Self test 10.2 – MOOC: Validation of liquid chromatography mass spectrometry (LC-MS) methods (analytical chemistry) course

The same amount of perfluoroalkyl acids - perfluorohexanoic acid (PFHxA) and perfluorooctanoic acid (PFOA) was spiked to the different water matrices: ground water, surface water and sea water.

Concentration of the PFHxA and PFOA was measured from these matrixes using LC-MS. Please indicate the correct answers based on the experimental data:

Compound/Sample matrix	Ground water (n=3) [ng/L]			Surface water (n=3) [ng/L]			Sea water (n=3) [ng/L]
PFHxA	11.4	11.2	12.6	18.9	17.7	17.5	15.7	15.6	15.4
PFOA	9.1	10.0	9.7	10.9	10.9	11.0	10.4	10.8	11.0

The change in the sample matrix influences PFHxA the most. PFOA remains more robust for the changes in the sample matrix.

Used LC-MS method is reliable measuring both analytes in three studies matrices.

Both analytes are robust for the changes in the sample matrix.

Indicate correct statements.

Different matrices can lead to different matrix effects and therefore influence also other validation parameters such as trueness, LoQ/LoD.

Sample preparation removes any interferences caused by different sample matrices.

Visually the same matrix contributes to the matrix effects the same way: an apple is always an apple and human blood plasma is always human blood plasma.

Indicate the validation parameters that are influenced by the differences in visually the same matrix:

Limit of detection/Limit of quantification

Selectivity

Ionization suppression/enhancement

Stability

Linearity

Recovery (trueness)