INVESTIGATION OF SULFUR RELEASE IN ETV-ICP-AES AND ITS APPLICATION FOR THE DETERMINATION OF SULFATES

Electrothermal vaporization inductively coupled plasma atomic emission spectrometry was applied to the determination of sulfur species in aq ueous solutions. The sensitivity for sulfur as sulfate was found to be depending on the cations in the sample. For understanding this phenom enon the thermal behavior of sulfuric acid, ammonium sulfate and the s ulfates of sodium, zinc, magnesium and silver was studied. There were significant differences in the thermal release of sulfur from these su lfates. To explain these phenomena different reaction mechanisms were calculated using thermodynamic data. Pd(NO3)(2) and Ge in KOH were suc cessfully applied as modifiers for the stabilization of the sulfates d uring the thermal pre-treatment step and to establish a uniform therma l behavior of different sulfates. The stabilization of sulfur using Ge and Pd as modifiers is based on the reduction of the sulfates in pres ence of carbon, resulting in the formation of GeS and PdS, respectivel y. This explanation has been supported by comparing the experimental r esults with thermodynamic calculations considering different reactions for the thermal decomposition of the sulfates. Applying Ge (in KOH) a s modifier the absolute detection limit was 300 pg sulfur (e.g. LOD 30 ng mL(-1)). The significant influence of phosphates on the determinat ion of sulfur could be essentially reduced by Pd as modifier.