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ARS Home » Northeast Area » Beltsville, Maryland (BHNRC) » Beltsville Human Nutrition Research Center » Food Composition and Methods Development Laboratory » Research » Publications at this Location » Publication #71882


item Smith, Clare
item Harnly, James - Jim

Submitted to: Journal of Analytical Atomic Spectrometry
Publication Type: Trade Journal
Publication Acceptance Date: 8/27/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: A modified two-step graphite furnace for atomic absorption spectrometry has been built and characterized which allows the selective volatilization of inorganic Fe and Fe as hemoglobin (heme Fe). The two-step furnace uses two furnaces: the first volatilizes the metal containing compounds which are then swept into a second which atomizes them, i.e. reduces them to the atomic state. With independent control of the two furnaces, the metal species of a sample can be temporally separated using a slow heating rate in the first furnace while the second furnace is maintained at a sufficiently high temperature to atomize the metals and provide accurate determinations. Heme Fe is absorbed more readily by the body than inorganic Fe. Hemoglobin is a very stable compound with a high volatility (sublimates at 200-300C for 30 s, the first furnace can be stepped to 300C for 15 s and them 2000C to produce two Fe peaks; heme Fe and inorganic Fe. These results indicate that the two-step furnace offers a rapid, easy method to quantitatively differentiate between heme and inorganic Fe.

Technical Abstract: A two-step furnace was modified by eliminating the contact between the cup furnace and the integrated contact cuvette (ICC), thus permitting independent heating of both components. Optimized cup and ICC temperatures were determined for Cd, Cr, Cu, Fe, and Pb. Efficient analyte transportation (91%), from the cup to the ICC, was observed for an ICC-cup separation of up to 3 mm. Analyte transport was aided by an apparent convective flow of Ar into the hole in the bottom of the ICC. Despite this observation, the loss of Cd and Pb from the furnace appear to be limited by diffusion. The relative sensitivity for the modified two-step furnace was approximately 50% worse than that for the same ICC with atomization from a platform. Fe in a porphyrin complex (heme Fe) was found to volatilize at approximately 300C and could be easily distinguished from non-heme Fe which volatilized at 2000C. Use of a two-stage heating step for the cup (the furnace temperature was held constant while the cup was heated to 300C and then 2000C) produced two peaks, the heme and non-heme Fe, respectively.