Determination of selenium in biological materials with platform furnace atomic-absorption spectroscopy and Zeeman background correction
The presence of phosphate and iron provides a spectral interference for the determination of selenium at its primary resonance line at 196.0 nm that is avoided by using Zeeman background correction. Good quality pyrolytic graphite tubes, platform atomisation and integrated absorbance readings provide an acceptable quantitative environment for selenium and permit most analyses to be performed against a simple calibration graph using selenium in a nickel matrix modifier. Remaining problems appear to relate to loss of selenium prior to atomisation in the presence of certain matrices, notably the combination of sodium and sulphate. Charring in the presence of oxygen did not improve the analytical situation, nor did the use of silver, molybdenum or copper as a matrix modifier. We found a 2σ detection limit of 28 pg and a sensitivity of about 25 pg per 0.0044 As (A = absorbance units), expressed as characteristic amount. A preliminary direct method is presented for selenium in urine, with nickel, nitric acid and magnesium nitrate present, with a detection limit in urine of about 10 µg 1–1.