|Harnly, James - Jim|
Submitted to: Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/15/2002
Publication Date: 2/1/2002
Citation: Ozcan, M., Akman, S., Schuetz, M., Murphy, J.R., Harnly, J.M. 2002. The spatial distribution and photometric and analytical accuracy of sn in graphite furnace atomic absorption spectrometry in the presence of sulfates and palladium. Journal of Analytical Atomic Spectrometry. 17:515-523. Interpretive Summary: This work examined the changes in the distribution of Sn atoms in a graphite furnace as a function of the sample matrix. It was found that, compared to standards in dilute acid, a sulfate sample matrix (e.g. K2SO4 or NiSO4) caused a dramatic change in distribution of the Sn atoms. This redistribution was correlated with poor estimates of the Sn concentration (as low as 30% recovery). Addition of Pd, a matrix modifier, produced an atom distribution slightly different than the dilute acid matrix but this distribution was constant even with the addition of K2SO4 or NiSO4. Molecular spectra verified the loss of Sn from the furnace (in the presence of sulfate) as SnO and SnS. This work demonstrated the utility of spatially resolved absorbance measurements for the diagnosis of matrix interferences and the utility of a Pd matrix modifier for correcting these interferences. This work is of value to researchers, analysts, and instrument manufacturers. It provides a fundamental understanding as to how these interferences come about and how continuum source atomic absorption provides the chemist with a powerful new tool for obtaining accurate determinations.
Technical Abstract: The vertical spatial distribution of Sn in the graphite furnace was determined in the presence of 0.5% HCl (standards) and 10 mg of KCl, K2SO4, and NiSO4, with and without 5 mg of Pd, using a spectrometer capable of measuring spatially resolved absorbance. An inverse gradient (decreasing concentration with increasing height in the furnace) was observed for Sn in HCl and KCl. This gradient was dramatically reversed in the presence of K2SO4 (at all pyrolysis temperatures) and NiSO4 (at pyrolysi temperatures below 900 C) and was accompanied by poor analytical recoveries. Accurate analytical recoveries and an inverse gradient were obtained for NiSO4 when a pyrolysis temperature of 900 C was used. Pd yielded inverse gradients statistically different (steeper) than those obtained with Sn Standards in HCl. The gradient for Sn in the presence of Pd was not affected by 10 mg of KCl, K2SO4, and NiSO4. Accurate analytical recoveries were obtained for Sn in Pd in all the matrices tested in this study and at all pyrolysis temperatures. The change in the Sn gradient induced by KCl, K2SO4, and NiSO4 resulted in photometric errors that are problematic for conventional, line-source AAS. Selection of the height of the viewing region within the furnace can exacerbate or improve the analytical recoveries. The constant Sn gradient established by Pd removed photometric error as an error source in the determination of Sn.