Storage is a huge task, in particular if long-term storage is needed. There are
different processes attacking the sample material over time comprising microbial
transformation, heat and light induced changes as well as abiotic oxidation. Therefore, some protective measures need to be taken. In order to avoid alteration due to
(sun)light and thermal stress, the samples should be stored in the dark and at low
temperatures (e.g. 4
C or deep frozen). If anaerobic sample material needs to be
stored (e.g. river sediments) anoxic conditions must be stabilized e.g. by addition of
inert gas such as N 2 .
The most critical point in storage of samples for organic analyses is to avoid
microbial transformation of the matrix and, in particular, of the analytes. Biotic
transformation is induced by both the microorganisms themselves and the
corresponding extracellular enzymes. Hence both need to be reduced or eliminated,
the microorganism (dominantly bacteria) and the enzyme activity. There are several
methods for such a sterilization process that exhibit different sterilization strength,
but they induce also changes of the sample material to a varying extent. The methods
cover physical mechanisms such as γ-ray irradiation or autoclavation, but also
chemical poisoning e.g. with mercury chloride HgCl 2 or sodium azide NaN 3 .
However, beside possible changes of the sample structure or integrity, also the
duration for which the preservation is kept needs to be considered. Some examples
of poisoning and the resulting maximum storage time for different target analytes in
water samples are given in Table 3.1.
General Note
Storage and pre-preparation of sample material need some specific measures.
Best practice is to perform the main analytical procedure immediately after
sampling.
Table 3.1 Some examples of preservation and the resulting maximum storage time
Target analytes
Sample
vessel
Preservation
Maximum
storage time
Pesticides
(organochlorine)
Glass
1 mL of a 10 mg/mL HgCl 2 or adding of
extraction solvent (500 mL of water sample)
7 days, 40 days
after extraction
Pesticides
(organophosphorus)
Glass
1 mL of a 10 mg/mL HgCl 2 or adding of
extraction solvent (500 mL of water sample)
14 days,
28 days after
extraction
Phenolic
compounds
Glass
Cool to 4
C add H 2 SO 4 to pH < 2 (50 mL of
water sample)
28 days
3.1 Sample Storage and Pre-preparation
17
different processes attacking the sample material over time comprising microbial
transformation, heat and light induced changes as well as abiotic oxidation. Therefore, some protective measures need to be taken. In order to avoid alteration due to
(sun)light and thermal stress, the samples should be stored in the dark and at low
temperatures (e.g. 4
C or deep frozen). If anaerobic sample material needs to be
stored (e.g. river sediments) anoxic conditions must be stabilized e.g. by addition of
inert gas such as N 2 .
The most critical point in storage of samples for organic analyses is to avoid
microbial transformation of the matrix and, in particular, of the analytes. Biotic
transformation is induced by both the microorganisms themselves and the
corresponding extracellular enzymes. Hence both need to be reduced or eliminated,
the microorganism (dominantly bacteria) and the enzyme activity. There are several
methods for such a sterilization process that exhibit different sterilization strength,
but they induce also changes of the sample material to a varying extent. The methods
cover physical mechanisms such as γ-ray irradiation or autoclavation, but also
chemical poisoning e.g. with mercury chloride HgCl 2 or sodium azide NaN 3 .
However, beside possible changes of the sample structure or integrity, also the
duration for which the preservation is kept needs to be considered. Some examples
of poisoning and the resulting maximum storage time for different target analytes in
water samples are given in Table 3.1.
General Note
Storage and pre-preparation of sample material need some specific measures.
Best practice is to perform the main analytical procedure immediately after
sampling.
Table 3.1 Some examples of preservation and the resulting maximum storage time
Target analytes
Sample
vessel
Preservation
Maximum
storage time
Pesticides
(organochlorine)
Glass
1 mL of a 10 mg/mL HgCl 2 or adding of
extraction solvent (500 mL of water sample)
7 days, 40 days
after extraction
Pesticides
(organophosphorus)
Glass
1 mL of a 10 mg/mL HgCl 2 or adding of
extraction solvent (500 mL of water sample)
14 days,
28 days after
extraction
Phenolic
compounds
Glass
Cool to 4
C add H 2 SO 4 to pH < 2 (50 mL of
water sample)
28 days
3.1 Sample Storage and Pre-preparation
17