Free Mass Accuracy Calculator
Calculate mass accuracy in parts per million (ppm) for mass spectrometry measurements.
Mass Error (ppm)
1.67 ppm
Mass Error (ppm) vs Measured m/z
Mass Accuracy in Mass Spectrometry
Mass accuracy is the difference between the measured and theoretical mass of an ion, expressed in parts per million (ppm). It determines how confidently you can assign a molecular formula.
Formula
Error (ppm) = (m_measured - m_theoretical) / m_theoretical × 10⁶
Modern high-resolution instruments achieve < 2 ppm (Orbitrap) or < 1 ppm (FT-ICR). Time-of-flight (TOF) instruments typically achieve 2-5 ppm.
Example Calculation
Glucose [M+H]+ measured at 180.0637, theoretical 180.0634.
- 01Error = (180.0637 - 180.0634) / 180.0634 × 10⁶
- 02Error = 0.0003 / 180.0634 × 10⁶ = 1.67 ppm
- 03Error in mDa = 0.3 mDa
Frequently Asked Questions
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