Hach DR/850, Руководство по процедурам, Страница: 173 / 460

173
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:
SPADNS Reagent contains enough arsenite to eliminate
interference up to 5 mg/L chlorine. For higher chlorine levels,
add one drop of Sodium Arsenite Solution to 25 mL of sample for
each 2 mg/L of chlorine.
To check for interferences from aluminum, read the concentration
one minute after reagent addition, then again after 15 minutes.
An appreciable increase in concentration suggests aluminum
interference. Waiting two hours before making the final reading
will eliminate the effect of up to 3.0 mg/L aluminum.
Most interferences can be eliminated by distilling the sample
from an acid solution as described below:
a) Set up the distillation apparatus for the general purpose
distillation. See the Hach Distillation Apparatus Manual.
Turn on the water and make certain it is flowing through
the condenser.
b) Measure 100 mL of sample into the distillation flask.
Add a magnetic stirring bar and turn on the heater power
switch.
Turn the stir control to 5.
c) Cautiously measure 150 mL of StillVer Distillation
Solution (2:1 Sulfuric Acid) into the flask. If high levels
of chloride are present, add 5 mg silver sulfate for each
mg/L chloride present.
Substance Concentration Error
Alkalinity (as CaCO
3
) 5000 mg/L -0.1 mg/L F
-
Aluminum 0.1 mg/L -0.1 mg/L F
-
Chloride 7000 mg/L +0.1 mg/L F
-
Iron, ferric 10 mg/L -0.1 mg/L F
-
Phosphate, ortho 16 mg/L +0.1 mg/L F
-
Sodium Hexametaphosphate 1.0 mg/L +0.1 mg/L F
-
Sulfate 200 mg/L +0.1 mg/L F
-
FLUORIDE,
continued