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 the thermal behavior of H3PO4, (NH4)2HPO4 and KH2PO4 was studied. There were significant differences in the thermal release of phosphorus from these compounds. To explain these phenomena, different reaction mechanisms were calculated using thermodynamic data. La(NO3)3 and Pd(NO3)2 were successfully applied as modifiers for the stabilization of phosphates during the thermal pre-treatment step and to establish an uniform thermal behavior. The application of Pd(NO3)2 as modifier led to uniformity in the thermal behavior 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 stabilization of using La(NO3)3 modifier bases on the formation of thermally stable LaPO4. This explanation has been supported by comparing the experimental results with thermodynamic calculations considering different reactions for the thermal decomposition of the phosphate. Unfortunately, there are no thermodynamic data for palladium phosphates and phosphides available.