Determination of Trace Selenium in High-Carbon and High-Sulfur Geological Samples by Thiol Cotton Fiber Separation-Atomic Fluorescence Spectrometry

BACKGROUND Hydride generation-atomic fluorescence spectroscopy (HG-AFS) is highly sensitive for the determination of trace selenium in geological samples. However, the complex matrix increases the analysis difficulty, especially owing to interference caused by organic carbon, complicated complexes, and coexisting ions in samples rich in organic matter and sulfides. Therefore, sample pretreatment is important. The use of conventional thiol cotton fiber (TCF) to enrich and separate selenium often leads to unstable recovery and premature saturation of the TCF when dealing with samples rich in organic matter and sulfides. OBJECTIVES To establish a method suitable for the determination of trace selenium in geological samples rich in organic matter and sulfides. METHODS For samples rich in organic matter, a double TCF column (mTCF=0.15g) was used to carry out adsorption twice. The recovery for high-sulfur geological samples could be increased either by increasing the amount of TCF (mTCF ≤ 0.2g) or reducing the sample amount. RESULTS The measurement results for the reference materials and actual samples showed that the optimized method satisfied the analysis requirements as selenium recoveries of >95.1% and >95.5% were achieved for the organic-rich and sulfide samples, respectively. Microwave digestion can effectively avoid the loss of selenium during digestion; the measured selenium content was consistent with that reported in the literature. CONCLUSIONS The improved method is suitable for geological samples rich in organic matter and sulfides, which can be used to determine trace selenium (ng/g to μg/g levels) in geological samples.