5. Prevention Techniques

Question 1

1. Why preservation

Answer 1

Chemical compounds become unstable with changes and exposure to time air light and increase in temp
chemical kinetics can increase

Question 2

Factors that affect unpreserved samples

Answer 2

Volatilization 
Adsorption
Diffusion 
precopotation 
chemical changes 
biodegration

Question 3

Purpose of preservation

Answer 3

to minimize the effects of these processes

Question 4

Volatilization

Answer 4

the rate dependent on vapor pressure of analyte, sample temp and surface area

Question 5

Volatilization - techniques

Answer 5

1. minimize headspace and sample agitation
2. keep sample cool
3. avoid agitation and do not vacuum filtration

Question 6

Adsorption - Techniques

Answer 6

1. Choose correct sample bottles and add acids if necessary
2. Chemical changes affect samples, (absorption of O2)
3. Do field tests and preserve quickly

Question 7

Adsorption - Metal and Organic analysis

Answer 7

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

Question 8

Diffusion - techniques

Answer 8

• 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

Question 9

Precipitation - techniques

Answer 9

Add acid as a preservative

Acid preservative must be added immediately after sampling or else extreme loses of analyte will occur

Question 10

Biodegradation - Technique

Answer 10

Store at reduced temp and extreme pH

Question 11

Holding time

Answer 11

the length of time a sample can be store after collection and preservation without significantly altering the analytical results

Question 12

Preserving waters

Answer 12

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

Question 13

water microbiological Samples

Answer 13

• 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

Question 14

water - chemical/ physical analysis

Answer 14

• 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

Question 15

Soil samples - Preservation

Answer 15

Use proper bottles and seal
minimize headspace
Keep at 4C