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 nominal mass (integer mass) by using precise isotopic masses rather than whole numbers.

2. How Does the Calculator Work?

The calculator uses the exact mass formula:

Where:

• \( EM \) — Exact mass in 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 atom count multiplied by its isotopic mass.

3. Importance of Exact Mass

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 the number of atoms for each element in your molecule. The calculator uses the most accurate isotopic masses available (12C, 1H, 14N, 16O, 32S).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between exact mass and molecular weight?
A: Exact mass uses isotopic masses of the most abundant isotopes, while molecular weight uses average atomic masses that account for all isotopes.

Q2: How accurate is this calculator?
A: It uses the most accurate published isotopic masses (typically accurate to 6 decimal places).

Q3: Why don't you include other elements?
A: This calculator focuses on the most common organic elements. Additional elements can be added as needed.

Q4: How does exact mass help in mass spectrometry?
A: High-resolution mass spectrometers can measure mass-to-charge ratios precisely enough to distinguish between different molecular formulas with similar nominal masses.

Q5: What are typical applications of exact mass calculations?
A: Drug discovery, metabolomics, proteomics, environmental analysis, and forensic chemistry all rely on exact mass measurements.