Nuclear-magnetic-resonance determinations of fluorine content and relaxation times in bone powder

Abstract

The detection of trace amounts of fluoride ions from ground rat-bone samples using a 27-MHz solid-state single-coil pulsed nuclear-magnetic-resonance (NMR) spectrometer is described. The fluorine content in the bone samples as determined from the amplitudes of the free-induction-decay (FID) signals is in good agreement with analyses based on standard chemical and neutron-activation techniques. The value of the spin-lattice relaxation time T₁ is 1.46 ± 0.07 s in dry rat-bone powder and is slightly longer in wet bone powder depending on the water content. The contribution of cross-relaxation processes to these results is discussed. The value of the spin–spin relaxation time T₂ (as determined from the point where the ¹⁹F FID signal has decayed to 1/e of its maximum amplitude) is approximately 75 μs. The Hahn echo sequence [(π/2)₀-τ-(π)₀] applied to 7 g of bone powder with a fluorine concentration of 3 mg F/g bone in a relatively homogeneous region of the external magnetic field yields echoes that persist for times 2τ up to ~0.5 ms.