Three 10-g samples of the homogenized tissue were placed in porcelain curcibles and dry ashed. Dry ashing serves to free the analyte from organic material and convert the arsenic present to As2O5. Samples of the discolored grass were treated in a similar manner.
Dissolving the Samples
The dry solid in each of the sample crucibles was dissolved in dilute HCl, which converted the As2O5 to soluble H3AsO4.
Reactions to Eliminate Interferences:
H3AsO4 + SnCl2 + 2HCl --> H3AsO3 + SnCl2 + H2O
H3AsO3 + 3Zn + 6HCl --> AsH3(g) + 3ZnCl2 + 3H2O
Bubble gas into collectors with silver diethyldithiocarbamate to form a colored complex compound shown below.
Measuring the Amount of Analyte
Spectrophotometer: Highly colored complex of arsenic was found to absorb light at a wavelength of 535 nm.
Calculating the Concentration
ppm = (Absorbance -.005)/0.0282
Deer 1: (0.61 - 0.005)/0.0282 = 22 ppm
Deer 2: (0.43 -0.005)/0.0282 = 15 ppm
Arsenic in the kidney tissue of animals is toxic at levels above about 10 ppm.
Grass Samples showed about 600 ppm arsenic.
Reliability of the Data
The data from these experiments could be analyzed using the statistical methods we will describe in Section 3.
Where Do We Begin?
Review of Basic Tools and Operations of Analytical Chemistry