1. What is Exact Mass?

Exact mass is the calculated mass of an ion or molecule using the mass of the most abundant isotope of each element. It differs from average molecular mass which considers natural isotopic abundances.

2. How Does the Calculator Work?

The calculator uses the exact mass formula:

Where:

• \( \text{Isotope Mass} \) — Mass of the specific isotope (in atomic mass units, amu)
• \( \text{Count} \) — Number of atoms of this isotope in the molecule

Explanation: The equation simply multiplies the mass of each isotope by how many atoms of that isotope are present in the molecule.

3. Importance of Exact Mass Calculation

Details: Exact mass is crucial in mass spectrometry for identifying molecular formulas, distinguishing between compounds with similar average masses, and for high-resolution mass measurements.

4. Using the Calculator

Tips: Enter the isotope mass in atomic mass units (amu) and the count of atoms. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between exact mass and average mass?
A: Exact mass uses specific isotope masses, while average mass uses weighted averages of all naturally occurring isotopes.

Q2: How precise should isotope masses be?
A: For high-resolution mass spec, use masses precise to 5-6 decimal places (e.g., 1.007825 for ¹H).

Q3: Can I calculate exact mass for multiple isotopes?
A: This calculator handles one isotope at a time. For multiple isotopes, you would sum the contributions from each.

Q4: Why is exact mass important in mass spectrometry?
A: It allows distinguishing between molecules with similar nominal masses but different elemental compositions.

Q5: Where can I find accurate isotope masses?
A: The IUPAC publishes authoritative tables of isotope masses and abundances.