SOLID SAMPLING ELECTROTHERMAL VAPORIZATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY FOR THE DETERMINATION OF ARSENIC IN STANDARD REFERENCE MATERIALS OF PLANT-ORIGIN

The direct determination of As in solid samples of plant origin using electrothermal vaporization inductively coupled plasma mass spectromet ry (ETV-ICP-MS) is reported. The first phase of the work consisted of an optimization of the carrier gas bow rate and the heating cycle of t he modified graphite furnace lashing and vaporization temperatures). A systematic study of the signal profiles (signal intensity as a functi on of time) showed that As coming from the solid samples and As coming from Liquid standards added to the solid material, only showed an ana logous behaviour on condition that these liquid spikes were previously dried before the solid sample was introduced into the sample boat. Th e potential of the technique was assessed by establishing figures of m erit and analysing some standard reference materials for As, An absolu te limit of detection of approximately 1 pg was established for As, co rresponding to a relative limit of detection of approximately 1 ng g(- 1) for a typical sample mass of 1 mg. Results obtained for the As cont ent in the samples analysed were not deteriorated by the presence of C l, as even on addition of amounts of Cl exceeding the Cl content of th e samples no (ArCl+)-Ar-40-Cl-35 interference on the As-75(+) signal c ould be established. For the determination of As in these reference ma terials of plant origin, several methods of calibration were investiga ted, including external calibration using both liquid and solid standa rds and single standard addition. The use of an internal standard (Sb) was studied and its requirement was assessed as being from advisable to imperative, depending on the calibration method used. Although seve ral methods offered possibilities for accurate determination (mean dev iation between ETV-ICP-MS results and certified values < 10%), single standard addition was assessed to be the most practicable and straight forward method.