Hach DR2400 - Multiple Standard Additions - C and D

Chemical Analysis
Chemical Analysis
Page 36
5940022ChemAnal.fm
Example C
Example D
Figure 11 Multiple Standard Additions — C and D
The plot for Example C illustrates a common interference with a uniform effect
on the standard and the substances in the sample. The four data points form a
straight line that may be extended back through the horizontal axis. The point
where the line meets the axis can be used to determine the concentration of the
substance you are measuring.
In this example, the first analysis gave 0.4 mg/L. After extrapolating the line to
the horizontal axis, the graph shows the result should be much closer to the
correct result: 0.8 mg/L.
The plot for Example D illustrates a problem for the analyst. The increments are
uniform and the recovery of the standard is complete. The result of the first
analysis is 0 mg/L and the extrapolates back through 0 mg/L. If interferences
are known to be present, the interferences may be present in an amount equal to
the substance in question, preventing the analyst from finding the substance.
This would be an uncommon situation.
mL standard added mg/L standard added mg/L analyte found
000.4
0.1 0.2 0.5
0.2 0.4 0.6
0.3 0.6 0.7
mL standard added mg/L standard added mg/L analyte found
000
0.1 0.2 0.2
0.2 0.4 0.4
0.3 0.6 0.6
.6.4.20.2.4.6.81.01.21.4
.2
.4
.6
.8
1.0
1.2
1.4
.8
1.6
1.8
C
D
mg/L OBSERVED
mg/L STANDARD ADDEDmg/L ACTUALLY PRESENT