Validation of liquid chromatography mass spectrometry (LC-MS) methods

Self test 5.2A

1. What is bias?

2. Choose the correct answer from the drop-down menu for each case: short-term bias, not a bias or long-term bias.

  • All the results of a specific day are systematically influenced by the calibration graph of that day
  • Delicate analyte partially decomposes during sample preparation leading to lowered results
  • The titrant concentration determined on a particular day is slightly lower or higher than the true concentration
  • Because of the specifics of the used sample preparation procedure the sample is digested incompletely, leading to lowered values
  • During titrations we get every time slightly different result as previously

3. Does bias depend on the time frame?

4. Which effects are systematic within day and which are systematic in long term?

Effect Systematic within day Systematic in long term
Calibration graph of a specific day
Injection volume of autosampler is 5% higher than nominal
Delicate analyte partially decomposes at room temperature before samples are loaded into cooled autosampler
Repeatability of peak integration
Ionization suppression in the ESI source by a co-eluting compound
Baseline noise

5. Which are important issues in determining bias?

6. When we should use different bias types?

 

Way of expressing Formula When to use?
Absolute bias bias=Clab_mean-Cref
Relative bias bias=(Clab_mean-Cref)/Cref
Recovery R=Cuncorrected/Cref
Recovery R=(C1-C0)/ΔC

7. Two analysts determined meropenem (an antibiotic) in blood plasma. Both needed to determine the recovery of the procedure. Which analyst did it more correctly?

8. What do the parts of the figure marked with numbers mean?

Bias and related concepts
1
Individual measured value

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Uncertainty range of Ci (Ci – U … Ci + U)

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Reference value

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Mean measured value

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Repeatability/Reproducibility

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Bias

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2
Individual measured value

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Uncertainty range of Ci (Ci – U … Ci + U)

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Reference value

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Mean measured value

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Repeatability/Reproducibility

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Bias

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3
Individual measured value

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Uncertainty range of Ci (Ci – U … Ci + U)

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Reference value

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Mean measured value

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Repeatability/Reproducibility

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Bias

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4
Individual measured value

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Uncertainty range of Ci (Ci – U … Ci + U)

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Reference value

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Mean measured value

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Repeatability/Reproducibility

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Bias

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5
Individual measured value

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Uncertainty range of Ci (Ci – U … Ci + U)

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Reference value

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Mean measured value

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Repeatability/Reproducibility

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Bias

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6
Individual measured value

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Uncertainty range of Ci (Ci – U … Ci + U)

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Reference value

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Mean measured value

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Repeatability/Reproducibility

Unselect

Bias

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