On-line deproteinization by adsorption of proteins on a polyethylene powder pre-column for the determination of Na, K, Mg and Ca in human serum by high-performance liquid chromatography

Deproteinization of human serum was carried out on-line using a polyethylen e powder cartridge as pre-column. The serum sample, after dilution, was inj ected into the chromatograph, and when passing through the cartridge the pr oteins were adsorbed by the polyethylene. A protein-free eluate was carried to the analytical column while the pre-column was washed with methanol and water to elute the adsorbed proteins by changing the pump channels. After washing, the pre-column was conditioned with the eluent to receive the next sample. Deproteinization was evaluated off- and on-line using pooled serum , and testing the protein residue after passing through a polyethylene cart ridge with the Comassie Brilliant Blue reaction. Parameters such as serum v olume, eluent and washing solution were investigated. Sodium, potassium, ma gnesium and calcium determinations were performed by high-performance liqui d chromatography with conductimetric detection. The proposed method is suit able for the determination of these cations in serum samples without furthe r treatments. The total analysis time was about 20 min and a linear range f rom 0.3 to 1.2 mg/l for sodium, potassium, magnesium and calcium was observ ed. The method was characterized by a precision of about 95% and recoveries from spiked samples were between 96 and 102%. The results for serum sample s analysed by the proposed method were compared with photometry and atomic absorption spectrometry. (C) 2001 Elsevier Science B.V. All rights reserved .