Determination of selenium in acid digested marine samples by electrothermal atomic absorption spectrometry with continuum source background correction and nickel as a chemical modifier

Abstract

Severe effects on the selenium signal owing to phosphate decomposition products are found when a deuterium arc is used as the continuum light source for background correction in the determination of selenium by electrothermal atomic absorption spectrometry. Hence, this system does not correct effectively for spectral interferences. In order to remove the severe negative interference due to phosphate decomposition products, various electrothermal atomizers were compared. An uncoated graphite tube with a L'vov platform inserted was found to be the most effective atomizer. The effect of nickel as a chemical modifier was also studied in relation to the presence of varying amounts of phosphorus in the sample solution. An amount of 50 µg of nickel (in an injection volume of 20 µl) was found to be sufficient for sample solutions containing moderate levels of phosphorus (e.g., <2 µg of phosphorus in a 20 µl injection solution), as found in, for example, National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1566 Oyster Tissue; 100 µg of nickel are recommended for stabilizing selenium if higher levels of phosphorus are present. The procedure used and the results obtained are as follows: biological samples were digested with HNO3–HClO4; calibration was carried out using the standard additions procedure; measurement was made using the peak heights; precision of 3.5% for NIST SRM Oyster Tissue with a measured concentration of 1.95 µg g–1 within the certified range (2.1 ± 0.5 µg g–1) was obtained; the method was applied to eight different marine biological tissue samples from the International Council for the Exploration of the Sea intercalibration exercise (1984, 1987).