Hach DR/700 Procedures Manual page 512

FLUORIDE,
SAMPLING AND STORAGE
Samples may be stored in glass or plastic bottles for at least seven days
when cooled to 4 °C (39 °F) or lower. Warm samples to room
temperature before analysis.
ACCURACY CHECK
Standard Solution Method
A variety of standard solutions covering the entire range of the test is
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
demineralized water and retesting. Multiply the result by 2.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched sample cells and two
representative lots of reagent. Testing 2.00 mg/L F
solutions, the standard deviation was ±0.03 mg/L F
Testing zero concentration samples, the limit of detection was 0.04 mg/L
-
F . 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).
Using two representative lots of AccuVacs, the standard deviation was
-
±0.04 mg/L F and the limit of detection was 0.06 mg/L F
INTERFERENCES
This test is sensitive to small amounts of interference. Glassware must
be very clean. Repeating the test with the same glassware is
recommended to ensure that results are accurate.
The following substances interfere to the extent shown:
Alkalinity (as CaCO
Aluminum
Chloride
Iron, ferric
Phosphate, ortho
continued
Concentration
) 5000 mg/L
3
0.1 mg/L
7000 mg/L
10 mg/L
16 mg/L
57-6
-
concentration
-
.
-
.
Error
-
-0.1 mg/L F
-
-0.1 mg/L F
-
+0.1 mg/L F
-
-0.1 mg/L F
-
+0.1 mg/L F