With Eriochrome cyanine R dye, dilute aluminum solutions buffered to a pH of
6.0 produce a red to pink complex that exhibits maximum absorption at 535 nm. The intensity of
the developed color is influenced by the aluminum concentration, reaction time, temperature,
pH, alkalinity, and concentration of other ions in the sample. To compensate for color and
turbidity, the aluminum in one portion of sample is complexed with EDTA to provide a blank.
The interference of iron and manganese, two elements commonly found in water when
aluminum is present, is eliminated by adding ascorbic acid. The optimum aluminum range lies
between 20 and 300 µg/L but can be extended upward by sample dilution.