42-29
NICKEL, continued
Testing zero concentration samples, the limit of detection was 0.013 mg/L
Ni. 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
Cobalt, copper and iron interferences can be overcome by adding one or
more additional Nickel 1 Reagent Powder Pillows in Step 2. The
tolerance limits of these interferences are shown in the following table:
Table 1. Tolerance Limits
Number of Nickel Concentration of interfering substance (mg/L)
1 Pillows
needed Cobalt Copper Iron
1 1 10 20
2 7 16 65
3 13 22 110
4 18 28 155
5 25 35 200
A preliminary acid digestion is required to determine any suspended or
precipitated nickel and to eliminate interference by organic matter. To
eliminate this interference or to determine total recoverable nickel
perform the EPA approved digestion in Digestion (Section I).
Highly buffered samples or extreme sample pH may exceed the
buffering capacity of the reagents and require sample pretreatment; see
Interferences, pH (Section 1).
SUMMARY OF METHOD
Nickel ion reacts with heptoxime to form a yellow-colored complex
which is then extracted into chloroform to concentrate the color and
enable a more sensitive determination. Chelating agents are added to the
sample to overcome the interferences caused by cobalt, copper and iron.
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