Estimation of measurement uncertainty in chemical analysis

Self-test 4.1

Here you can test your understanding of some important aspects of uncertainty estimation related to pipetting.

1. Is it a good idea to rinse the pipette before pipetting?

Yes

2. Is it mandatory to always use pure water for pipette calibration?

Yes

3. What are the three main uncertainty sources by pipetting?

Uncertainty due to temperature difference during calibration and during measurement

Latitude of the location pipetting (is it done near the pole or near the equator)

Uncertainty of the water density

Uncertainty of calibration (uncertainty of the position of the mark on the pipette)

Repeatability

4. What is standard uncertainty of repeatability if the individual measurement results are 4.55, 4.68, 4.57, 4.61, 4.78 and 4.49 mg/l? Please present answer with 2 significant digits.

5. What is the repeatability standard uncertainty of the mean value of six measurement results 7.74, 7.96, 7.77, 7.84, 8.13 and 7.63 ppm? Please present answer with one significant digits.

6. What would you use as volumetric flask calibration standard uncertainty estimate if the tolerance written on the flask is ± 0.08 ml? Please give the answer with 2 significant digits.

7. What would you use as the estimate of standard uncertainty due to chemical interference if it is known that the interference will not influence the result by more than ±0.5 mg/kg? Please give the answer with 2 significant digits.

8. What is the standard uncertainty of standard solution concentration if the concentration on the label reads as (0.1067 ± 0.0006) mg/l (k = 2)?