Storage, Transport and Preservation of Pore Water

In this section, the vessels in which the pressed or centrifuged pore water is kept until the time for analysis arrives will be briefly discussed. In Section 3.4 it will also be considered, in coimec-tion with the analytical methods, how much time one may allow to pass between pore water preparation and analysis. Hence the decision depends on whether immediate analysis is necessary, or whether the analyses can be made at a later time, provided that an appropriate preservation of the material has been accomplished. 

Bottles made of polyethylene have proven to be quite useful for the storage of filtered pore water samples. In most cases the disposable 20 ml PE-bottles which are used in scintillation measure- 

Only the alkali-metals, sulfate, and the haloge-nides do not require any preservation of the samples prior to their analytical measurement at a later date. Otherwise, pore water samples that are not to be analyzed immediately can be preserved with regard to some dissolved substances, allowing a delayed analysis. 

The concentrations of most cations - as long as different valences of iron, for instance, are not to be determined - are measurable after a longer period of time when the samples pH is lowered by the addition of acid (mostly HNO3) to a value of at least pH 2 or pH 3. Care should be taken that a sufficient amount of suprapur quality acid is added. The required amounts can vary considerably depending on the alkalinity of the sample. Usually, concentrated acid will be used in order to prevent uimecessaiy dilution of the sample. It is also important that the sample has been previously passed through a filter of 0.1 - 0.2 pm pore-size, since the acid will dissolve all particles (and certainly the colloids that pass the filter as well). 

As for the substances that are altered in their concentration by microbial activity, the toxifi-cation of sample is recommended. Mercury (II) salts are not very much favored since the handling of these extremely toxic substances - which are toxic also to man - requires special precaution measures. Chloroform is banned from most laboratories because it is considered as particularly carcinogenic. Thus, only the solvent TTE (trifluorotrichloro-ethane) remains which is frequently used in water analyses. The addition of one droplet usually suffices since only a small but sufficient proportion dissolves whereas the rest 

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