Extraction of residual heavy metals from commercial chitosan and approach to preparation of oligochitosan hydrochloride

Abstract

For biomedical applications, chitosan and oligochitosan must be appropriately characterized and meet pharmacological requirements in terms of contamination by residual heavy metals.In this work, a series of commercial chitosans was analyzed by ICP-MS method, and high concentration of Fe (44–382 ppm), Cr (3.1–35.5 ppm) and Ni (0.33–7.91 ppm) exceeding pharmacologically acceptable level was found. It was shown that as a chelating agent EDTA was an ineffective remedy for solid-phase extraction of residual heavy metals from chitosan. It was proposed that corrosion of stainless steel apparatus in the process of chitin deacetylation contributed to chitosan contamination by heavy metals. A two-step treatment of chitosan with hydrochloric acid allowed remediation of chitosan and preparation of oligochitosan hydrochloride with molecular weight 5–16 kDa and acceptable level of Fe<10, Cr<1 and Ni<1 ppm.