Determination of free gadolinium(3+) as a cyclohexanediaminetetraacetic acid complex by reversed-phase HPLC in ionic gadolinium(III) chelates

A reversed-phase HPLC method to analyze free Gd[sup 3+] in ionic Gd chelates, Gd(EDTA)[sup [minus]], Gd(DPTA)[sup 2[minus]], and Gd(DOTA)[sup [minus]], was developed. In the method, free Gd[sup 3+] was complexed with cyclohexanediaminetetraacetic acid (CDTA). Either the complexation was carried out before analysis or CDTA was added to the buffered mobile phase (pH 7.4, Tris-HCI) to complex the free metal in the chelate sample. The complex Gd(CDTA)[sup [minus]] was separated from the ionic chelate by high-performance liquid chromatography on a C[sub 18] reversed-phase Nucleosil column. A fluorescence detection method with 280-and 310-nm excitation and emission wavelengths, respectively, was used for monitoring. The recoverability, the linearity, and the limit of detection (LOD) of the method were determined. The method was evaluated in terms of thermodynamic and kinetic properties of Gd(CDTA)[sup [minus]], Gd(EDTA)[sup [minus]], Gd(DTPA)[sup 2[minus]], and Gd(DOTA)[sup [minus]]. The LOD for Gd[sup 3+] in the ionic chelates was 39 ng. 27 refs., 4 figs., 3 tabs.