ISO 3696 Water for analytical laboratory use - Specification and test methods
5 Sampling
A representative sample of the material of not less than 2 litres shall be taken from the bulk for the purpose of examination in accordance with this specification.
NOTE This sample is not used for measurements of conductivity on grade 1 and grade 2 water (see 7.2.2.1).
The sample shall be placed in a suitable, clean, airtight container, reserved solely for water samples, which shall be of such a size that it is completely filled by the sample. Care shall be taken to avoid the risk of contaminating the contents in any way.
Aged containers (i.e. containers boiled for at least 2 h in a solution of hydrochloric acid, c(HCl) ≈ 1 mol/l, then twice for 1 h in distilled water) made of borosilicate glass can be used as well as suitable inert plastics containers (for example polyethylene or polypropylene), but it is essential to establish that the sample is unaffected by storage therein, particularly in respect of oxidizable matter and absorbance.
6 Storage
Contamination of water during storage may arise principally from dissolution of soluble constituents from glass or plastics containers or absorption of atmospheric carbon dioxide and of any other impurities present in the laboratory atmosphere.
For this reason, the storage of grade 1 and grade 2 water is not recommended, the water being prepared, as required, for immediate use.
Nevertheless, grade 2 water may be prepared in reasonable quantity and stored in suitable, inert, clean, airtight, full containers which have been thoroughly pre-rinsed with water of similar grade.
The storage of grade 3 water presents little problem, but the containers and storage conditions should be the same as those used for the storage of grade 2 water.
It is recommended that any storage container be reserved exclusively for the storage of a particular grade of water.
