Metrohm 899 Coulometer - Manual (Page 39)

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4 Coulometric titration
899 Coulometer
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4.2 Working with water standards
4.2.1 Certified water standards
For validating the instrument as a whole, integrated system, commercially
available, certified water standards with water contents of 1.00 ± 0.003
mg/g and/or 0.10 ± 0.005 mg/g should be used.
Note
The 1.0 mg/g water standard is easier to handle and therefore to be
preferred.
Table 1 Recommended sample sizes
Water standard 1.0 mg/g 0.2…2.0 g
Water standard 0.1 mg/g 0.5…5.0 g
4.2.2 Practical recommendations
For validation, it is essential to work very accurately. In order to minimize
any measurement inaccuracies that could occur, the sample preparation
and the sample processing should proceed in accordance with a defined
scheme:
1 Put on gloves (always with Karl Fischer titration).
2 Use a clean syringe.
Note
If you are working with the 0.1 mg/g water standard, then you
must use a glass syringe. If you are working with the 1.0 mg/g
water standard, then you may use either a plastic syringe or a
glass syringe.
3 Take a new ampoule of water standard and shake it briefly.
4 With a folded paper towel held between thumb and index finger,
break open the ampoule at the marking.
5 Draw approx. 1 mL of the water standard into the syringe.