Time-resolved Luminescence as a Novel Detection Mode for the Simultaneous High-performance Liquid Chromatographic Determination of Gadolinium–DOTA and Gd3+

Abstract

The simultaneous determination in aqueous media of the gadolinium ion (Gd³⁺) and the macrocyclic chelate Gd–DOTA (DOTA = 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid) used in magnetic resonance imaging (MRI) is described. The proposed approach combines a reversed-phase high-performance liquid chromatographic (RP-HPLC) separation and time-resolved luminescence detection (TRL). The spectroscopic properties of Gd–DOTA and various other Gd chelates (Gd–CDTA, Gd–TETA, Gd–EDTA, Gd–DTPA and Gd–TTHA) (CDTA = cyclohexanediaminetetraacetic acid; TETA = 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetra- acetic acid; EDTA = ethylenediaminetetraacetic acid; DTPA = diethylenetriaminepentaacetic acid; TTHA = triethylenetetraaminehexaacetic acid) were established in order to optimize TRL detection (λ_exc = 274 nm, λ_em = 313 nm, delay time 0.1 ms, gate time 10 ms). The Gd³⁺ ion possibly present in the matrix was detected as a Gd–CDTA chelate after dilution of the sample by a pH 7.6-buffered 1 × 10^–2M aqueous CDTA solution. Then, Gd–DOTA and Gd³⁺ ion (as Gd–CDTA chelate) were chromatographed on an RP C₈ HPLC column. The eluent consisted of pH 7.6 TRIS–HCl buffer + acetonitrile (98 + 2 v/v). The analytical figures of merit obtained for Gd–DOTA in aqueous solution were as follows: linearity was assumed from 10 to 5000 µmol l^–1; the limit of detection (LOD, S/N = 3) was 21 µmol l^–1, which corresponds to 235 ng of Gd–DOTA injected. The repeatability (RSD = 10%, n = 15) and the intra-assay reproducibility (RSD = 12%, n = 6) were studied for a 50 µmol l^–1 solution. With this method, 130 ng of Gd³⁺ ion (as Gd–CDTA) injected can be detected, which corresponds to an LOD of 42 µmol l^–1. The LOQ for Gd³⁺ ion was 140 µmol l^–1. Consequently, Gd³⁺ ion can be distinguished from chelated Gd–DOTA in aqueous solution (at the 0.2% level).