Error in the calibration of the mgatp chemical‐shift limit: Effects on the determination of free magnesium by 31P NMR spectroscopy

Abstract
The measurement of free intracellular magnesium (Mg2+) using the 31P chemical shifts of ATP requires the use of appropriate calibration solutions to determine the chemical-shift limits ΔATPαβ and ΔMgATPαβ. Solutions containing excess Mg2+ contain significant amounts of Mg2ATP and yield positive errors in the value of ΔMgATPαβ. For physiological applications this may overestimate free intracellular Mg2+ by as much as 300%. This error may be minimized if appropriate mole ratios of Mg2+/ATP are used to calibrate ΔMgATPαβ. © 1992 Academic Press, Inc.