Hach DR/700 Procedures Manual page 587

FORMALDEHYDE,
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Formaldehyde Voluette Ampule Standard
Solution, 4000 mg/L.
b) Use the TenSette Pipet to add 0.2 mL of standard to a 100-mL
volumetric flask. Dilute to volume with formaldehyde-free water.
Mix well. Prepare daily. This is an 8 mg/L formaldehyde
standard solution.
c) Use the TenSette Pipet to add 0.1 mL, 0.2 mL and 0.3 mL of diluted
standard (8 mg/L) to three 25-mL water samples. Mix each thoroughly.
d) Analyze each sample as described above. The formaldehyde
concentration should increase 32 µg/L for each 0.1 mL of standard added.
e) If these increases do not occur, see Standard Additions (Section I) for
more information.
Standard Solution Method
Prepare a 320 µg/L formaldehyde standard by pipetting 1.0 mL of the
8 mg/L solution from the Accuracy Check into a 50-mL mixing cylinder.
Dilute to 25.0 mL with formaldehyde-free water. Run the test directly
on this sample.
INTERFERENCES
The following may interfere when present in concentrations exceeding
levels listed below.
Acetate
Ammonium (as N)
Aniline
Bicarbonate
Calcium
Carbonate
Chloride
Copper
Cyclohexylamine
Ethanolamine
Ethylenediamine
Glucose
Glycine
continued
1000 mg/L
10 mg/L
10 mg/L
1000 mg/L
3500 mg/L
500 mg/L
5000 mg/L
1.6 mg/L
250 mg/L
33 mg/L
1.5 mg/L
1000 mg/L
1000 mg/L
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