WHAT IT IS
Mass accuracy in mass spectrometry (MS) refers to how closely the instrument's measured mass-to-charge ratio (m/z) of an ion matches the true or theoretical mass of that ion. It tells us how precisely the instrument can detect and report the exact mass of a molecule or element.
Mass accuracy is essential for identifying unknown compounds, confirming molecular formulas, and ensuring reliable quantitative and qualitative results. It is especially important in high-resolution mass spectrometry (HRMS) systems.
HOW IT WORKS
Every mass spectrometer detects ions by measuring how they behave under electric or magnetic fields. Each ion has a unique mass-to-charge ratio (m/z), and the instrument records this value.
The measured m/z is then compared to the known or expected mass of the ion. If the measurement is very close to the true value, the instrument has high mass accuracy.
IMPACT ON PERFORMANCE
Compound Identification: Accurate mass measurements help determine elemental composition, which is critical for identifying unknown substances or confirming chemical structures.
Library Matching: High mass accuracy improves confidence in spectral database searches, helping differentiate between compounds with similar nominal masses.
Isotope Ratio Precision: In isotope ratio and elemental MS, precise mass detection improves the accuracy of isotopic and elemental quantification.
Low False Positives: When analyzing complex mixtures, good mass accuracy reduces the chance of misidentifying compounds.
Data Quality: In regulated fields such as pharmaceuticals, food safety, and forensics, mass accuracy is a key requirement for method validation and regulatory compliance.
CHALLENGES AND LIMITATIONS
Instrument Drift: Over time, small changes in temperature, vacuum, or electronics can cause shifts in measured mass values. Regular calibration is needed.
Matrix Effects: In complex samples, background compounds can affect ion behavior, causing small shifts in measured m/z values.
Ion Overload: Very strong signals can distort accuracy, especially in instruments like TOF or Orbitrap.
Lower-Resolution Instruments: Instruments with low resolution may not separate ions that are very close in mass, making accurate measurement more difficult.
Calibration Quality: Poor or infrequent calibration can result in systematic errors across the entire m/z range.