Chitin in the alpha form extracted from crab shells under hot alkaline conditions yielded chitosan with a degree of deacetylation of 80 + 1%. This was chemically modified with succinic anhydride, following either a homogeneous or a heterogeneous route. The anhydride reaction products in position 2 and 6: and 2, 3 and 6 of the chitosan were characterized by elemental analyses, carbon-13 NMR in the solid state, scanning electron microscopy. infrared spectroscopy and X-ray diffractometry. The second modified chitosan compound better adsorbs copper from aqueous solution and gave a cyclic voltammetric response when divalent copper nitrate was used as a mediator, with high stability in potassium chloride electrolyte solutions. The cyclic voltammetric studies with different scan rates and the potential of the electrode versus pH indicated that the electrode constructed with chitosan-succinate copper ion presents stability for approximately one month, suggesting its use as a biosensor. (c) 2006 Elsevier Ltd. All rights reserved.643385390