Environmental Sampling Techniques - Fundamentals of Environmental Sampling and Analysis - page 74

hydrocarbons, pesticides, and base/neutral/acid extractable organics) have only
7 days of permissible storage time until sample pretreatment. Only samples for
hardness and general metals can be stored for up to 6 months after the addition of
HNO 3 to pH < 2.

Practical tips

The guidelines on preservation appear to be tedious, but understanding the
physicochemical and biological mechanisms behind various preservation and
storage requirements will help you make more sense.
Prior to sample transport, packaged samples must be kept in ice at 2-6 Cin
insulated coolers. ''Wet'' ice (frozen water) should be double-bagged to
prevent water damage from melting ice. The ''blue ice,'' a synthetic glycol
packaged in plastic bags and frozen, is less effective. Dry ice is not
recommended either, because it freezes samples and causes the containers
to break. When samples are kept frozen in a freezer, fill containers only 90%
full to avoid container breakage.
The MHTs are the ''rules'' of regulatory importance. Do not take chances
and violate the rules if the data will have to sustain legal challenges! In other
cases, while exceeding the holding time does not necessarily negate the
veracity of analytical results, it causes ''flagging'' of any data not meeting all
of the specified acceptance criteria (EPA, 1997).
MHTs, for the most part, are not based on rigorous scientific evaluation.
In research labs with limited resources, if recovery can be justified in a
spiked sample conducted parallel to the study, results could be acceptable
in the scientific community. The general consensus among environmental
professionals is that the holding times for high molecular weight analytes,
such as PCBs, PAHs, organochlorine pesticides, and dioxins, could be
reasonably extended without adversely affecting the data quality. Organic
and inorganic parameters susceptible to degradation in storage, such as
VOCs, COD, BOD, TOC and alkalinity, should be analyzed as soon as
possible after sampling, especially at low-level concentrations (Popek,
2003).

4.1.4 Selection of Sample Containers

In selecting appropriate sample containers, the factors to be considered are costs,
ease of use, and cleanliness. More important to the data quality, the containers
should be compatible to the analytes in a particular matrix. For water samples,
containers are selected as follows:

Glass vs. plastics: Glass containers may leach certain amount of boron and
silica, and significant sorption of metal ions may take place on the
container wall. Glass containers are generally used for organic compounds,
and plastic containers are used for inorganic metals. For trace organics, the