There is always some uncertainty associated with an analytical response. The uncertainty can be divided into two main components:
- Uncertainty related to sampling
- Uncertainty related to the chemical analysis
The uncertainty contribution from the sampling is often significantly higher than the uncertainty contribution from the chemical analysis.
Sources of error in sampling:
- Systematic errors
- Varying composition of water (particles of different composition and shape; too poor mixing at the sampling point)
- Wrong sampling strategy (time proportional sampling instead of water volume proportional)
- Random errors
- Sampling is performed in different ways by different people
- The function of the sampling equipment varies (sometimes pulls) the sampler up large particles, other times not)
- The samples are treated differently from time to time