Chemical Analysis
Chemical Analysis
Page 34
5940022ChemAnal.fm
If the results using deionized water give the expected increments (as they did in
the example above), go to Branch C.
If the results using deionized water do not give the expected increments, the
problem may lie with another part of the procedure; go to Branch D.
Branch C If interferences are present, the correct results may still be
approximated by using multiple standard additions to the sample. Follow the
procedure outlined in Branch B, substituting sample water for the
deionized water.
If the increase in the mg/L of analyte found is uniform for each standard
addition increase (ex. 0.1, 0.1, and 0.1), go to Branch G.
If the increases are not uniform (i.e., 0.1, 0.08, and 0.05), go to Branch F.
Branch D Carefully re-read the instructions for the test.
• Are the correct reagents used in the correct order?
• Is the correct program number selected?
• Is the glassware precise enough?
• Have the reactions been timed properly?
If the procedure technique was incorrect, repeat Branch B.
If the procedure technique was correct, go to Branch E.
Branch E Check the reagent performance by either obtaining a fresh lot of
reagent or by using a known standard to run the test. Make sure the color
development time given in the procedure is the same as that required for the
reagent in question.
If a reagent is defective, repeat Branch B with new reagents.
If the reagents are good, go to Branch H.
Branch F Examples A and B show non-uniform increments between the
standard additions produced by the presence of interferences. These data points
have been plotted in Figure 10.
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
These data show several points:
• The standard added to the deionized water was completely recovered. Therefore, the
chemicals, instrument, procedure/technique, and standards are working correctly.
• The standard added to the original sample was not completely recovered; therefore, the
sample contains an interference.
• Analyses done on the sample will be incorrect. The sample must be pre-treated to remove
interferences.
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