Self test 9.1 – Validation of liquid chromatography mass spectrometry (LC-MS) methods

1. Which definition of LoD is correct:

LoD is the true value below which the analysis method can never state the presence of the analyte

LoD is an estimated value that shows the limit where we can reliably say whether the analyte can be identified in the matrix with the particular analysis method

LoD is a characteristic that shows the capability of the used instrument (detector) to give information whether the analyte is present or not in any matrix

LoD is the value that shows if the analyte is present or not in the sample

2. Which definition of LoQ is correct:

The level at which it is possible to quantify the result with accuracy that is fit for purpose

The lowest concentration level of the calibration line

The lowest concentration under which quantification of the result is impossible

A level at least 10 times higher than LoD

3. Which of the following statement is true:

The pesticide imazalil was measured from an orange. The analyte was detected however the result is under the allowed MRL value. Therefore the analyte can be said to be present but in an allowed concentration.

A metabolite of a drug cannot be detected with a screening test from the saliva of a criminal – the drug has therefore not been used with 100% certainty

Melamine in milk powder is measured. The LoD value of the used analysis method is 1 mg/kg. The results show the content of 0.2 mg/kg and therefore this number should be reported as the result.

4. Which effects are not taken into account in instrumental LoD but are taken into account in method LoD:

Recovery of the analyte from the sample in sample preparation step

The electrical noise caused by the instrument

Sampling method

Matrix effects caused by the sample

Drift of the instrument signal in time

5. For what purposes can LoD value be used?

To interpret whether an analyte is present in the sample or not

To compare two analytical methods using LoD estimates found from literature. The LoD values have been estimated with different approaches.

To estimate whether the analyte can be said to be present in the sample at the level of LoD of the analysis method