Direct determination of Cu isotope ratios in dried urine spots by means of fs-LA-MC-ICPMS. Potential to diagnose Wilson's disease

Abstract

This work investigates the potential of a 257 nm femtosecond (fs) laser ablation (LA) device operating at a high repetition rate (10 000 Hz) coupled to a multicollector (MC)-ICPMS to develop a method for the direct determination of Cu ratios in dried urine spots, prepared by deposition of urine (300 μL) onto precut clinical filter paper discs (16 mm diameter). The sampling capabilities offered by the fs LA system, permitting ablation of 150 μm thick coronas in the rim area of the filter, together with the use of admixed Ni as an internal standard, the proper optimization of the MC-ICPMS conditions (e.g., use of pseudo high-resolution mode to avoid interferences) and the use of a data processing approach particularly suitable for short transient signals (linear regression fit) enabled analysis of real urine samples with precision values around 500 ppm (RSD) for urinary Cu contents of a few hundred μg L−1. The methodology developed could prove to be useful for implementing screening protocols to detect Wilson's disease (WD), a well-known disorder related to Cu metabolism. In fact, the use of this analytical methodology permitted us to observe significant differences between (i) untreated WD patients and (ii) WD patients that are under treatment and control samples. This work represents the first time that determination of 65Cu/63Cu ratios has been used in the context of WD research, and serves as a proof of principle, suggesting that Cu isotope analysis could help in developing earlier and more reliable means to diagnose WD.