Analytical Measurement Techniques and Instrumentation
Core concepts
Candidates should understand spectrophotometry (Beer-Lambert law), turbidimetry, nephelometry, ion-selective electrodes, chromatography, mass spectrometry, and immunoassay formats. Know the difference between endpoint and kinetic methods, and between direct and indirect ISE measurements.
Instrumentation principles
Recall that absorbance is proportional to concentration and path length, and that stray light limits linearity at high absorbance. Understand cuvette quality, wavelength selection, and the role of blanks. For immunoassays, know competitive vs sandwich formats and the hook effect.
Traps in questions
- Confusing turbidimetry (measures light blocked) with nephelometry (measures light scattered).
- Forgetting that indirect ISE dilutes the sample, affecting results in abnormal protein states.
- Assuming the hook effect causes falsely low results in all assay formats.
- Overlooking the effect of stray light on linearity.
Worked rule of thumb
When absorbance exceeds the linear range, dilute and re-measure rather than extrapolate. When a sandwich immunoassay gives unexpectedly low results at very high analyte concentrations, suspect the hook effect and re-test at a dilution.
Study guidance
Link each technique to its measurement principle, its common interferences, and its typical clinical application.