Self test 7 – Validation of liquid chromatography mass spectrometry (LC-MS) methods

1. What types of performance characteristics are described? Please choose correct characteristic.

Description	Characteristic
Mean value of 6 measurement results of the same sample was 5.2 mg/L, reference value was 5.0 mg/L.
Standard deviation of the mean of 6 titration results of the same sample was 0.02 mL.
Repeatability of the method obtained as the pooled standard deviation from 127 measurement results.
Measurement uncertainty was estimated as ±0.2 mg/L, k = 2.
Relative expanded uncertainty of the method is in the range of 0.9 – 1.1%, k = 2, depending on measurement conditions.
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. Which of the following is true?

Lab’s E_n number is 1.4. This is below 2, so the lab result is good and no action is needed from the lab.

Zeta-scores show agreement between the lab result and independent reference value.

E_n numbers show agreement between the lab result and consensus value.

Zeta-score does not have units.

Lab’s zeta-score is 3.2. This is above 3, so the lab result is unacceptable and corrective action is needed from the lab.

The units of the E_n number are the same as the used concentration units.

3. Which of the following is true?

Lab’s z-score -2.5. This is below 2, so the lab result is good and no action is needed from the lab.

Z-scores show agreement between the lab result and independent reference value.

Z-score does not have units.

Lab’s z-score is 3.5. This is above 3, so the lab result is unacceptable and corrective action is needed from the lab.

The units of the z-score are the same as the used concentration units.

Outlier elimination has to be carried out after calculating the consensus value and target standard deviation.

Outlier elimination has to be carried out before calculating the consensus value and target standard deviation.

Z-scores show agreement between the lab result and target standard deviation.

Outlier elimination has to be carried out after calculating the consensus value but before calculating the target standard deviation.

Z-scores show agreement between the lab result and consensus value.

4. In an interlaboratory comparison, Lab’s result is 12.6 mg/kg with combined standard uncertainty 1.1 mg/kg. The independent reference value is 13.8 mg/kg with combined standard uncertainty 0.5 mg/kg. Which of these – zeta-score, E_n number, z-score – can be calculated from these data? Please calculate them and present the answers with 2 decimals. If cannot calculate, please type N/A.

	Answer
zeta-score
E_n number
z-score

Is the lab result in agreement with the reference value?