Hach DR/700 Procedures Manual page 333

ALUMINUM,
continued
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, select the vertical grid line along the
top of the graph that represents the aluminum reading obtained in
Step 14. Locate the point on the line where it intersects with the
horizontal grid line that indicates how much fluoride is present in the
sample. Extrapolate the true aluminum concentration by following the
curved lines on either side of the intersect point down to the true
aluminum concentration.
For example, if the aluminum test result was 0.7 mg/L Al and the
-
fluoride present in the sample was 1 mg/L F , the point where the 0.7
-
grid line intersects with the 1 mg/L F grid line falls between the 1.2 and
1.3 mg/L Al curves. In this case, the true aluminum content would be
1.27 mg/L.
SUMMARY OF METHOD
Aluminon indicator combines with aluminum in the sample to form a
red-orange color. The intensity of color is proportional to the aluminum
concentration. Ascorbic acid is added to remove iron interference. The
AluVer 3 Aluminum Reagent, packaged in powder form shows
exceptional stability and is applicable for fresh water samples.
DISPLAYED DR/700 VALUE (mg/L Al 3+ )
3+
mg/L AL
TRUE ALUMINUM VALUE
FLUORIDE INTERFERENCE GRAPH
52-7