Hach DR/700 Procedures Manual page 655

ZINC,
continued
c) Analyze each sample as described above. The zinc concentration
should increase 0.1 mg/L for each 0.2 mL of standard added.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
Standard Solution Method
Prepare a 0.5 mg/L zinc standard solution by diluting 0.50 mL of zinc
standard solution, 100 mg/L as Zn, to 100 mL with demineralized water.
Prepare this solution daily.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two prepared solutions,
using one DR/700, matched sample cells and two representative lots of
testing reagents. Testing 0.80 mg/L Zn concentration samples, the
standard deviation was ±0.0068 mg/L Zn.
Testing zero concentration samples, the limit of detection was
0.022 mg/L Zn. 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 may interfere when present in concentration exceeding
those listed below:
Aluminum
Cadmium
Copper
Iron (ferric)
Manganese
Nickel
Large amounts of organic material may interfere. Perform the mild
digestion (Section I), to eliminate this interference.
Highly buffered samples or extreme sample pH may exceed the
buffering capacity of the reagents and require sample pretreatment; see
Interferences, pH (Section I).
6 mg/L
0.5 mg/L
5 mg/L
7 mg/L
5 mg/L
5 mg/L
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