- Why preservation
Chemical compounds become unstable with changes and exposure to time air light and increase in temp
chemical kinetics can increase
Factors that affect unpreserved samples
Volatilization Adsorption Diffusion precopotation chemical changes biodegration
Purpose of preservation
to minimize the effects of these processes
Volatilization
the rate dependent on vapor pressure of analyte, sample temp and surface area
Volatilization - techniques
- minimize headspace and sample agitation
- keep sample cool
- avoid agitation and do not vacuum filtration
Adsorption - Techniques
- Choose correct sample bottles and add acids if necessary
- Chemical changes affect samples, (absorption of O2)
- Do field tests and preserve quickly
Adsorption - Metal and Organic analysis
Metal: use plastic bottles, Acidify to pH <2, Keep the metal ions in solution
Organics: use glass bottles, container should be rinsed with an organic solvent to remove oil at the lab
Diffusion - techniques
- use proper container type ad minimize headspace
- glass bottles lined with Teflon-lined caps and liners are the best choice because of their inertness
- keep headspace to a minimum as analytes can easily diffuse from the liquid to the gas phase
Precipitation - techniques
Add acid as a preservative
Acid preservative must be added immediately after sampling or else extreme loses of analyte will occur
Biodegradation - Technique
Store at reduced temp and extreme pH
Holding time
the length of time a sample can be store after collection and preservation without significantly altering the analytical results
Preserving waters
use the appropriate sample bottles and minimize the headspace when filling.
- add chemical preservative and check pH then keep sample at 4C with blue ice in a cooler
water microbiological Samples
- clean bottle + Sodium thiosulfate preservative (a chlorine neutralizer)
- examine the sample bottle for cracks, a missing seal or other signs that its sterility may be compromised
- Label the bottle w the water supp;y owner’s name, location of the water source and sampling location, date and time
- Keep at 4C, should not be frozen, Transport within 24h
water - chemical/ physical analysis
- a clean polyethylene bottle is sufficient
- Label with the water supply owner’s name location of the water source and sampling location, date & time
- Seal the container tightly to eliminate air oxidation and photochemical reactions
- Keep at 4C, should not be frozen, Transport within 24h
Soil samples - Preservation
Use proper bottles and seal
minimize headspace
Keep at 4C
