
TY  - JOUR
A1  - Mendz, GL 
T1  - Factors Influencing the Measurement of Calcium Concentrations in Biological Fluids by <sup>19</sup>F N.M.R. Spectroscopy
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1994
VL  - 47
IS  - 4
SP  - 677
EP  - 692
KW  - 
UR  - https://doi.org/10.1071/CH9940677 
N2  - Fluorinated derivatives of fluorescent calcium probes have been recently used to measure free calcium concentrations in biological fluids by 19F n.m.r. spectroscopy. To measure calcium levels a method utilizes the change in chemical shift experienced by the fluorine resonance of the calcium chelator 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N&#8242;,N&#8242;- tetraacetic acid upon complexation of cations. The procedure assumes that (A) the fluorinated probe is in equilibrium between the calcium complex and the free acid form; (B) the chemical exchange between different sites has similar effects on the intensities of the observable resonances; and (c) the presence of macromolecules affects equally the intensities of the resonances arising from different complexes. Experiments designed to test these assumptions were carried out in plasma and in model systems containing mixtures of cations and macromolecules. The results indicated that in biological fluids the calcium probe is involved in a multisite equilibrium in which 'invisible' (very broad) peaks affect the equilibrium intensities of the 'observable' peaks. Binding to macromolecules affected differently the intensities of the resonances arising from different complexes in the spectrum of the chelator , and influenced significantly the calculated free calcium concentrations. 
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