Determination of trace magnesium and strontium in calcium carbonate and calcareous skeletons of marine planktonic organisms using high performance chelation ion chromatography

摘要

A new high performance chelation ion chromatography method for the simultaneous determination of trace magnesium and strontium in various calcium carbonate samples was developed. Separations were performed on a monolithic silica column (Chromolith Si, 100 x 4.6 mm I. D.) chemically modified with hydroxyethyliminodiacetic acid functional groups. At a flow rate of 1.0 mL min(-1), an eluent containing 80 mM NaCl and 20 mM picolinic acid at pH 5.30 was found to provide complete separation of Ni2+, Cu2+, Mg2+, Cd2+, Sr2+ and Ca2+ in 15 minutes, in matrices with 20 000 fold excess of Ca2+. Two post-column reagents, o-cresolphthalein complexone (o-CPC) and ZnEDTA-PAR, were compared for post-column reaction based photometric detection at 570 and 490 nm, respectively. This method provides sensitive detection of Mg2+ (LOD 20 mu g L-1 and 5 mu g L-1 for o-CPC and ZnEDTA-PAR, respectively) and Sr2+ (LOD 200 mu g L-1 and 39 mu g L-1 for o-CPC and ZnEDTA-PAR, respectively). Using o-CPC, the linear range was from 0.5 to 24 mg L-1 for Mg2+ and from 1.0 to 32 mg L-1 for Sr2+. For ZnEDTA-PAR, the linear range was from 0.5 to 4 mg L-1 for Mg2+ and 0.1 to 32 mg L-1 for Sr2+. The method was applied to the analysis of a variety of calcium carbonate samples, including laboratory reagents, limestone NIST certified reference material, and the calcite based shells of marine microorganisms. The accuracy of the method was confirmed using inductively coupled plasma mass spectrometry.