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  • Title: Analytical variables affecting exchangeable copper determination in blood plasma.
    Author: Buckley WT, Vanderpool RA.
    Journal: Biometals; 2008 Dec; 21(6):601-12. PubMed ID: 18546054.
    Abstract:
    To resolve discrepancies observed in the determination of plasma exchangeable Cu (also called direct reacting Cu or loosely bound Cu) by several methods, plasma storage techniques and various aspects of a stable isotope dilution procedure for exchangeable Cu were evaluated. Results indicated that the exchangeable Cu fraction of plasma increased with storage at room temperature, at 5 degrees C and when subjected to repeated freeze/thaw cycles. Samples could be safely stored at -65 degrees C. Exchange between added 65Cu2+ and endogenous plasma Cu rapidly went to completion in the isotope dilution procedure. Analytical results were unaffected by shaking method, sample size or the presence of heparin. A small difference was observed between serum and plasma. The determination of exchangeable Cu did not vary over a period of 4 h when plasma was exposed to 1.6 x 10(-4)-M sodium diethyldithiocarbamate (used in the isotope dilution method) but steadily increased when exposed to 1.1 x 10(-2)-M sodium diethyldithiocarbamate, which suggested that tightly bound Cu (probably in ceruloplasmin) was exchanging with isotopic tracer at the higher concentration. Determination of exchangeable Cu was constant from pH 7.2-8.5 but increased substantially at higher pH. Complete recovery of natural Cu added to plasma was obtained. Studies in solution indicated that 65Cu2+ exchanged readily with albumin- and amino acid-bound Cu. Ultrafiltration of plasma yielded a Cu fraction about half that of the exchangeable Cu fraction. We conclude that the stable isotope dilution procedure for plasma exchangeable Cu yields reliable, physiologically meaningful results.
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