Investigation of phosphorus release from different compounds in electrothermal vaporization inductively coupled plasma atomic emission spectrometry in the absence and presence of modifiers and its application to plant analysis

Inductively coupled plasma atomic emission spectrometry (ICP-AES) combined with electrothermal vaporization (ETV) was applied to the determination of phosphates in aqueous solutions. The sensitivity for phosphorus was, found to depend on the cations in the sample. To understanding this phenomenon th e thermal behavior of H3PO4, (NH4)(2)HPO4 and KH2PO4 was studied. There wer e significant differences in the thermal release of phosphorus from these c ompounds. To explain these phenomena, different reaction mechanisms were ca lculated using thermodynamic data. La(NO3)(2) and Pd(NO3)(2) were successfu lly applied as modifiers for the stabilization of phosphates during the the rmal pre-treatment step and to establish an uniform thermal behavior. The a pplication of Pd(NO3)(2) as modifier led to uniformity in the thermal behav ior and to stabilization of different phosphates tested. This resulted in a good correspondence between the certified and the measured concentrations of total phosphorus in decomposed plant reference materials. The stabilizat ion of using La(NO3)(3) modifier bases on the formation of thermally stable LaPO4. This explanation has been supported by comparing the experimental r esults with thermodynamic calculations considering different reactions for the thermal decomposition of the phosphate. Unfortunately, there are no the rmodynamic data for palladium phosphates and phosphides available. (C) 2000 Elsevier Science B.V. All rights reserved.