User Guide

19
13.Immerse the probe tip into the sample
and make sure the platinum electrodes
are submerged.
14. Dispense 5 mL of titrant into the bea-
ker.
15.Continue dispensing titrant into the
beaker in small increments. Record the
display reading that corresponds exactly
to the mL of titrant added. Record at
least 3 points before and 3 points after
the End Point.
16. Construct a titration graph.
17.Draw a best-fit line through each set of points. The End
Point is determined
by the intersection of
the two best lines
through the points.
18. Read the volume
of titrant used until
the End Point, this is
mL zero.
Note: Standard Iodine is subjected to a normal degradation and
this could lead to an increasing of the End Point under the
same measurement conditions. Blank titration compensates
for standard iodine degradation. Discard a standard iodine
solution if the End Point is grater than 8 mL and repeat the
procedure with new standard iodine.
Sample titration
19.Refill the automatic burette to the zero mark.
20. Use a 100 mL volumetric pipet to transfer 100 mL of
sample to a 250 mL beaker and add about 100 mL chlo-
rine free water.
21.Add exactly 2 mL of the standard 0.00564N PAO solu-
tion (HI 70466) to the beaker and swirl to mix. Add 1 mL
of pH 4 acetate buffer (HI 70467) and one spoon of
potassium iodide from the bottle (HI 70468).