Hach DR/700 Procedures Manual page 104

MOLYBDENUM, MOLYBDATE, HR, continued
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Molybdenum Voluette Ampule Standard Solution,
6+
500 mg/L Mo .
b) Use the TenSette Pipet to add 0.1, 0.2 and 0.3 mL of standard to three
25-mL samples, Mix thoroughly.
c) Analyze the spiked sample according to the above procedure. The
molybdenum concentration reading should increase by 2.0 mg/L for
each 0.1 mL addition of standard.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
Standard Solution Method
To assure the accuracy of the test, use a Molybdenum Standard Solution,
6+
10.0 mg/L Mo , listed under Optional Reagents.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched cells and two representative lots
of testing reagents. Testing 20.0 mg/L Mo concentration samples, the
standard deviation was ±0.11 mg/L Mo.
Testing zero concentration samples, the limit of detection was 0.18 mg/L
Mo. 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
Samples containing 10 mg/L copper or more will exhibit an increasing
positive interference upon standing. Read these samples as soon as
possible after the 5-minute reaction period of Step 8.
Aluminum, iron and nickel do not interfere in concentrations up to 50 mg/L.
Chromium does not interfere in concentrations up to 1000 mg/L.
-
Interference from nitrite up to 2000 mg/L as NO can be eliminated by
2
adding one Sulfamic Acid Powder Pillow in Step 4.
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