172
Sampling and Storage
Collect samples in plastic bottles. Samples may be stored up to
28 days.
Accuracy Check
Standard Solution Method
A variety of standard solutions covering the entire range of the
test are available from Hach. Use these in place of sample to
verify technique. Minor variations between lots of reagent
become measurable above
1.5 mg/L. While results in this region are usable for most
purposes, better accuracy may be obtained by diluting a fresh
sample 1:1 with deionized water and retesting. Multiply the
result by 2.
Standard Adjust
To adjust the calibration curve using the reading obtained with a
1.80-mg/L Standard Solution, press
SETUP and use the arrow
keys to scroll to the “STD” setup option. Press
ENTER to activate
the option. Then enter
1.80 to edit the standard concentration to
match that of the standard used. Press
ENTER to complete the
adjustment. See Standard Curve Adjustment in Section 1 for more
information.
Method Performance
Precision
In a single laboratory, using standard solutions of 1.00 mg/L
fluoride and two lots of SPADNS Reagent with the instrument, a
single operator obtained standard deviations of ±0.035 mg/L
fluoride.
In a single laboratory, using standard solutions of 1.00 mg/L
fluoride and two lots of SPADNS AccuVac Reagent with the
instrument, a single operator obtained standard deviations of
±0.040 mg/L fluoride.
Estimated Detection Limit (EDL)
The EDL for programs 27 and 28 is 0.05 mg/L F
-
. For more
information on derivation and use of Hach’s estimated detection
limit, see Section 1.
FLUORIDE, continued
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