Interference mechanisms and reduction during the speciation of organotin compounds by hydride generation, cryoseparation and detection by atomic absorption spectrometry
Résumé
Interferences generated by inorganic elements during the speciation of organotins and the effect of masking agents have been studied using hydride generation (HG) on-line with cryogenic trapping (CT), gas chromatographic (GC) separation and detection by atomic absorption spectrometry (AAS). This study was performed on a mixture of organotin species (monomethyltin (MMT), monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) at concentration levels of 5 ng of Sn of each in 50 ml of solution (100 ng I-1). Interfering elements (Al, As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Sb, Se or Zn) (100 μg), investigated individually in solution in the presence of the organotins, do not lead to the same signal depression for each organotin compound studied, possibly owing to different interference mechanisms. Interferences generated by inorganic elements can be partitioned between the solution and gaseous phases, showing that interferences may occur both during the solution and the gaseous steps for all organotins studied. Masking agents (EDTA and L-cysteine) to reduce interferences have been successfully used for organotin speciation. The presence of ethylenediaminetetraacetic acid (EDTA) in the reaction flask suppresses most of the interferences by forming complexes with the inorganic species and preventing them from reacting and altering the formation of DBT and TBT hydrides. However, EDTA also forms complexes with MMT and MBT. L-Cysteine improves the reproducibility and sensitivity of MBT determination and prevents the interfering effects of inorganic elements on the speciation of organotins. Interferences mechanisms are discussed.