Development of Karl Fischer Reagents

Chapter I: Basic Knowledge
(2) Syringes
These are used for most liquid samples. Glass syringes are most commonly
used, however plastic products (disposable) are also convenient. The most
commonly used commercial products are 1, 2, 5 and 10ml syringes. General
procedures for using syringes are described below.
a) After carefully drying the syringe (figure 6), flush it two or three times with
small amounts of the sample. Then draw in the required amount of the
sample.
b) Attach a piece of silicon rubber to the needle and weigh the syringe.
c) Remove the silicon rubber and insert the syringe needle through the
stopper attached to the side valve of the titration cell (Figure 8). Inject the
sample.
d) Pull out the syringe needle and weigh it accurately with the piece of
silicon rubber attached to the needle.
e) The difference between the two weights is the weight of the sample.
Cap nut
Figure 8: Stopper
Silicon washer
Common fitting
(3) Pipettes
Because a stopper cannot be used with a pipette, the side stopper (or
sample injection stopper) must be removed. With the stopper removed the
experiment is exposed to the air and the results must be corrected for the
infiltration by atmospheric moisture by conducting a blank test for the same
period of time that the flask was open. The method is unsuitable, therefore,
for the coulometric titration used to measure trace amounts of moisture.
The weight of the sample is determined by separate measurement of the
relative gravity (or density). We recommend the use of syringes wherever
possible.
(4) Dropper bottle
Dropper bottle (Figure 9) are used for water or for samples with a high
moisture content. They are especially convenient for measuring water when
determining the titer of Karl Fischer Reagent SS-Z (or SS) using water. With
commercially available products, the pipettes produce droplets of about
30mg each.
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