Abstract Extraction of sediments with phosphoric acid (0.5 M) and hydroxylamine hydrochloride (0.1 M) allowed the measurement of labile arsenic species while preserving the two redox states of arsenic. The forms and concentrations of arsenic species were measured using HPLC–ICP-MS. A Hamilton PRP X-100 strong anion exchange column using a 20 mM ammonium phosphate buffer (pH 6 and 9.2) was used to separate arsenic species. Recoveries of sediments spiked with As(V) were quantitative whereas for sediments spiked with As(III) recoveries of between 89 and 104% were obtained from four oxic certified reference sediments and an anoxic sediment. Application of the method to sediment samples from the marine Lake Macquarie, NSW, Australia, indicate that anoxic sediments can contain high concentrations of As(III), and two arsenosugars (sulfonate-ribose and sulfate-ribose). Extraction efficiencies for arsenic ranged between 6 and 82%. The arsenic species measured in sediments are strongly depended on the extraction procedure used. As(III) and arsenosugar concentrations in sediments that were freeze dried and oxidised were much less than in sediments that were not freeze dried and when exposure to air was keep to a minimum. Corresponding, As(V) concentrations tended to be higher in samples that were exposed to air.