Cadmium-bound species in human urine using high-performance liquid chromatography-vesicular hydride generation-inductively coupled plasma mass spectrometry

Abstract

Anion-exchange liquid chromatography was coupled on-line with inductively coupled plasma mass spectrometry (ICP-MS) via a vesicular hydride generation (HG) interface. This hybrid arrangement was assessed for Cd speciation in standards of rabbit liver metallothionein (MT) and human urine. Commercial rabbit liver MTs were readily resolved using a concentration gradient (2-200 mM) of Tris-HCl buffer solution at pH 7.4 and a polymeric Protein-Pak DEAE-5PW anion-exchange column. Three Cd species were detected in rabbit liver MT 1 [retention times of 3.2 (I), 5.6 (II) and 9.3 (III) min] and two species in MT 2 (retention times of 16.7 and 24 min). In rabbit liver MT 1 and MT 2, mixtures of Cd and Zn were found to be evenly distributed between the two isoforms, whereas Cu was predominantly associated with the MT 1 isoform.The chromatographic behaviour of the Cd-containing species separated and detected in basal human urine seems to be similar to that of the Cd fractions I and II of rabbit liver MT 1. The efficiency of CdH ₂ generation for Cd bound to both the main isoforms of rabbit liver was the same as for inorganic Cd ²⁺ from a vesicular medium. This highly selective and sensitive on-line HG-ICP-MS detection system provided a 4-fold (aqueous) or 16-fold (urine) sensitivity enhancement in comparison with ICP-MS detection with conventional nebulization. Unfortunately, only a 2-5-fold improvement was observed for the corresponding detection limits due to the high values of the blanks observed using volatile species generation.