Metrohm 851 Titrando - Manual (Page 44)

4.2 Working with water standards
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851 Titrando
4.2 Working with water standards
4.2.1 Certified water standards
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 for validat-
ing the instrument as a whole, integrated system.
NOTE
The 1.0 mg/g water standard is easier to handle and therefore to be
preferred.
Table 1 Recommended sample size ranges
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 (as 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.