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Direct chromatographic separation and quantification of calcium and magnesium in seawater and sediment porewaters


Melendez, M and Nesterenko, EP and Nesterenko, PN and Corredor, JE, Direct chromatographic separation and quantification of calcium and magnesium in seawater and sediment porewaters, Limnology and Oceanography: Methods, 11, (September) pp. 466-474. ISSN 1541-5856 (2013) [Refereed Article]

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Copyright Statement

Copyright 2013 by the American Society of Limnology and Oceanography, Inc.

DOI: doi:10.4319/lom.2013.11.466


Direct analysis of Ca2+ and Mg2+ is required for accurate determination of metastable carbonate mineral phase saturation states (ΩCaCO3; ΩMgCO3) in seawater, sediment porewaters, and other high ionic strength brines. To this end, we have implemented a method using High Performance Chelation Ion Chromatography (HPCIC) in which metal ion complexation at the stationary phase renders separation efficiency insensitive to high ionic strength matrix effects common to other ion chromatography (IC) methods. This method, using direct automated on-column injection, vastly increases sample throughput capacity in comparison to current titration methods. Calcium and magnesium ions in IAPSO standard seawater were selectively separated using a monolithic silica column (100 4.6 mm ID) activated with a covalently bonded iminodiacetic acid (IDA) chelator. The colored ion complexes resulting from post-column reaction (PCR) of the ions with a metallochromic indicator, in this case 4-(2-pyridylazo)-resorcinol (PAR), were detected spectrophotometricaly at 510 nm. Optimization of flow rate, eluent concentration, pH, and sample injection volume allowed baseline separation of Mg2+(0.05474 mol kg1) and Ca2+ (0.01065 mol kg1) in less than 8 min using 2 μL seawater sample injections. At a flow rate of 1 mL min1, peak elutions occurred respectively at 4 and 5 min, using an eluent containing 0.1 M potassium chloride and 1 mM nitric acid adjusted to pH 2.5. Retention time variability below 0.5% for both metals following more than 200 injections indicates long-term stability of the derivatized monolithic silica column. Method application to marine sediment porewaters is discussed.

Item Details

Item Type:Refereed Article
Keywords:calcium and magnesium, seawater, chelation ion chromatography
Research Division:Chemical Sciences
Research Group:Analytical chemistry
Research Field:Separation science
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the chemical sciences
UTAS Author:Melendez, M (Ms Melissa Melendez)
UTAS Author:Nesterenko, EP (Dr Ekaterina Nesterenko)
UTAS Author:Nesterenko, PN (Professor Pavel Nesterenko)
ID Code:88320
Year Published:2013
Web of Science® Times Cited:5
Deposited By:Chemistry
Deposited On:2014-01-28
Last Modified:2014-07-04

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