Self-test 4.4 – Estimation of measurement uncertainty in chemical analysis

1. Which of the following is true? There are 5 correct answers.

Expanded uncertainty is roughly equal to the measurement error

Expanded uncertainty is roughly equal to the measurement bias

Expanded uncertainty is found by multiplying combined standard uncertainty with a coverage factor

Combined standard uncertainty is standard uncertainty that has been calculated taking into account all relevant uncertainty sources

Standard uncertainty is uncertainty expressed at roughly 68% confidence level

Standard uncertainty can be found, depending on situation, as standard deviation of parallel measurement results or standard deviation of the mean of parallel measurement results

Expanded uncertainty is found by adding the standard uncertainties of all input quantities

Expanded uncertainty expresses the range of values within which the true value lies with 100% probability

Standard uncertainty is uncertainty that is found using a standard approach

Combined standard uncertainty can be calculated from expanded uncertainty by applying square root

Combined standard uncertainty can be calculated from expanded uncertainty by dividing it with the coverage factor

Combined standard uncertainty is standard uncertainty expressed at roughly 95% confidence level

Expanded uncertainty is uncertainty that has been found by taking into account more uncertainty sources than in the case of standard uncertainty

2. The result of cadmium determination in waste water was 2.3 mg/l with combined standard uncertainty 0.21 mg/l. Please express the expanded uncertainty with 95% coverage probability (normal distribution can be assumed).

3. The maximum allowed limit of nitrate content in potatoes is 140 mg/kg. Which of the following results can we consider to be with 95% probability under this limit? In case of all results the normal distribution can be assumed.

120 mg/kg with relative combined standard uncertainty 10%.

128 mg/kg with combined standard uncertainty 8 mg/kg.

132 mg/kg with expanded uncertainty 7 mg/kg, k=2.

112 mg/kg with combined standard uncertainty 12 mg/kg.

125 mg/kg with relative expanded uncertainty 10%, k=2.