Hach DR/700 Procedures Manual page 368

CADMIUM,
continued
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Cadmium Voluette Ampule Standard Solution,
25 mg/L Cd.
b) Use the TenSette Pipet to add 0.1 mL, 0.2 mL, and 0.3 mL of
standard, respectively, to three 250-mL samples. Mix each thoroughly.
c) Analyze each sample as described above. The cadmium
concentration should increase 10 µg cadmium/L for each 0.1 mL of
standard added.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
CALIBRATION
The DR/700 must be calibrated in order to use the Cadmium Dithizone
test procedure. To obtain most accurate results, perform a new
calibration when a new lot of DithiVer Metals Reagent Powder Pillows
is used.
To calibrate:
a) Prepare a 5.0 mg/L cadmium solution by pipetting 5.0 mL of 100-mg/L
Cadmium Standard Solution into a 100-mL volumetric flask.
b) Dilute the solution in the flask to the mark with demineralized water.
c) Cap the flask and invert 10 times to mix. Make this solution fresh
each day it is needed.
d) Pipet 4.0 mL of the 5.0-mg/L cadmium solution into a 500-mL
separatory funnel.
e) Add 246 mL of demineralized water to the funnel to make an 80-µg/L
cadmium solution.
f) Perform Steps 1-11 if the Cadmium Dithizone procedure, using the
80-µg/L solution in Step 4.
g) Perform paragraph 3.2.4.1, Calibration Using Two Prepared
Standards, in the DR/700 Instrument Manual.
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