Hach DR2400 - Multiple Standard Additions

Chemical Analysis
Chemical Analysis
5940022ChemAnal.fm Page 35
Example A
Example B
Figure 10 Multiple Standard Additions — A and B
The plot for Example A illustrates an interference that becomes progressively
worse as the concentration of the standard or analyte increases. This type of
interference is uncommon and is more likely to be caused by an error or
malfunction of the procedure, reagents, or instrument. Repeat Branch B to verify
the interference.
The plot for Example B illustrates a common chemical interference that becomes
less, or even zero, as the concentration of standard or analyte increases. The
graph shows the first addition was consumed by the interference and the
remaining additions gave the correct increment of 0.2 mg/L. This could also be
the result of an error made in the standard addition. Repeat the analysis to see if
an error was made during the standard addition. For these two types of
interferences, the method is not appropriate for the sample matrix. Analyze the
sample by another method that uses a different chemistry.
Branch G Examples C and D show uniform increments between the standard
additions produced by the presence of interferences. These data points have
been plotted in Figure 11.
mL standard added mg/L standard added mg/L analyte found
001.0
0.1 0.2 1.10
0.2 0.4 1.18
0.3 0.6 1.23
mL standard added mg/L standard added mg/L analyte found
000
0.1 0.2 0
0.2 0.4 0.2
0.3 0.6 0.4
.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
A
B
mg/L STANDARD ADDEDmg/L ACTUALLY PRESENT
mg/L OBSERVED