Solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of arsenic in standard reference materials of plant origin

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Abstract
The direct determination of As in solid samples of plant origin using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) is reported. The first phase of the work consisted of an optimization of the carrier gas flow rate and the heating cycle of the modified graphite furnace (ashing and vaporization temperatures). A systematic study of the signal profiles (signal intensity as a function of time) showed that As coming from the solid samples and As coming from liquid standards added to the solid material, only showed an analogous behaviour on condition that these liquid spikes were previously dried before the solid sample was introduced into the sample boat. The potential of the technique was assessed by establishing figures of merit and analysing some standard reference materials for As. An absolute limit of detection of approximately 1 pg was established for As, corresponding 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 content in the samples analysed were not deteriorated by the presence of Cl, as even on addition of amounts of Cl exceeding the Cl content of the samples no 40Ar35Cl+ interference on the 75As+ signal could be established. For the determination of As in these reference materials of plant origin, several methods of calibration were investigated, including external calibration using both liquid and solid standards 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 several methods offered possibilities for accurate determination (mean deviation between ETV-ICP-MS results and certified values <10%), single standard addition was assessed to be the most practicable and straightforward method.

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