Hach DR/850 - Page 239

239
Accuracy Check
Standard Additions Method
a) Fill three 25-mL mixing cylinders with 25 mL of sample.
b) Snap the neck off a Nitrate Nitrogen Ampule Standard,
500 mg/L nitrate nitrogen.
c) Use the TenSette Pipet to add 0.1, 0.2, and 0.3 mL of
Nitrate Nitrogen Standard Solution to the three samples.
Stopper and
mix thoroughly.
d) For AccuVac analysis, transfer the solutions to clean, dry
50-mL beakers. For analysis with powder pillows, transfer
only 10 mL of solution to clean, dry sample cells.
e) Analyze each sample as described above. The nitrate
nitrogen (NO
3
-
-N) concentration should increase 2.0 mg/L
for each 0.1 mL of standard added.
f) If these increases do not occur, see Standard Additions
(Section 1) for more information.
Standard Solution Method
Use a Hach Nitrate-Nitrogen Standard Solution, 10.0 mg/L NO
3
-
-
N, listed under Optional Reagents as the sample and perform the
procedure as described above.
Standard Adjust
To adjust the calibration curve using the reading obtained with
the 10.0-mg/L standard solution, press the
SETUP key and scroll
(using the arrow keys) to the STD setup option. Press
ENTER to
activate the standard adjust option. Then enter
10.0 to edit the
standard concentration to match that of the standard used. Press
ENTER to complete the curve adjustment. See Section 1, Standard
Curve Adjustment for more information. If you are using a
reagent blank correction, the blank correction should be entered
before the Standard Adjust value is entered.
Method Performance
Precision
In a single laboratory using standard solutions of 25.0 mg/L
nitrate nitrogen (NO
3
-
-N) and two representative lots of reagent
with the instrument, a single operator obtained a standard
deviation of +
0.3 mg/L nitrate nitrogen for program #50 and ±1.7
mg/L nitrate nitrogen for program # 51.
NITRATE, High Range, continued