What is the role of an internal standard in LC-MS/MS analysis?

What is the role of an internal standard in LC-MS/MS analysis?

• A. An internal standard reduces sample volume requirements by dilution.
• B. An internal standard corrects for matrix effects and instrument variation by normalizing analyte response to the standard, enabling accurate quantification.
• C. An internal standard is the target analyte used for calibration.
• D. An internal standard is used to preserve sample integrity in storage.

Answer: (B)

In LC-MS/MS quantification, an internal standard provides a stable reference that compensates for variability across the run. It is a compound chemically similar to the target analyte (often a stable isotope-labeled version) added in a constant amount to every sample, calibration standard, and blank. Because it behaves similarly during extraction, chromatography, and ionization, any losses or matrix effects affect both the analyte and the internal standard in roughly the same way. By taking the ratio of the analyte signal to the internal standard signal, you correct for those variations, yielding accurate and precise quantification even when the sample matrix suppresses or enhances ionization or when instrument conditions drift. The internal standard is not the actual analyte being measured, nor is its purpose to preserve samples or reduce volume; its role is to normalize responses for reliable calibration and measurement.