Speciation analysis of nickel in the latex of a hyperaccumulating tree Sebertia acuminata by HPLC and CZE with ICP MS and electrospray MS-MS detection

Abstract

Speciation of nickel was investigated in a hyperaccumulator tree, Sebertia acuminata, by liquid chromatography (LC) with parallel ICP MS and electrospray MS-MS detection. The latex of the tree was leached with water. Two separation mechanisms, size-exclusion (SEC) and capillary zone electrophoresis (CZE), were investigated for the separation of Ni-complexes. A preparative scale SEC allowed the isolation of six stable nickel species. A nickel complex with M_r 360 was identified by ES MS. The collision induced fragmentation (CID) of the m/z 360 ion suggested the presence of three carboxylic and one amino groups, and allowed the identification of a Ni-complex with nicotianamine. A modification of the SEC column with Ni²⁺ ions allowed the isolation of a fraction containing nickel citrate. Quantification of the species showed that in the water extract of the latex 99.4% of the nickel is complexed by citrate and 0.3% by nicotianamine.