Developing a robust LC-MS/MS method to quantify Zn-DTPA, a zinc chelate in human plasma and urine

Quantitation of Zn-DTPA (zinc diethylenetriamene pentaacetate, a metal chelate) in complex biological matrix is extremely challenging on account of its special physiochemical properties. This study aimed to develop a robust and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determination of Zn-DTPA in human plasma and urine. The purified samples were separated on Proteonavi (250 × 4.6 mm, 5 μm; Shiseido, Ginza, Tokyo, Japan) and a C₁₈ guard column. The mobile phase consisted of methanol-2 mm ammonium formate (pH 6.3)-ammonia solution (50:50:0.015, v/v/v), flow rate 0.45 mL/min. The linear concentration ranges of the calibration curves for Zn-DTPA were 1-100 μg/mL in plasma and 10-2000 μg/mL in urine. The intra- and inter-day precisions for quality control (QC) samples were from 1.8 to 14.6% for Zn-DTPA and the accuracies for QC samples were from -4.8 to 8.2%. This method was fully validated and successfully applied to the quantitation of Zn-DTPA in plasma and urine samples of a healthy male volunteer after intravenous infusion administration of Zn-DTPA. The result showed that the concentration of Zn-DTPA in urine was about 20 times that in plasma, and Zn-DTPA was completely (94.7%) excreted through urine in human.