Tube ageing as an important quality factor in the direct determination of Sb in solid samples by ultrasonic slurry sampling-GFAAS

Abstract

Although graphite deterioration occurs in all the GFAAS-based techniques, this issue is of most concern whenever solid samples are introduced in the graphite tube as slurries because of the different behaviour they show regarding solutions. In this work several factors were considered to evaluate their influence on the tube ageing, the nature and amount of sample matrix introduced into the atomiser (and so the concomitants) being the most important ones. Scanning electron microscopy and X-ray dispersive analyses were employed to assess the L’vov platform degradation, not only regarding its morphology but the chemical nature of the deposits observed on it. Three modes of sample handling were studied: aqueous solutions, acid extracts and slurries. Changes in the useful lifetime of the tube were studied when analysing Sb in different matrices (soils, sediments, coals, coal fly ashes and slag) and empirical solutions were presented to expand the lifetime of the tube. Coal revealed itself to be the most difficult matrix to deal with and several slurry methodologies were assayed: introduction of an oxidative step, external ashing, enlargement of the temperature program and two extracting media.