2.3. Assessment of Fe and Cr levels in tissues
Tissue levels of total Cr and Fe were measured in 5 animals per dose group.
Samples were shipped frozen to Brooks Rand Laboratories where approximately
100 mg of tissue was digested in nitric acid in a controlled microwave digestion
program. Samples were then brought to a final volume of 8 mL with deionized
water. Analysis was performed using EPA Draft Method 1638 (modified) using
inductively coupled plasma-mass spectrometry (ICP-MS) with Dynamic Reaction
Cell (DRC™) technology. Digested samples were analyzed utilizing internal standardization
with rhodium. This method incorporates ionization of the sample in
an inductively-coupled RF plasma, with detection of the resulting ions by mass
spectrometer on the basis of their mass-to-charge ratio. Results were presented
for total Fe in duodenum and liver and total Cr in the RBCs and plasma. The limit
of detection was 0.02 lg Cr/g tissue. Iron levels were simultaneously measured in
these tissue samples, and the limit of detection was 0.2 lg Fe/g tissue.