Environmental Engineering Reference
In-Depth Information
Microbial degradation
Chemical reactions
Chemical addition
(Acid, base, biocide)
Refrigeration
(Cool 2-6
Volatilization
°
C and dark)
Adsorption
Proper container
(Glass or plastic)
(Cap/septum)
(Amber bottle)
Absorption
Diffusion
Photoreaction
Figure 4.1 Methods of sample preservation to minimize potential changes of analytes during
sample transportation and storage
As shown in Figure 4.1, refrigeration (including freezing) is a universally
applicable method to slow down all loss processes. The only exception that
refrigeration does not help is when acidified water samples are preserved for metal
analysis. Cold storage will adversely reduce metal solubility and enhance
precipitation in the solution. The proper selection of containers (material type and
headspace) is critical to reduce losses through several physical processes, such as
volatilization, adsorption, absorption, and diffusion. Colored (amber) bottles help
preserve photosensitive chemicals such as PAHs. The addition of chemicals is
essential to some parameters for their losses due to chemical reaction and bacterial
degradation. Chemical addition or pH change can also be effective to reduce metal
adsorption to glass container walls. Table 4.1 lists examples of chemical loss
mechanisms and the preservation methods.
Table 4.1 Preservation methods of selected analytes and their physicochemical and
biological changes during sample storage
Analytes
Change during storage
Preservation
Metals (M)
Adsorption to glass wall Use plastic bottle
Precipitation (MO, M(OH) 2 ) Add HNO 3 to pH < 2
Phthalate ester
Diffusion from plastics
Use Teflon or glass bottle
Oil
Adsorption to plastics
Use glass bottle
VOCs
Volatilization
Avoid headspace
NH 3
Volatilization Add H 2 SO 4 to pH < 2
S 2
Volatilization Add zinc acetate and NaOH to pH > 9
CN
Volatilization
Add NaOH to pH > 12
Chemical reaction with Cl 2
Add ascorbic acid to remove free Cl 2
Organic
Chemical reaction with Cl 2
Add Na 2 S 2 O 3 to remove free Cl 2
(drinking water)
PAH
Photochemical degradation
Use amber glass container
Organic
Biodegradation
Low pH and temperature; add HgCl 2
to kill bacteria
Total phenolics
Bacterial degradation
Add H 2 SO 4 to stop bacterial degradation
Adapted from Keith (1988) and Popek (2003).
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