Hach DR/850, Procedures Manual, Page: 74 / 460

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Estimated Detection Limit
The estimated detection limit for program #1 is 0.013 mg/L Al. For more
information on the estimated detection limit, see
Section 1 .
Interferences
Fluoride interferes at all levels by complexing with aluminum. The actual
aluminum concentration can be determined using the Fluoride
Interference Graph when the fluoride concentration is known. To use the
fluoride interference graph:
Interfering
Substance
Interference Levels and Treatments
Acidity Acidity interferes at greater than 300 mg/L as CaCO
3
. Treat sam-
ples with greater than 300 mg/L acidity as CaCO
3
as follows:
1. Add one drop of m-Nitrophenol Indicator Solution to the sample
taken in Step 3.
2. Add one drop of 5.0 N Sodium Hydroxide Standard Solution.
Stopper the cylinder. Invert to mix. Repeat as often as necessary
until the color changes from colorless
to yellow.
3. Add one drop of 5.25 N Sulfuric Acid Standard Solution to
change the solution from yellow back to colorless. Continue with
the test.
Alkalinity 1000 mg/L as CaCO
3
. Eliminate interferences from higher alkalin-
ity concentrations using the following pretreatment:
1. Add one drop of m-Nitrophenol Indicator Solution to the sample
taken in Step 3. A yellow color indicates
excessive alkalinity.
2. Add one drop of 5.25 N Sulfuric Acid Standard Solution. Stop-
per the cylinder. Invert to mix. If the yellow color persists, repeat
until the sample becomes colorless. Continue with the test.
Calcium Does not interfere.
Fluoride Interferes at all levels. See graph below.
Iron Greater than 20 mg/L.
Phosphate Greater than 50 mg/L.
Polyphosphate Polyphosphate interferes at all levels by causing negative errors and
must not be present. Before running the test, polyphosphate must
be converted to orthophosphate by acid hydrolysis as described
under the phosphorus procedures.
ALUMINUM,
continued