Hach-Lange HQD - Gel filled ORP_Redox electrode MTC - Manual (Page 8)

8 DOC272.53.80033
1. Fill a 10 ml
burette with a
standard titrant
solution with a
normality that is 5-10
times that of the
sample.
2. Connect the
electrode to the
meter.
3. Pipet a 50 mL
sample into a
150-mL beaker. Stir
with a magnetic
stirrer throughout the
titration.
4. Begin by adding
titrant in 0.5 - 1 mL
increments,
recording the
potential after each
addition. Near the
end point, when
large potential
changes appear, add
increments of 0.1 -
0.2 mL. Continue the
titration 3-4 mL past
the end point.
5. Plot the
electrode potential
versus volume of
added titrant and fit a
smooth curve
through the points.
The end point is the
point of inflection
(the point of greatest
slope).
6. Calculate the
normality of the
sample, N
x
, in
equivalents per liter:
N
x
= (V
t
x N
t
) / V
x
where:
N
t
= normality of
titrant (Eq/L)
V
t
= volume of titrant
at end point (mL)
V
x
= Volume of
sample (mL)