1-18
5. Compare the pH values of your analyzed sample with the reagent
blank.
6. If there is no difference in the pH values of your analyzed sample and
the reagent blank, then pH interference is not the problem. Follow the
Accuracy Check given in the procedure to more clearly identify the
problem.
7. If there is a significant difference between the values of your analyzed
sample and the reagent blank, adjust the sample pH to within the
optimum pH test range, or if none is given, to the value of the reagent
blank before analysis on all future determinations. Use the appropriate
acid, usually nitric acid, to lower the pH, and use the appropriate base,
usually sodium hydroxide, to raise the pH.
8. Analyze the sample as before.
Interference From Stray Light
Typical indoor lighting permits the DR/700 to operate with the cell
compartment cover open. In bright sunlight, it may be necessary to
close the cell compartment cover. If a 25-mL cell is used in the
procedure, transfer 10 mL of the solution to a 10-mL cell. If the 10-mL
cell is used for the blank, another 10-mL cell must be used for the
sample.
LABORATORY PRACTICE
Boiling Aids
Boiling is included as a necessary step in some procedures. It may be
convenient to use a boiling aid such as boiling chips, Cat. No. 14835-31,
to reduce bumping. Bumping is caused by the sudden, almost explosive
conversion of water to steam as it is heated. Bumping may cause sample
loss or a hazardous condition and should be avoided.
All boiling aids used should be checked to verify they will not
contaminate the sample. Boiling aids (except glass beads) should not be
used again. Loosely covering the sample during boiling will prevent
splashing, reduce the possibility of contamination and minimize sample
loss.
Filtration of Samples
Filtering is the process of separating particles from the sample by using
a medium, generally filter paper, to retain particles but allow the
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