Processing the simple: Defining Replicate Samples
Three 10-g samples of the homogenized tissue from each deer were placed in porcelain crucibles.
Doing Chemistry: Dissolving the samples
To obtain an aqueous solution of the analyte for analysis,
it was necessary to dry ash the sample in air to convert its organic matrix to carbon dioxide and water.This process involved heating each crucible and sample cautiously over an open flame until the sample stopped smoking.The crucible was then placed in a furnace and heated at 555C for 2 hours.Dry ashing served to free the analyte from organic material and convert it to arsenic pentoxide.The dry solid in each sample crucible was then dissolved in dilute HCl, which converted the As2O5 to soluble H3AsO4
Eliminating Interferences
Arsenic can be separated from other substances the might interfere in the analysis by converting it to arsine,AsH3,a toxic,colorless gas that is evolved when a solution of H3AsO3 is treated with zinc.The solutions resulting from the deer and grass samples were combined with Sn2+ , and a small amount of iodide ion was added to catalyze the reduction of H3AsO4 to H3AsO3 According to the following reaction: H3AsO4 + SnCl2 + 2HCL-> H3AsO3 + SnCl4 + H2O
the H3AsO3 was then converted to Ash3 by the addition of zinc metal as fllows:
H3ASO3 + 3Zn + 6HCL -> AsH3(g) + 3ZnCl2 + 3H2O
The entire reaction was carried out in flasks equipped with a stopper and delivery tube so that the arsine could be collected in the absorber solution, as shown in Figure 1F-1. The arrangement ensured that interferences were left in the reaction flask and that only arsine was collected in the absorber in special transparent containers called cuvettes.