Sampling theory Flashcards
Explain what the quality control procedure are: Control of equipment
To make sure the equipment is clean and works properly. See if the pH-meter measures correctly and the therometer as well.
Explain what the quality control procedure are: Duplicate
- To get an average value
- Two samples at the same location
- They should show the same results
- Should be done with the same equipment, same time, same location and same sampler
Explain what the quality control procedure are: Blank
To make sure there are no contaminants comping from the equipment itself. Usually done with milli-Q water aka deionized
Explain what the quality control procedure are: Comparison of sampler
Two persons taking the same sample at the same location at the same time with the same equipment
You suspect that you and your colleague, in some way, do not sample in the same way and introduce an error. How could you assess this error and show if it is real or not? How would you statistically evaluate this difference?
- See if both are sampling the same way. Example, they take the lid off on land, then fill the bottle with water and screw it back on, I take the lid off under the water, fill the bottle and put the lid back on under water
- Then go through the sampling routines
- Compare with a blank sample?
- Test with known concentrations? To look at the techniques…
Describe one sistuation where knowledge about extreme concentrations is neccessary?
- Could be important to know how high/low the concentrations actually can be and when they were
- How bad could it be?
- What substance are they testing?
Describe one sistuation where knowledge about average concentrations is neccessary?
If there is a pollution or not since the extreme concentrations can be high if it is a low waterflow and they can be low if it is a high waterflow.
How are single and composite samples generated?
Single: - Concentration in the current sample is analyzed - Shows spatial or time variation if many samples are taken Composite: - Mean content - Several primary samples that are mixed - No spatial or time variation visible - Representative, more mean value
What are the pros and cons for each of the methods (single and composite)?
Single:
- Pros: Shows spatial or time variation (if many samples are taken)
- Cons: Requires many samples to get a good view of the natural variation. Risk of extreme values
Composite:
- Pros: More reliable estimation of the mean. Cost efficient
- Cons: Cannot be used for volatile hydrocarbons. Increased risk of cross contamination. Trends or patterns not visible
Which sampling dimension is the best?
- The 0-dimension
- You get an average measurement over the whole composition. The whole pile is split down to smaller piles. Then every small pile has an equal chance to get sampled.
Why is 0-dimension a privileged situation? Use the principle of sampling theory to explain.
It is not always possible to sample in 0-dimensional, since the thing you are sampling on may not be a heap, it’s more of a mountain. Then you go from doing a 3-dimensional and from there break it down to 0-dimensional
Explain the advantages and drawbacks of using: random or stratified/partially stratified
Random:
- All locations are randomly spread out over the whole area.
- Drawbacks: risk to miss the source, all locations could be very close to each other
- Advantages: easy method, no human effect
Stratified sampling:
- The locations that are not possible to sample is taken away.
Explain the advantages and drawbacks of using: systematic sampling
- Squares, in the middle of the square. Same distance between all locations.
- Drawbacks: the patterns can easily under- or overestimate, time demanding
- Advantages: easy to follow, even distribution of sampling locations, good view over the whole area
Explain the advantages and drawbacks of using: systematic random sampling
- Random in the square.
- Drawbacks: locations could end up where it’s hard to sample or very close to each other
- Advantages: good view over the area
How much material is “really” analysed when addressing VOC?
5 gram
