As physico-chemical and biological reactions occur in the soil and the water, sampling periods of short duration are recommended. Some chemical variables should be measured in-situ in a sub-sample (temperature, pH, redox potential, and electrical conductivity) whereas the main water sample is preserved to prevent reduction or loss of target analytes, and transported to the laboratory without delay and kept cool until further treatment. Preservation stabilizes analyte concentrations for a limited period of time. Some samples have a very short holding time (from few hours to some days).
Each analytical method available will have its own requirements for specimen preparation. The most appropriate sampling method specifications for each parameter can be found in many textbooks (e. g. SMEWW, 1998). They should consider, for each chemical parameter, the bottle type (glass/plastic, dark), preservative (acidification, cold), typical sample volume, the need of filtration, and maximum storage time.
