1. What is Exact Mass?

Exact mass is the calculated mass of an ion or molecule based on the most abundant isotopes of each element. It differs from molecular weight (average mass) by using exact isotopic masses rather than weighted averages.

2. How Does the Calculator Work?

The calculator uses the exact mass formula:

Where:

• \( EM \) — Exact mass (unified atomic mass units, u)
• \( A_i \) — Number of atoms of element i
• \( M_i \) — Atomic mass of element i (most abundant isotope)

Explanation: The calculator sums the products of each element's atomic count and its exact isotopic mass.

3. Importance of Exact Mass Calculation

Details: Exact mass is crucial in mass spectrometry for identifying molecular formulas, distinguishing between isobars, and confirming molecular structures.

4. Using the Calculator

Tips: Enter element counts in comma-separated format (e.g., "C6,H12,O6" for glucose). Element symbols are case-sensitive (first letter capitalized).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between exact mass and molecular weight?
A: Exact mass uses isotopic masses, while molecular weight uses average atomic masses weighted by natural abundance.

Q2: Why is exact mass important in mass spectrometry?
A: Modern high-resolution mass spectrometers can measure mass with such precision that exact mass can determine unique molecular formulas.

Q3: How precise should my exact mass calculation be?
A: Typically 4-6 decimal places are sufficient for most applications in mass spectrometry.

Q4: What elements are supported by this calculator?
A: Common organic elements (H, C, N, O, P, S, F, Cl, Br, I) are included. Others can be added as needed.

Q5: How does this differ from monoisotopic mass?
A: Monoisotopic mass is the exact mass of a molecule using the most abundant isotope of each element, which is what this calculator provides.