Solid-state 13 C and 31 P NMR analysis of urinary stones

We investigated the applicability of solid-state nuclear magnetic resonance (NMR) spectroscopy to obtain information about the structure and composition of renal calculi.

Various types urinary and bladder stones as well as a variety of presumed constituents were investigated using 13C and 31P magic-angle spinning (MAS) solid-state NMR. Different experimental methods were applied to differentiate resonances from crystalline/amorphous (immobile/mobile) as well as protonated/non-protonated moieties. The NMR spectra were analyzed using multiple-component numerical simulations and iterative fitting to identify and quantify the major amorphous or crystalline organic and inorganic components.

By comparison of the NMR spectra for the various renal calculi with those obtained under similar conditions for various presumed components, it is demonstrated possible to unambiguously distinguish and quantify the major amorphous or crystalline organic and inorganic components. The components are identified in terms of their isotropic and anisotropic chemical shielding parameters, protonation or proximity of protons, and the degree of crystallinity/mobility. For the calculi investigated we have detected and quantified calcium oxalate, uric acid, struvite, and calcium phosphates that closely resemble brushite and calcium hydroxyapatite.

Using 13C and 31P MAS NMR spectroscopy we have been able to account for 60 to 85% (by weight) of the constituents in the calculi investigated. The ability to identify and quantify both crystalline and amorphous components makes solid-state NMR an interesting new method for the compositional analysis of renal calculi.