On-line solid phase extraction-capillary zone electrophoresis for the simultaneous determination of lanthanum and gadolinium at picogram per liter levels

VIZIOLI, NORA; GIL, RAÚL ANDRÉS; MARTÍNEZ, LUIS DANTE; SILVA, MARÍA FERNANDA

Sevilla, España

Simposio; 20. XIV Simposio Latinoamericano en Aplicaciones de la Electroforesis Capilar y Tecnología del Microchip en Biotecnología, Biomedicina , Biofarmacia e Industria; 2009

During the last three decades, the use of rare earth elements (REEs) in manufactured goods have resulted in a wide variety of electromechanical and metallurgical devices to glasses, superconductors, supermagnets, lasers and electronic components. REEs have been applied in fertilizers for the agriculture with the consistent bioaccumulation of REEs in plants, soils and water. Indeed, they are extensively applied in medical fields; gadolinium is widely employed as a contrast agent for magnetic resonance imaging while lanthanum is used as calcium- and aluminum-free phosphate binder for the treatment of hyperphosphatemia of chronic renal failure.  A non-specific on-line method is presented for the extraction and preconcentration of two rare earth elements (REEs) using a microcartridge containing C18 derivatized silica particles prior to their analysis by capillary zone electrophoresis. The microcartridge, named analyte concentrator, was coupled on-line to the inlet of the separation capillary (fused-silica capillary, 75 mm ID x 12 cm from the inlet to the microcartidge and 37 cm from the microcartridge to the detector). The reversed-phase sorbent quantitatively retained Gd and La as 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) complexes in the presence of non-ionic micelles of polyethylene glycol tert-octylphenyl ether (Triton X-100), enabling sample clean-up and concentration enhancement with minimum sample handling. The REEs chelates were released from the sorbent with methanol and then analyzed by CZE with diode array detection. A background electrolyte of 20 mM sodium tetraborate containing 8% ACN, pH 9.0, was found to be optimal for the separation of metal chelates. The concentration limits of detection (CLODs) were lowered to picogram per liter levels (20 pg/L for La and 80 pg/L for Gd). A 1000-fold improvement in concentration sensitivity for La- and Gd-5BrPADAP complexes with respect to CZE without preconcentration was reached.