Determination of protein-free and protein-bound calcium and magnesium in biological samples by use of ultrafiltration and ion chromatography |
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| Affiliation: | 1. Department of Chemistry, Federal University of São Carlos, Rod. Washington Luís km 235, 676, São Carlos, 13560-970 SP, Brazil;2. Electrochemistry and Nanotechnology Laboratory, Research and Technology Institute/Processes Engineering Post-Graduation — PEP, Universidade Tiradentes, Av. Murilo Dantas, 300, Aracaju, 49032-490 SE, Brazil;1. Laboratory for Research of the Musculoskeletal System “Th. Garofalidis”, Medical School, National and Kapodistrian University of Athens, KAT General Hospital of Athens, Athens, Greece;2. Clinical Biochemistry Department, KAT General Hospital of Athens, Athens, Greece;3. 5th Orthopaedic Department, HYGEIA Hospital, Athens, Greece |
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| Abstract: | Protein-free and protein-bound calcium and magnesium are determined selectively in biological samples by use of ultrafiltration followed by ion chromatography. A commercial ultrafiltration kit is used to remove proteins of molecular weight > 10 000. The content of protein-bound cation is calculated by subtracting the value of protein-free from that of total cation. A protein-free cation filtrate is prepared by ultrafiltration of a diluted sample; a total cation filtrate is prepared by adding EDTA to the sample and filtering. Calcium and magnesium are determined in each filtrate by single-column ion chromatography with 1 mM EDTA (pH 6.5) as eluent and a conductivity detector. The use of a u.v. detector, in series with the conductivity detector, is useful for monitoring small molecules in the filtrates. The proposed method has been successfully applied to the determination of calcium and magnesium in blood serum, milk and egg white. |
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