Hach DR/700 Procedures Manual page 342

ALUMINUM,
Table 1. Common Interferences with the Eriochrome Cyanine R Method
Constituent
Acidity
Alkalinity
2+
Ca
-
Cl
6+
Cr
2+
Cu
2+
Fe
3+
Fe
-
F
Hexametaphosphate 0.1 mg/L as PO
2+
Mg
2+
Mn
-
NO
2
-
NO
3
pH
3-
PO (ortho)
4
2-
SO
4
2+
Zn
A sample pH between about 4.9 and 7.5 causes dissolved aluminum to
partially convert to colloidal and insoluble forms. This method
measures much of that hard-to-detect aluminum without any pH
adjusting pretreatment as is necessary in some other methods.
Polyphosphate interference can be reduced by converting polyphosphate
to orthophosphate using the following steps:
a) Rinse a 50-mL mixing graduated cylinder and a 125-mL erlenmeyer
flask containing a magnetic stir bar with 6 N Hydrochloric Acid. Rinse
again with demineralized water. These rinses will remove any
aluminum present.
Note: Rinse two erlenmeyer flasks if a reagent blank is used; see Step b below.
b) Measure 50 mL of demineralized water into the 125-mL erlenmeyer
flask using the graduated cylinder. This is the reagent blank. Because of
the test sensitivity, this step must be done only when any of the reagents
continued
Concentration
0-62 mg/L as CaCO
0-750 mg/L as CaCO
0-1000 mg/L as CaCO
0-1000 mg/L
0.2 mg/L
2 mg/L
0-4 mg/L
0-4 mg/L
see Table 2
3-
4
0-1000 mg/L as CaCO
0-10 mg/L
0-5 mg/L
0-20 mg/L
2.9-4.9
7.5-11.5
4 mg/L
0-1000 mg/L
0-10 mg/L
52-16
Error
0%
3
0%
3
0%
3
0%
-5% of reading
-5% of reading
+ mg/L Fe
+ mg/L Fe
-5% of reading
0%
3
0%
0%
0%
0%
0%
-5% of reading
0%
0%
2+
0.0075
X
3+
0.0075
X