Estimation of measurement uncertainty in chemical analysis

Self-test 7

Here you can test your understanding of the performance characteristics of analytical procedures: precision, trueness, accuracy.

1. What types of performance characteristics are described?

  1. Mean value of 6 measurement results of the same sample was 5.2 mg/L, reference value was 5.0 mg/l.
  2. Standard deviation of the mean of 6 titration results of the same sample was 0.02 ml.
  3. Repeatability of the method obtained as the pooled standard deviation from 127 measurement results.
  4. Measurement uncertainty was estimated as ±0.2 mg/l, k = 2.
  5. Relative expanded uncertainty of the method is in the range of 0.9 – 1.1%, k = 2, depending on measurement conditions.
  6. Analyte loss occurs during sample pre-treatment, causing systematically lower results. Lowering of the results has been estimated to be on an average 5%.

2. Accuracy refers to difference between the measured value and true value.

3. Trueness is an estimate of the difference between the mean of a large number of measured values and the true value.

4. Accuracy characterises the precision of a measurement result.

5. Accuracy characterises the random error of measurement.

6. Precision refers to the agreement between a measurement result and the reference value.

7. Reference value and true value are synonyms.

8. Precision characterises the scatter of replicate measurement results.


 

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