Hach DR/700 Procedures Manual page 411

LEAD,
continued
result for volume additions; see Sampling and Storage, Volume
Additions, (Section I) for more information.
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Lead Voluette Ampule Standard Solution,
50 mg/L as Pb.
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 and mix each
thoroughly.
c) Analyze each sample as described above. The lead concentration
should increase 20 µg/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 Lead Dithizone test
procedure. To obtain the most accurate results, a new calibration should
be done when a different manufacturing lot of DithiVer Metals Reagent
Powder Pillows is used.
Prepare a 5.00 mg/L lead solution by pipetting 5.00 mL of 100 mg/L Lead
Standard Solution into a 100-mL volumetric flask. Add demineralized
water to the 100-mL mark. Cap the flask and slowly invert ten times to
mix. This solution should be prepared fresh each day it is used.
Use a 4.00-mL volumetric pipet twice to pipet 8.0 mL of the 5.00 mg/L
lead solution into a 500-mL separatory funnel. Add 242 mL of
demineralized water to the funnel to make a 160 µg/L lead solution.
Perform Steps 3 through 10 of the Lead Dithizone test procedure using
the solution in the funnel.
Perform paragraph 3.2.4.1, Calibration Using Two Prepared Standards,
in the DR/700 instrument manual. For Standard 1 use the Lead test
procedure's "blank". Make the display show 0000 µg/L. For Standard 2
make the display show 0160 µg/L and use the Lead test procedure's
"prepared sample".
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