Capability and limitations of the determination of sulfur in inorganic and biological matrices by total reflection X-ray fluorescence spectrometry

Abstract

The capability and limitations of TXRF were explored for the determination of the light element sulfur in inorganic and biological samples. The recovery rates of sulfur were measured with tungsten L-radiation in the dry residues of various sulfates and sulfur containing amino acids with a sulfur concentration ranging from 0.5 to 20 mg/l. Furthermore, the surface topography of the dry residues of the samples was investigated by scanning electron microscopy (SEM) and their thickness profiles were recorded by an Alpha-Step. The results show that the reliable determination of sulfur in inorganic samples depends on the cation involved. Alkali sulfates tend to form bulky residues which disturb the determination of sulfur distinctly due to absorption effects of the soft sulfur K radiation. In this case the use of smoothing detergents like 1% HF, 1% malic acid and 2% hydrazine hydrate is necessary for the determinations with reasonable accuracy (tolerance range: ±10% of the recovery rate). The results for the biological samples measured agree well with the expected values. The investigations lead to the conclusion that TXRF combined with a proper sample preparation is well suited for the determination of sulfur in samples of various matrices in a wide range of concentrations.