Toxicity measurements in concentrated water samples - Rivm

acetone eluate
Kuderna Dänisch
destillation
replenish with
test medium
Figure 3-3. The concentrate was prepared by dilution with medium after removing the acetone.
3.2.4 Replenish with test medium
residue concentrated
water sample
The residue is replenished with water (EPA medium: Freeman, 1953 and US EPA, 1985) until the
desired volume is achieved, resulting in a concentrated water sample that is suitable for ecotoxicity
testing (Figure 3-3). The water sample is usually concentrated a thousand-fold for monitoring purposes:
60 litres of water is concentrated to 60 ml. For other purposes it can be chosen to use a lower
concentration factor by replenishing the residue to a larger volume.
3.3 Effectiveness of the method
When considering application of the XAD concentration method on environmental samples, it may be
helpful to have insight into the effectiveness of the method for different kinds of chemicals. In order to
be effectively concentrated, the substances must be:
- extracted from water onto XAD;
- eluted from XAD into acetone ;
- non-volatile enough not to evaporate during distillation;
- stable enough not to break down during distillation;
- soluble enough not to exceed maximum water solubility in the concentrated sample.
Concentrating environmental water samples is almost by definition a matter of working with unknown
mixtures of micropollutants. Many factors influence the recovery of chemicals at the end of the
concentration procedure. It is therefore important to realize that it is impossible to know the exact
effect of the different operations in the concentration procedure. Variation in handling of a sample may
result in increased recovery variation. For this reason, it is important to standardize the procedure as
much as possible.
This section specifies the principles on which the method is based, which gives insight in factors
influencing the effectiveness of the method.
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