Hach DR/700 Procedures Manual page 332

ALUMINUM,
0.008 mg/L Al. The limit of detection was calculated as three times the
standard deviation when testing zero concentration samples (adapted
from Analytical Chemistry, 1980, 52, 2242-2249).
INTERFERENCES
The following do not interfere up to the indicated concentrations.
Alkalinity
Iron
Phosphate
Interferences from higher alkalinity concentrations can be eliminated by
the following pretreatment.
a) Add one drop of m-Nitrophenol Indicator Solution to the sample
taken in Step 1. A yellow color indicates excessive alkalinity.
b) Add one drop of 5.25 N Sulfuric Acid Standard Solution. Stopper the
cylinder. Invert to mix. If the yellow color persist, repeat until the sample
changes to colorless. Continue with the test.
Polyphosphate interferes at all levels by causing negative errors and
must not be present. Before running the test convert the polyphosphate
to orthophosphate by acid hydrolysis as described under the phosphorus
procedures.
Acidity interferes at greater than 300 mg/L as CaCO
greater than 300 mg/L acidity as CaCO
a) Add one drop of m-Nitrophenol Indicator Solution to the sample
taken in Step 1.
b) 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.
c) Add one drop of 5.25 N Sulfuric Acid Standard Solution to change
the solution from yellow back to colorless. Continue with the test.
Calcium does not interfere.
continued
1000 mg/L as CaCO
20 mg/L
50 mg/L
52-6
. Samples with
3
must be treated as follows:
3
3