP-MS detection was revisited for speciation of arsenic in biomaterials with particular attention given to arsenic-containing ribosides (arsenosugars) in seaweeds. Signal identification by retention time matching and spiking experiments was found to be difficult because of the co-elution of the ribosides with other arsenic species [As(III), monomethylarsonic acid], the medium- and long-term irreproducibility of retention times of arsenic species and an uncontrolled matrix effect on the retention times. Size-exclusion (SE) HPLC was proposed for the fractionation of organoarsenic species and matrix removal prior to detection of arsenosugars by AE-HPLC followed by signal identification by spiking experiments and retention time matching. The results were compared with those obtained by pneumatically-assisted electrospray tandem MS (ESI MS/MS) of the SE-HPLC fractions. A number of 10 commercially available edible algal food samples of different origins available on the French market were investigated. The approaches developed for the identification and determination of arsenosugars (SE-AE-HPLC-ICP-MS and SE-HPLC-ESI MS/MS) were discussed using the example of Hizikia fusiforme.