Branch Procedure Answer
E Check the performance of the reagents. Use a
known standard solution to do the test or use a
new fresh lot of the reagent.
If the reagents used were
defective, do Branch B again
with new reagents.
If the reagents are in good
condition, go to Branch H.
F Non-equal increments between standard
additions shows that interferences are in the
sample.
Refer to Figure 7. In Plot A and B, the four data
points are not in a straight line (linear).
Plot A shows an interference that becomes
gradually worse as the concentration of the
standard increases. This type of interference is
not common and may be caused by an error or
malfunction of the procedure, reagents or
apparatus. Do Branch B again to make sure
that an interference is present in the sample.
Plot B shows a typical chemical interference,
which becomes less or even zero as the
concentration of the standard increases. The
plot shows the first standard addition was
consumed by the interference and the
remaining additions gave the correct increase
of 25 mg/L for each additional 0.1 mL of
standard added. The interference in Plot B
could be the result of an error made in the
standard addition. Do the analysis again with a
fresh sample.
Refer to the Interferences
section of the procedure for
the steps to remove the
interferences or use a
different method that uses a
different type of chemistry.
16 English
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