Direct determination of transition metals in mussel tissue digests using high-performance chelation ion chromatography with monolithic silica based chelating ion exchangers

A new high performance chelation ion chromatography method was developed for the direct separation and detection of selected transition metals in shellfish (mussel) tissue digest samples. Using two different bonded silica monolithic chelating stationary phases, exhibiting differing selectivities for metals of interest, were applied within the method. The bonded chelating chemistries were N-hydroxyethyliminodiacetic (HEIDA) and N-(2-hydroxyethyl)-N-(2-[phosphonomethyl)amino]acetic (HEPMA) acids. Quantitative determination of Mn(II), Cd(II) and Zn(II) concentrations within shellfish tissue (Mytilus edulis), following microwave assisted acid digestion. Post-column detection was achieved using spectophotometric detection at 510 nm after reaction with 4-(2-pyridylazo) resorcinol. The eluents employed were 0.5 M KNO₃, pH 2.4, for the HEIDA-bonded stationary phase, and 0.1 M KNO3, pH 2.6, for the HEPMA-bonded monolithic column. The HEPMA phase provided improved resolution between Mn(II) and interfering alkaline earth metal cations compared to the HEIDA-bonded phase. Concentrations of metals were determined using standard addition, and Cd(II), Mn(II), and Zn(II) cations were detected at <10 μg g⁻¹, <50 μg g⁻¹ and <700 μg g⁻¹, respectively. Sample analysis using sector field inductively coupled plasma-mass spectrometry (ICP-MS) was carried out to generate comparative data to that obtained using the chromatographic method.