Metrohm 899 Coulometer - Manual (Page 41)

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4 Coulometric titration
899 Coulometer
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If you have connected a balance to the Coulometer, you may trans-
mit the sample size directly from the balance.
16 The next determination can be started as soon as the determination
has been finished and the coulometer cell has been conditioned (drift
stable) again.
4.3 Sample addition
This chapter contains a few notes concerning sample addition. A com-
plete description of this topic is not possible here. Further notes can be
found in the publications from the reagent manufacturers and in the fol-
lowing Metrohm Application Bulletins:
Bulletin No. Title
No. 142 Karl Fischer water content determinations in gaseous samples
No. 145 The determination of small water contents in plastics
No. 209 Water content determinations in insulating oils, hydrocarbons and their
products
No. 273 Validation of KF coulometers according to GLP / ISO 9001
4.3.1 Size of the sample size
The sample weight should be small in order to be able to titrate as many
samples as possible in the same electrolyte solution and in order to keep
the titration time short. However, ensure that the sample contains at least
50 µg of H
2
O. The following table provides clues for the sample size.
Table 2 Recommended sample sizes
Content of the sample Sample size H
2
O, to be determined
(Water content)
10000 ppm = 1% 10 mg…100 mg 100 µg…1000 µg
1000 ppm = 0.1% 100 mg…1 g 100 µg…1000 µg
100 ppm = 0.01% 1 g 100 µg
10 ppm = 0.001% 5 g 50 µg